Using The 4S6553 Engine Evaluation Test Group{0781} Caterpillar


Using The 4S6553 Engine Evaluation Test Group{0781}

Usage:

All Caterpillar Turbocharged Diesel Engines And Turbocharged Or Naturally Aspirated Natural Gas Engines

The 4S6553 Engine Evaluation Test Group can be used to analyze the engine performance of the above engines. It can also be used to make operating adjustments to natural gas engines. The performance evaluation assumes that if the engine is in good condition and all adjustments are correct, then the manifold pressure is a function of the power being developed.

Engine Evaluation Test Group Components


1. 1P7443 Tachometer

2. Tachometer Forward-Reverse Switch

3. Tachometer Input

4. Continuity Indicator

5. Continuity Input

6. 4S6997 Manifold Pressure Gauge

7. Manifold Pressure Inputs

8. 5P6579 Differential Pressure Gauge

9. 5P6579 Differential Pressure Gauge

10. Differential Pressure Inputs

11. 1P7447 Pressure Gauge

12. Psi Input

13. 1P7444 Tachometer Generator

14. 1P7445 Electric Tachometer Cable

15. 1P7448 Mechanical Tachometer Cable

16. 5P2948 Fittings

17. 2A4716 Dust Caps

18. 4K9822 Nuts

19. 4K9821 Sleeves

20. 1P7446 Rack Terminal Cable

21. 4S8381 Tube (50 ft - order by the foot)

22. 5P9693 Cable Ties

23. 3K6675 Fittings

24. Storage Container for Fittings

Tachometer

The 1P7443 Tachometer is a direct reading tachometer with a range of 0 - 4500 RPM. The tachometer scale indicates 1000 RPM for each revolution of its pointer, and multiples of 1000 RPM are shown in the window on the left of the dial face. The instrument is calibrated with a tachometer generator which produces a voltage relative to one-half engine speed. Tachometer accuracy in the following ranges is: ± 25 RPM @ 0 - 1200 RPM, ± 15 RPM @ 1200 - 2300 RPM, ± 25 RPM @ 2300 - 3000 RPM, and ± 40 RPM @ 3000 - 3500 RPM.

The 7M6001 Tachometer Drive Adapter Group used on some 4.0" and 4.5" bore engines and some special tachometer drives runs at engine speed. On engines with this adapter group, the 5S6106 Adapter must be connected to the tachometer drive, and the tachometer generator connected to the adapter. This will reduce the generator speed to one-half engine speed and will prevent overspeeding of the tachometer.

The 5S6106 Adapter and other tachometer adapters are shown in the TOOL GUIDE. A 5L2277 Tee Adapter can be used to check the accuracy of the machine tachometer against the 1P7443 Tachometer by allowing both tachometers to run at the same time. The outputs at the ends of the tee turn in opposite directions; therefore, a tachometer forward-reverse switch is used to accept either clockwise or counterclockwise rotation.

Pressure Gauge

The 1P7447 Gauge is used to check the fuel delivery pressure on natural gas and diesel engines. This gauge has a range of 0 - 100 psi and an accuracy of ± 2 psi. If a different pressure range gauge is needed for special applications, use one of the gauges in the 5P6225 Hydraulic Test Box.

Continuity Indicator

The continuity indicator is used to indicate governor balance point on engines equipped with a brass screw terminal on the governor housing. One lead of the rack terminal cable is clipped to this terminal, and the other lead is clipped to ground. When the rack stop collar just touches the torque spring, the light just barely comes on (a dim, flickering light). Power is received for the light from the tachometer generator so the indicator will not work unless the engine is running. CAUTION: Use the continuity indicator only while using the 4S6553 Test Group because a battery powered indicator might interfere with the tachometer generator voltage and cause incorrect tachometer readings.

Manifold Pressure Gauge

The 4S6997 Gauge is a duplex manifold pressure gauge with a range of 15 to 100 inches of mercury (Hg) absolute and an accuracy of ± 1.8 inches of mercury. The gauge reads absolute pressure. This is barometric pressure plus the boost from the turbocharger. The use of an absolute pressure gauge simplifies the test procedure on some engines and provides a barometric pressure reading without requiring an additional gauge. The duplex gauge permits reading two pressures, such as both banks of a V-type engine, or for comparing manifold pressures between two engines carrying a common load. If only one pressure tap is required, the other needle of the gauge provides a continuous barometric pressure. The connections to the gauge are made at the manifold pressure inputs shown on page 2. The fittings are marked to indicate which gauge needle will be connected.

Differential Pressure Gauges

The differential pressure gauges read the difference between two pressures. They have a range of 0 to 50 inches of water and are accurate within ± 1.0 inches of water. The gauges have two inlet ports - one for the higher pressure and the other for the lower of the two pressures. The gauge will then indicate the difference between the two pressures. If one port is left open to the atmosphere, the gauge can be used to measure the difference between atmospheric pressure and the test pressure. If the high pressure port is connected and the low pressure port left open, the gauge can be used to read a positive pressure, such as the exhaust back pressure due to a muffler. By connecting the low pressure port and leaving the high pressure port open to the atmosphere, a vacuum can be read, such as the inlet restriction through an air cleaner. If both ports are connected to positive pressures, such as the gas delivery pressure and inlet manifold pressure of a turbocharged natural gas engine, the gauge will read the difference between the two pressures.

Two differential pressure gauges also permit simultaneous reading of both inlet restriction and exhaust back pressure when road testing vehicle engines. The gauges and inputs are identified by the letters DP1 and DP2 stamped beside each gauge and the appropriate inputs as shown on page 2. Each input is also identified by the letter "H" or "L" stamped near the input to identify the high and low pressure connections.

Each gauge has a zero adjusting screw. When necessary, adjust the screw so the gauge reads zero with no connections to the gauge fittings.

Maintenance Of The 4S6553 Engine Evaluation Test Group

(A) Cleaning The 4S6997 Manifold Pressure Gauge

If duplex pointers (1) do not lie directly on top of each other when the gauge is open to atmospheric pressure at both ports, the gauge may need to be cleaned. Remove the gauge from the test box. Remove elbows (2) and slotted needles (3). Clean the slots in needles (3) with a piece of fine wire. Install the two needles and elbows.

If the pointers still do not lie directly on top of each other, return the gauge to the manufacturer for repair. See REPAIR AND CALIBRATION OF THE TEST GROUP.

(B) Troubleshooting The Tachometer System

The tachometer system on the 4S6553 Engine Evaluation Test Group consists of the 1P7445 Electric Tachometer Cable, the 1P7443 Tachometer and the 1P7444 Tachometer Generator. These parts can be ordered separately. Use the following procedure to determine which component needs replacement if the system does not operate correctly.

Use a continuity test light to check the 1P7445 Electric Tachometer Cable. If there is no continuity, replace the cable.

Use a volt-ohm meter to check the resistance between test points A, B and C. The following values should be obtained with the tachometer generator disconnected.

The test values may be in the range of column 1, 2 or 3 depending on where the tachometer was manufactured. However, the values for all three test points must be within the same range. If they are not, replace the tachometer.

Two tests can be performed to determine if the 1P7444 Tachometer Generator is operating correctly. Use a volt-ohm meter to check the resistance between test points A, B and C. The following values should be obtained with the tachometer disconnected.

If the test values are not within the above range, replace the tachometer generator. If the test values are marginal, perform the following test to determine the maximum and minimum output voltage from the generator. Use an AC voltmeter to perform the following test.

Install the tachometer generator on an engine or on the fuel injection test bench. Connect the tachometer generator to the tachometer with the cable. Disassemble the connector on the tachometer end of the cable as shown. Increase the engine speed to 2500 RPM (1250 RPM on the test bench). The maximum voltage between any two test points must be 24 VAC. Decrease engine speed to 600 RPM (300 RPM on the test bench). The minimum voltage between any two test points must be 3.5 VAC. If the tachometer generator fails either test, it must be replaced.

(C) Repair And Calibration Of The 4S6553 Engine Evaluation Test Group

If it becomes necessary to repair or calibrate the test group, return the unit to the manufacturer. Do not send the unit to Caterpillar Tractor Co. for warranty or repair as this will result in unnecessary delay. Aircraft Instruments and Development, Inc. warrants each item supplied Caterpillar Tractor Co. to be free from defects in material and workmanship as prescribed by the applicable specification and when used with reasonable care. The warranty shall be effective for twenty-four calendar months from the date of manufacture stamped on the part, and extends to the repair or replacement of the defective part only. Articles returned for warranty consideration, repair or calibration should be packaged in a manner to prevent damage in transit, and in accordance with the best commercial practice for fragile, high value items. Instruments should not be shipped parcel post. Return the unit to:

Aircraft Instruments and Development, Inc.
317 E. Lewis
Wichita, Kansas 67202
Telephone (316) 265-4271

The mechanical drive tachometer in earlier 4S6553 Engine Evaluation Test Groups should be sent to:

Masstech
80 Cambridge Street
Worcester, Mass. 01603
Telephone (617) 791-8118

General Information

Full Load Speed

Full load speed is the engine speed at which rated horsepower is developed and the fuel rack is positioned to allow the maximum recommended amount of fuel to the engine per unit of time. Usually, governor balance point and full load speed take place at the same engine speed. In some cases however, full load speed and the balance point are not at the same RPM; to facilitate transmission shifts, in some applications, the engine is designed to provide increased horsepower when the torque spring is deflected. This increased horsepower is called the "BHP Spread". When the full load speed and governor balance point occur at the same engine RPM, the fuel flow rate, turbocharger speed, air inlet manifold pressure and horsepower will also be at a maximum at this RPM.

Governor Balance Point

The governor balance point is the engine RPM at which the rack stop collar or adjusting screw just touches the torque spring or stop. A "balance" exists between the governor spring force and the governor weight force at this engine RPM. The governor balance point is a function of engine speed, the rack setting and the high idle setting.

Inlet Air Restriction

This is a measurement of the vacuum in the engine air inlet piping due to the air cleaner and inlet piping.

Inlet Manifold Pressure

The inlet manifold pressure (or "boost") is the pressure of the air being delivered to the engine in the inlet manifold. Inlet manifold pressure parallels engine horsepower and is a valuable key in determining engine performance. Inlet manifold pressures for Caterpillar engines are expressed in inches of mercury (Hg), and the specifications are given in the Rack Setting Information Book.

Lugging

An application of a load to an engine so as to cause the engine speed to fall below the rated speed. If the engine is lugged below the maximum torque point, it will stall unless some of the load is removed.

Pressure Ratio Control

This is a device used on some engines to limit the "boost" pressure delivered by the turbocharger. The pressure ratio control bypasses part of the exhaust gas around the turbine when the inlet manifold pressure reaches a specific pressure relative to the inlet air pressure.

Diesel Fuels

Many times the reason for low power output from diesel engines is the use of a light grade of diesel fuel. The power output from diesel fuel is, in part, the result of its BTU content per gallon (BTU = British Thermal Unit). The BTU content per gallon is in direct relation to the density (specific gravity) of the fuel. By measuring the specific gravity of the fuel in API (American Petroleum Institute) units, the effect of fuel density on engine performance can be found. The higher the API gravity, the lower the fuel density and thus the lower the heat or burning value of the fuel per gallon. If fuel of more than 35° API gravity is used in a Caterpillar engine, then less than rated horsepower will be the result. On the other hand, if fuel of less than 35° API gravity is used, then actual horsepower will be more than rated horsepower.

The horsepower ratings of diesel engines given in the Caterpillar Rack Setting Information Book were measured while using standard No. 2 diesel fuel of 35° API gravity at a fuel temperature of 60°F. (The API gravity is variable according to the temperature of the fuel.) Because of the availability of some fuels - and the wide range of fuels that a Caterpillar engine can use - the API gravity is usually not exactly 35° API. If the fuel being used is not 35° API, then the actual horsepower can be more or less than the rated horsepower. Fuels outside the general range of 32° API to 45° API are not normally used in Caterpillar engines. There are also some fuels in the general range of 32° API to 45° API that are not recommended. See the graph below for the general effect of fuel API gravity on engine performance.

Note 1: Beyond 44° API, results are not easily predictable.

Note 2: Few fuels outside the range of 32 - 44° API also have suitable cetane ratings and sulphur content, etc.

Note 3: Most common applications of Caterpillar Engines are within the center area.

In addition to API gravity in the desired range, fuel should have a minimum cetane number of 35 to be used in precombustion chamber engines and should have a minimum number of 40 to be used in direct injection engines. The Cetane Number Scale (by the American Society for Testing and Materials) is in reference to the ignition quality of the fuel. During injection of fuel into the combustion chamber, ignition is not immediate. If the cetane number is too low, the delay in ignition is too long. The engine may be hard to start; when the fuel does not burn, the engine may run rough or "knock."

For more information on the correct fuels to use in Caterpillar diesel engines, see Special Instruction Form FM055165-02, the March 7, 1974 issue of Service Magazine on "Fuels for Caterpillar Diesel Engines", and Service Training Meeting Guide No. 181 (Pages 21-24).

NOTE: Most Caterpillar vehicles at shipment from the factory have fuel in the 42° API to 47° API gravity range (for storage, corrosion resistance, and easy starting during shipment), although they should be operated on standard No. 2 diesel fuel (35° API gravity). Remember this when checking the performance of a new engine. See the April 10, 1972, Service Magazine for more information.

Pretest Conditions

If the 4S6553 Engine Evaluation Test Group is to be used to determine engine horsepower (instead of just measuring boost), the engine must be in good condition and all adjustments must be correct. If these conditions exist, then the inlet manifold pressure is a function of the power being developed. This is true for turbocharged diesel engines and both turbocharged and naturally aspirated natural gas engines.

For turbocharged diesel engines perform the following checks:

1. Check the fuel delivery rate with the engine at full load. If this is not possible, check the static rack setting. Make sure the governor control linkage is not binding, and that the high idle setting can be obtained.

2. Use the 1P540 Flow Checking Tool Group to check the fuel injection timing. Make a correction to the lifter settings if necessary. Correct fuel injection timing is very important; incorrect timing can result in correct inlet manifold pressure but less than rated horsepower. If the engine is equipped with a timing advance, check the timing with a 1P3500 Fuel Injection Timing Light.

3. Check the combustion chamber condition using the cylinder condition analyzing tools to check for leaking piston rings or valves. See Special Instruction Form GMG00694.

For natural gas engines, check all operating adjustments, the spark plugs, magneto timing, load screw setting, etc. and make corrections as necessary.

Connecting The Engine Evaluation Test Group To The Engine


All gauge connections are made with lengths of plastic tubing (1) cut to the desired length. The connections are made to pressure inputs (2), (3) and (4) on the test group. The electric tachometer cable (5) is plugged into tachometer input (6) and connected to tachometer generator (7) which is installed on the engine Service Meter. Mechanical tachometer cable (8) can be used for remote mounting of the tachometer generator in limited space installations. The rack terminal cable (9) is plugged into continuity input (10).

(A) Turbocharged Diesel Engines Without A Pressure Ratio Control

1. Connect the manifold pressure gauge to the pressure tap on the engine. See the Service Manual for the location of the pressure tap. Leave one tap on the gauge open to the atmosphere.

2. Use the electric tachometer cable to connect the tachometer to the tachometer generator mounted on the engine Service Meter.

3. Connect the low pressure tap on differential pressure gauge No. 1 to the air inlet pipe or top of the air cleaner service indicator on the engine. Leave the other tap open to the atmosphere.

4. Connect the high pressure tap on differential pressure gauge No. 2 to the turbocharger exhaust elbow on engines with mufflers or lengthy exhaust piping. Use a 6" pipe nipple between the exhaust elbow and the plastic tubing to prevent damage to the tubing. Leave the other tap open to atmosphere.

5. Connect the 0-100 psi gauge to the fuel pressure gauge tap on the fuel filter housing.

6. Connect one lead of the continuity indicator cable to the brass screw terminal on the governor housing and the other lead to ground.

(B) Turbocharged Diesel Engines With A Pressure Ratio Control

1. Connect needle No. 1 of the manifold pressure gauge to read manifold pressure after the turbocharger. See the Service Manual for the location of the manifold pressure tap on the engine.

2. Install a 1F9369 Tee (1/8" street tee) in the tapped hole in the turbocharger air inlet pipe or on top of the air cleaner service indicator. Connect needle No. 2 of the manifold pressure gauge to the tee to measure barometric pressure of air entering the turbocharger. Connect the low pressure tap of differential pressure gauge No. 1 to the other side of the tee to read air cleaner inlet restriction. Leave the other tap on differential pressure gauge No. 1 open to the atmosphere.

3. Connect the high pressure tap of differential pressure gauge No. 2 to the turbocharger exhaust elbow on engines with mufflers or lengthy exhaust piping to measure exhaust back pressure. Use a 6" pipe nipple between the exhaust elbow and the nylon tubing to prevent damage to the tubing. Leave the other tap of the pressure gauge open to the atmosphere.

4. Use the electric tachometer cable to connect the tachometer to the tachometer generator mounted on the engine Service Meter.

5. Connect the 0-100 psi gauge to the fuel pressure gauge tap on the fuel filter housing.

6. Connect one lead of the continuity indicator cable to the brass screw terminal on the governor housing and the other lead to ground.

(C) Natural Gas Engines

1. Connect the manifold pressure gauge to the pressure tap located under the carburetor on G342, G353, G375, G379, G398 and G399 engines. On G333 and 3306 gas engines, the tap location is on the left side of the engine similar to the tap location on D333 and 3306 diesel engines. On G343 engines, the tap location is on the bottom of the aftercooler housing. When checking a V-type engine, the pressure tap in each manifold should be connected to the test group, one to each tap of the manifold pressure gauge.

2. Use the electric tachometer cable to connect the tachometer to the tachometer generator mounted on the engine Service Meter.

3. Connect the low pressure tap of differential pressure gauge No. 1 to the turbocharger air inlet pipe or the top of the air cleaner service indicator to obtain the air cleaner inlet restriction. Leave the other tap open to the atmosphere.

4. Connect the high pressure tap of differential pressure gauge No. 2 to the exhaust outlet on engines with mufflers or lengthy exhaust piping to measure the exhaust back pressure. Use a 6" pipe nipple between the exhaust outlet and the nylon tubing to prevent damage to the tubing. Leave the other tap open to the atmosphere.

5. Connect the 0-100 psi gauge to the fuel inlet on the regulator to measure fuel delivery pressure under load.

6. Install 2F7112 Thermometers to check the temperature of the air-fuel mixture to the engine. On turbocharged engines, install the thermometer in the air piping between the aftercooler and the carburetor (use a thermometer in the pipe to each bank on V-type engines). On naturally aspirated engines, install the thermometer in the air piping or near the air cleaner inlet (the air-fuel mixture in the manifolds of these engines is close to ambient air temperature as there is no compression of the air to add heat).

(D) Additional Parts Needed

Refer to the TOOL GUIDE for additional parts not included with the instrument group that may be needed in some applications. In addition to the parts shown in the TOOL GUIDE, it may be necessary to make the special fitting shown using a 3K6675 Fitting, 9B4446 Washer, and 2L4845 Nut to measure the exhaust back pressure on engines with wet manifolds.

Test Procedure - Turbocharged Diesel Engines Without A Pressure Ratio Control

1. Provide a means of loading the engine. On medium duty direct injection engines, run the engine at full load for a minimum of 10 minutes before making performance checks. Run all other engines at full load for 45 minutes before making performance checks.

NOTE: Refer to Special Instruction Form SEHS7050, "USING THE 5P2160 ENGINE HORSEPOWER METER ARRANGEMENT" for information on the loading of diesel engines. For information on the loading of marine engines, see Special Instruction Form SEHS6947, "REFERENCE MATERIAL AND CORRECTION FACTORS FOR USE WITH THE 5P2160 ENGINE HORSEPOWER METER ARRANGEMENT".

2. With the engine at operating temperature, put the governor control in the high idle position and load the engine until engine speed falls to approximately 80% of the full load speed.

3. Hold the engine speed at this value for 30 seconds. Slowly reduce the load while observing the increase in manifold pressure and engine speed.

4. The inlet manifold pressure will increase (as the load is decreased), reach a peak value and fall sharply. Watch the pressure peak and note the maximum manifold pressure and the speed at which it occurs. This is the full load speed of the engine.

5. If the maximum manifold pressure does not occur at the expected speed, adjust the high idle setting as necessary to obtain the full load speed. Raising the high idle will raise the full load speed; lowering the high idle will lower full load speed.

NOTE: The high idle speeds shown in the rack setting charts are nominal values only. The high idle speed obtained by the above procedure will usually be within 30 RPM of the published figures. However, the high idle setting must not be changed once the full load speed has been set. The setting required to obtain the full load speed takes precedence over published or stamped name plate specifications for high idle speed.

6. After the full load speed has been set, repeat the test procedure and make a record of the following information at the full load speed.

7. If the maximum manifold pressure is within specification and occurs at the correct engine speed, then an engine in good condition, with all operating adjustments correct, will be developing full rated horsepower. See DETERMINING BRAKE HORSEPOWER on page 11.

8. If the maximum manifold pressure is lower than the expected tolerance, the following items should be checked:

a) The procedure to load the engine. The manifold pressure will not come up to the maximum value unless full load is applied to the engine. In some cases, such as marine or some industrial engines, it may not be possible to control the load sufficiently to establish the balance point. An analysis of the engine speed, manifold pressure and rack setting under load should provide sufficient information to permit determination of the load applied to the engine and the engine's ability to handle the load.
b) At extremely high altitudes, the manifold pressure and horsepower may be reduced. Refer to the rating tag on the engine for altitude operation.
c) An air leak between the turbocharger discharge and engine (loose or missing plugs in manifold, leaking air compressor inlet piping, etc.).
d) Loose, cracked or leaking exhaust manifold or turbocharger.
e) Air inlet restriction (plugged air filter, restricted piping, etc.). Maximum inlet restriction must not exceed that shown on the data sheet.
f) Exhaust restriction (restrictive muffler, undersize piping, etc.). Maximum exhaust back pressure must not exceed that shown on the data sheet.
g) Low fuel pressure (plugged fuel filter, leaking bypass valve, etc.).
h) Low fuel rate (wire-brushed injection valves, worn pumps, etc.).
i) Binding rotating assembly in the turbocharger.
j) Remote governor control linkage to ensure that it will permit full governor travel.

9. If the maximum manifold pressure exceeds the expected tolerance, the cause must be determined and the condition corrected. The following items should be checked and corrected as necessary:

a) Deposits on the turbocharger nozzle.
b) Incorrect turbocharger or nozzle.
c) Incorrect governor and/or rack setting.
d) Incorrect fuel injection pumps or injection valves.
e) High aftercooler temperature.


NOTICE

EXCESSIVE MANIFOLD PRESSURE SHOULD NOT BE IGNORED AS IT IS AN INDICATION OF A CONDITION WHICH COULD RESULT IN PREMATURE ENGINE OR TURBOCHARGER FAILURE.


Determining Brake Horsepower

1. The horsepower rating and manifold pressure of turbocharged engines as listed in the Rack Setting Charts were obtained with an air inlet temperature of 85°F (29°C) and an API fuel gravity of 35 at 60°F (16°C). The horsepower must be corrected for fuel gravity on turbocharged and aftercooled engines. On turbocharged engines without aftercooling, the horsepower must be corrected for both air inlet temperature and fuel gravity.

2. Measure the API gravity and fuel temperature with the 1P7408 or 5P2712 Thermo-Hydrometer. See Special Instruction Form GMG00977 for more information. Use the table on page 12 to find the corresponding API gravity at 60°F from the observed reading on the thermo-hydrometer. Use the following table to find the horsepower correction factor for non-standard fuel.

API Gravity Corrected To 60°F

3. To correct for non-standard air inlet temperature, use a thermometer to measure the air inlet temperature at the air cleaner intake. Use the following table to find the horsepower correction factor.

Inlet Air Temperature Correction Factors

4. Calculate the expected horsepower by dividing the rated horsepower by the product of all of the correction factors.

EXAMPLE: Determine the expected horsepower of a turbocharged engine tested under the following conditions:

Published engine rating ... 300 BHP (± 3% at standard conditions)

Inlet air temperature ... 100°F(38°C)

Correction factor ... 1.008

Fuel gravity ... 40°API at 90°F(32°C)

Correction factor ... 1.0168

Examples Of Horsepower Determination

The graph on page 16 shows a comparison between the manifold pressure, rack position and horsepower for a 1673 Truck Engine. The manifold pressure and horsepower curves are very similar to those shown on the graphs on page 15, but the maximum manifold pressure is slightly higher than shown on page 15. As this pressure in both cases is within the expected tolerance, the variation is due to manufacturing tolerances and does not indicate any problem with either engine.

The horsepower, manifold pressure and rack position all increase rapidly as the engine is lugged back from high idle speed as shown by the graph on page 16. At full load, both the horsepower and manifold pressure will reach a definite peak. The rack position will increase slowly as the engine is lugged to speeds below full load due to the deflection of the torque spring. Both the manifold pressure and the horsepower developed will decrease as the engine is lugged below full load.

With an understanding of how the engine performance indicators follow the power output, it is possible to determine the load condition of the engine if the expected manifold pressure, engine speed and rack position at full load are known. For the 1673 Truck Engine, SN 70B1080 and up, the following information can be obtained from the Rack Setting Chart:

Static rack setting ... + .100 inches *

Full load horsepower ... 220 at 2200 RPM

Manifold pressure at full load ... 29.5 ± 3.0 inches of mercury


*This engine is equipped with a hydraulic governor. The rack position with the engine running will be approximately .015" greater than the static rack setting due to oil pressure in the governor. (See the Rack Setting Charts. Most current hydraulic governors have a .020" greater dynamic rack setting than static rack setting.)

In the following examples, a 1673 Truck Engine is being checked to determine its ability to carry a specified load. Although truck engines are usually easy to check, this particular engine is installed in an application where the load cannot be controlled.

EXAMPLE NO. 1 The engine has been run under load and the following data is obtained:

Dynamic rack position ... + .056 inches

Engine speed under load ... 2250 RPM

Manifold pressure under load ... 21.5 inches of mercury

Comparing these values with the established values, the engine speed is greater than the expected full load speed while the dynamic rack position and manifold pressure are lower than expected at full load.

The graph on page 16 shows that the load is not sufficient to require maximum horsepower from the engine. Under the conditions described, the engine will be developing approximately 180 horsepower. In this case, the engine is more than adequate for the load.

EXAMPLE NO. 2 Assume the following data is obtained.

Dynamic rack position ... + .134

Engine speed under load ... 1900 RPM

Manifold pressure under load ... 28.0 in. of mercury

Comparing these values with the established values, the engine speed is lower than the expected full load speed while the dynamic rack position is greater than expected at full load. The manifold pressure is slightly below the nominal expected pressure, but is within the expected limits. As the engine speed is below the full load speed, a drop in manifold pressure is to be expected.

From the graph on page 16, we can see that the engine is overloaded. Under the conditions described, the engine is being lugged to below full load speed and is developing approximately 210 horsepower at the lower speed. Since the speed is considerably below the expected full load speed, the performance would probably be unsatisfactory. In this case, the load on the engine should be reduced if possible.

The graph on page 17 shows the effect of low engine output and improper full load speed on the performance indicators. This data was also taken from a 1673 Truck Engine. The fuel injection valves installed in this engine had been cleaned with a wire brush, resulting in restricting the orifice and reducing the quantity of fuel which could flow through the valves. This caused the low horsepower value (190 BHP) shown. The full load speed also was not properly set as the maximum horsepower occurred at only 2162 RPM. If a full load speed check were performed on this engine, the following data would be obtained:

Comparing the test data with the values expected, it is apparent that the full load speed is low and that the power output, indicated by the manifold pressure, is considerably lower than normal. To obtain normal power from this engine, it would be necessary to properly set the full load speed and determine the reason for the lack of power as described in step 8 on page 10.

EXAMPLE NO. 3 Assume that the following data is obtained:

Rack position under load ... + .132 in.

Engine speed under load ... 1900 RPM

Manifold pressure under load ... 20.7 in. of mercury

Comparing this data with the normally expected values, it is apparent that an engine power problem does exist.

The rack position is slightly greater than the expected value at full load, and the engine speed is considerably less than that which would be expected. This definitely shows that the load applied is greater than the engine can carry at full load speed. The manifold pressure is well below the minimum value expected at full load speed. At the speed the engine is running, a slight drop in manifold pressure from the maximum reading would be expected, but not as large a drop as was obtained in this case. This shows that the engine is not producing full horsepower and should be checked to determine the cause of lack of power.

When checking an engine installation where the load cannot be controlled adequately to allow determination of the balance point and manifold pressure at the balance point, a comparison of the engine speed, manifold pressure, and rack setting obtained under load with normally expected values at full load will give a good indication of the engine's power output and ability to handle the load applied.


The above graphs show the comparison between inlet manifold pressure and brake horsepower at various engine speeds on 1673 Truck Engines. Note that both the manifold pressure and horsepower curves peak at the same speed. This peak occurs at the full load speed (and balance point in this application).

Test Procedure - Turbocharged Diesel Engines With Pressure Ratio Control

Because the pressure ratio control maintains a uniform manifold pressure over a wide range of engine speeds, the test procedure for engines with the pressure ratio control is different than the one for engines without a pressure ratio control.

The pressure ratio control reduces the maximum manifold pressure which the turbocharger can develop by controlling the amount of exhaust gas directed to the turbocharger. The graph below shows the actual manifold pressure with a pressure ratio control. The upper line on the graph shows the expected manifold pressure without a pressure ratio control. In this case if a pressure ratio control were not installed, the turbocharger would develop excessive speed and would be damaged.

With the pressure ratio control installed, the manifold pressure under full load will increase with an increase in speed until it reaches the value determined by the pressure ratio control assembly. This value is determined from the barometric pressure of the air entering the turbocharger and the pressure ratio setting of the control. As the engine speed increases, due to a reduction of the load, the manifold pressure will remain practically constant as the bypass valve opens to allow the excess exhaust gas to bypass the turbocharger until the engine speed has risen above the full load (maximum horsepower) speed. As the horsepower output is reduced, the temperature of the exhaust gas will decrease, tending to lower the speed of the turbocharger. The pressure ratio control assembly will compensate for this drop in temperature by partially closing and directing a larger percentage of the exhaust gas through the turbocharger. This will maintain a uniform pressure until the energy of the exhaust gas, even with the bypass valve completely closed and all exhaust gas entering the turbocharger, is insufficient to maintain the desired manifold pressure. Once this point is reached, the manifold pressure will fall off rapidly and follow the horsepower curve as shown.

Engine performance is analyzed by applying a load to the engine and observing the manifold pressure under load. If possible, the engine should be lugged well below full load speed to determine if the manifold pressure drops off when the engine is lugged.

Use the following procedure to evaluate the performance of an engine with a pressure ratio control.

1. Provide a means of loading the engine. Run the engine at part load until operating temperatures are reached.

NOTE: Most pressure ratio controlled engines are installed in machines equipped with a power shift transmission. Usually, the manifold pressure developed by the engine will be at the controlled value with the engine running at converter stall speed. When checking these engines, the engine can be loaded by placing the machine in top gear and applying the brakes while the governor control is in the high idle position. If the manifold pressure does not come up to the expected value, reduce the pressure on the brakes and allow the machine to creep. Watch the transmission oil temperature carefully during testing to avoid overheating.

2. With the governor control in the high idle position, load the engine to well below the full load speed and maintain it at a steady speed for at least 30 seconds or until the manifold pressure reading has stabilized. Gradually reduce the load on the engine, permitting engine speed to increase. If the manifold pressure indicated on the No. 1 needle of the gauge increases with an increase in engine speed, note the engine speed at which this pressure becomes constant.

3. When the engine speed has increased to the full load speed, hold the load constant and record the following data at full load speed.

4. Reduce the load, permitting the engine speed to increase, until the manifold pressure starts to fall off rapidly. Note the engine speed at which the manifold pressure starts to fall.

5. Use the chart on page 21 to determine if the manifold pressure obtained in step 3 is correct. Lay a straight-edge from the barometric pressure of the air entering the turbocharger (No. 2 needle) as shown in the left column, to the manifold pressure after the turbocharger (No. 1 needle) as shown in the right column. This line should pass through the mark on the center line corresponding to the pressure ratio control installed on the engine.

6. If the manifold pressure is within the tolerance expected and remains relatively constant over a fairly wide speed range, and all other readings obtained in step 3 are within limits, the engine should be performing satisfactorily.

7. If the manifold pressure remains fairly constant over a range of speeds but is not within limits, the following items should be checked:

a) Fuel pressure - on engines with fuel operated pressure ratio control, the minimum fuel pressure for proper operation is 20 psi.
b) Pressure ratio control.
c) Bypass valve on engines with fuel operated pressure ratio control.

8. If the manifold pressure does not remain constant over a range of engine speeds, the following items should be checked:

a) Procedure used to load the engine to ensure that the engine is fully loaded.
b) At extremely high altitudes, or with very high ambient temperatures, the speed range over which the manifold pressure will remain constant may be reduced from that obtained at normal altitudes and temperatures. If the fuel rack setting is reduced from high altitude operation, the speed range over which the manifold pressure remains constant may be reduced.
c) Air leak between the turbocharger discharge and engine (loose or missing plugs in manifold, leaking air compressor inlet piping, etc.).
d) Loose, cracked or leaking exhaust manifold or turbocharger.
e) Air inlet restriction (plugged air filter, restricted piping, etc.). Inlet restriction at full load should not exceed 30 inches of water.
f) Exhaust restriction (restrictive muffler, undersize piping, etc.). Exhaust restriction at full load should not exceed 27 inches of water on a turbocharged engine.
g) Low fuel pressure (plugged fuel filter, leaking bypass valve, etc.). Minimum fuel pressure for proper operation of a fuel operated pressure ratio control is 20 psi. Low fuel pressure may also affect performance of machines equipped with pneumatic pressure ratio controls.
h) Low fuel rate (wire brushed or defective injection valves, worn pumps, etc.).
i) Binding rotating assembly in the turbocharger.
j) Check governor control linkage to ensure that it will allow full governor travel.
k) API gravity of fuel used. The power rating of the engine and the expected manifold pressure are based on fuel of 35° API gravity. If lighter fuel is used, the power output from the engine, and the speed range over which the manifold pressure will remain constant, will be reduced. If the fuel used has a specific gravity other than 35° API, refer to step 2 on page 11 to get the corrected horsepower.
l) Proper operation of the pressure ratio control and the bypass valve.

Test Procedure - Natural Gas Engines

The 4S6553 Engine Evaluation Test Group can be used to make operating adjustments on natural gas engines and to determine the approximate power output of natural gas engines.

The manifold pressure gauge and differential pressure gauges can be used to make all the operating adjustments to the fuel system of natural gas engines. The tachometer can be used as a reference when making adjustments, but it is recommended that an accurate digital tachometer be used when taking critical speed readings.

The manifold pressure gauge can be used to make an approximate setting when balancing the manifold pressure in the two banks of a V-type engine. One needle can be connected into each bank to read the pressure in both banks. As the accuracy of this gauge is marginal for the final setting, it is recommended that the banks be balanced as closely as possible with the manifold pressure gauge, and then one of the differential pressure gauges be used for the final adjustment. The differential pressure gauges can be used for making all of the carburetor and regulator adjustments. Use of the 3B9389 Fittings at the test ports will speed testing by permitting switching of the gauges between ports without the need to shut off the engine. See the appropriate Operation Guide and Service Manual for test port connections, procedures and proper values.

The power developed by a natural gas engine, either naturally aspirated or turbocharged, can be determined from the manifold pressure (boost), temperature of the air-fuel mixture in the manifold, and the BTU content of the fuel. Always measure the manifold pressure under the carburetor butterfly for all horsepower calculations. This power determination is accurate only for an engine in good condition with all adjustments correct. Under laboratory conditions, accuracy as close as ± 3% is possible. Under field conditions, accuracy may be less.

Use the following procedure to check the power output of a natural gas engine.

1. Run the engine under load until it is at operating temperature. Make a record of the following information at full load speed.

Inlet manifold pressureEngine speedAir inlet temperatureAir inlet restrictionExhaust back pressureFuel delivery pressure

2. Refer to the charts on pages 24 through 37 of engine horsepower vs. manifold pressure (under the carburetor butterfly) for the engine being tested to determine the power developed by the engine under standard temperature conditions using 1000 BTU per cu. ft. natural gas for fuel.

NOTE: These charts may be extended slightly if necessary. If a curve is not shown for the engine speed desired, the data can be approximated from the data shown. For example, 900 RPM will be midway between the 800 and 1000 RPM curves.

3. The horsepower value obtained in step 2 must be corrected for temperature of the air-fuel mixture in the manifold (if the temperature is other than that listed below) and for the heating value of the fuel used if natural gas is not the fuel. Corrections may be calculated as follows.

Temperature Corrections

The power outputs obtained from the charts are based on the following air temperatures in the manifold.

Naturally aspirated - 90°FTurbocharged and aftercooled (high compression ratio) - 110°FTurbocharged and aftercooled (low compression ratio) - 150°F

Correction for air temperature may be made by multiplying the horsepower values obtained in step 2 by the following factors:

NOTE: When testing a V-type engine, the temperature in both manifolds should be averaged, and the average temperature used.

Fuel Corrections

The horsepower values are based on natural gas having a high heating value of approximately 1000 BTU/cu.ft. If propane or sewer gas is used as fuel, the power ratings should be corrected as follows:

a) If propane with a high heating value of approximately 2500 BTU/cu.ft. is used, increase the power output by 9%.

b) If sewer gas with a high heating value of 600 BTU/cu.ft. is used, reduce the power output by 7%.

4. As an example of the procedure to be used, assume that the test was run on a naturally aspirated G398 Engine with a high compression ratio. The following data was obtained:

Model - G398, naturally aspirated, 10:1 compression ratioManifold pressure - left 25.0 right 25.0Engine speed under load - 1000 RPMAir temperature in manifold - left 116°F right 86°F

If the inlet manifold restriction, exhaust restriction and fuel delivery pressure under load are within limits, then the power output can be determined as follows:

a) Refer to the Manifold Pressure (under the carburetor butterfly) vs. Horsepower chart for the G398 Engine on page 35. Locate the 25.0 in. of mercury manifold pressure in the portion of the chart pertaining to the 10:1 compression ratio naturally aspirated engine.

b) Draw a straight horizontal line from the observed manifold pressure (25.0 in. of mercury) to intercept the curve for the observed (1000 RPM) engine speed. This is line 1 on the chart on page 35.

c) Draw a straight vertical line from the interception of the manifold pressure and the engine speed curve to find the horsepower expected. This is line 2 on the chart.

d) From line 2, it is shown that the expected horsepower under standard conditions of temperature and fuel heating value is 392 horsepower. For non-standard conditions, use the formula in step 3 on page 22 for naturally aspirated engines as follows:

If a fan is installed, reduce this value by the amount of power required to turn the fan.

The above value is for an engine using natural gas as fuel. If sewer gas with a high heat value of 600 BTU/cu.ft. is used, the corrected horsepower must be further reduced by 7% as follows:

385 × .07 = 26.95

385 - 27 = 358 Horsepower

G33A Naturally Aspirated

G333A Turbocharged - Aftercooled

G333C/3306 Gas Naturally Aspirated

G333C/3306 Gas Turbocharged - Aftercooled

G342

G343 Naturally Aspirated

G343 Turbocharged - Aftercooled

G353

G375 Turbocharged - Aftercooled

G379

G397 Turbocharged - Aftercooled

G398

G399 Naturally Aspirated

G399 Turbocharged - Aftercooled

Adjusting The Fuel-Air Ratio

The fuel-air ratio for the engine is adjusted by changing the gas differential. Too much gas permits a rich mixture and not enough gas makes a lean mixture. Either too rich or too lean a mixture will cause a loss of power. (Propane is more sensitive to gas differential than is natural gas.) The fuel air ratio can be checked by connecting one of the differential pressure gauges to the fuel-air line as shown below.

The correct differential pressure setting will vary depending upon the heat value of the gas obtained from the gas company as shown on pages 39 and 40.

The values given in the chart on page 40 are high heat values (HHV). This is the most common value given by the gas companies. The BTU content that is more important is the low heat value (LHV). When natural gas is burned, carbon dioxide and water are formed. Approximately one pound of water is formed for every 10 cubic feet of natural gas burned. This water is instantly turned into steam in the cylinder. The heat needed to vaporize the water is lost to the engine. The result is the LHV of the fuel. Usually, the LHV is 10% less than the HHV for natural gas. When obtaining the heat values from the gas companies, try to get the LHV, and use the chart on page 39. If the LHV is not obtainable, use the HHV and the chart on page 40.

If it is necessary to adjust the gas pressure regulator, refer to the Engine Data Sheet (EDS) 65.3, Form No. LE022005, available from the Industrial Sales Division.


LOWER HEATING VALUE (X100 BTU/FT3


HIGHER HEATING VALUE (X100 BTU/FT3)

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