Fuel System and Fuel Ratio Control Test Procedure{1264, 1278} Caterpillar

Introduction

This instruction outlines the procedure to troubleshoot response and low power problems.

Response is the engine's ability to accelerate, under load, to its rated horsepower. Poor response can result from problems with the governor, the fuel ratio control or the shutoff system.

Low power is the engine's inability to produce its rated horsepower. Low power can result from problems with the fuel pump, the governor setting, the shutoff system or the other fuel flow components, or with the engine application.

A new procedure for confirming and isolating response problems has been developed.

The new procedure will test the response functions of the governor, the fuel ratio control and the shutoff system. It will verify whether or not the response functions are within specifications. If they are not within specifications, the procedure will isolate the cause of the problem.

This new procedure also will check governor settings, fuel ratio control settings, full load measurements and governor servo measurements. These checks are completed without disassembly of the governor or the fuel ratio control, thereby eliminating the need to break the governor seal if no readjustment is required.

A dealer-fabricated tester (drawing FT1906) is needed for this procedure. This tool will check the governor, the fuel ratio control and servo. It will permit testing with or without a dynamometer. The FRC tests can be obtained below full load rpm, but full load is necessary for a complete engine system check.

The following chart lists all the components of the FT1906 Fabricated Tester. All components, except for the tubing and the bulb, are available from Caterpillar Inc. The tubing and the bulb can be purchased at a medical supply store. Figures 1 and 2 show how to assemble the tester.

FIGURE 1 Fabricated Tester

FIGURE 2 Fabricated Tester

Troubleshooting Procedure for Engine Response, Fuel Ratio Control Governor

Connect the fabricated tester to the fuel control and to the inlet manifold. Figure 2 shows the proper connections. Install the 6V4060 Engine Set Point Indicator Group or a continuity light. A commercially available circuit testing flashlight is recommended.

Remember, two points during the procedure. For constant repeatable readings under load, the engine must be at full throttle. If full fuel position is not used, incorrect readings or no readings will result. Most fuel ratio controls allow full fuel position at or above 381 mm (15") Mercury (Hg) or 52 kPa (7.5 psi) for Current Scroll Fuel System (CSFS). The travel test in Full Fuel Test (No Load Test) will confirm this point. Response or power problems at greater manifold pressures are not usually caused by the fuel ratio control.

A chart is supplied in the back of this instruction for recording the tested values. It can be used by itself once you are familiar with the procedure. This chart, SEHS8499-01, is available in pads of 50.

Diaphragm Leakage Test (No Load Test)

1. Turn the tester valve so that manual air pressure can be applied.

2. With the engine stopped, pressurize the ratio control to 70 kPa (10 psi). Allowable leakage in 30 seconds is 20 kPa (3 psi). If leakage is greater, check for leaks or repair the fuel ratio control. If it passes, release the pressure and continue below.

Full Fuel Travel and Shutoff Linkage Test (No Load Test) - Either of these two methods is acceptable

"0" pressure to the Fuel Ratio Control (FRC).

1. Turn the ignition switch on, but do not start the engine or move the throttle.

2. Hold the shutoff lever or shaft with one hand and slowly advance the throttle to its full position.

NOTE: Interference exists if any contact with the shutoff linkage is felt. The shutoff lever must have some free movement. In most cases, continuity should occur before 1/2 full fuel position.

* Any contact will cause power and response problems at high boost when manifold pressure is greater than 381 mm (15") Mercury (Hg) or 52 kPa (7.5 psi).

Static Full Throttle Test (No Load Test)

1. Move tester to operator's station.

2. Gradually move the throttle to its full load position. Continuity should occur before 1/2 full throttle.

If the light does not turn on:

* Check the linkage travel.* Check the shutoff solenoid adjustment.* Check the operation of the governor circuit indicator.* Look for any other restrictions.

If the light turns on, continue below.

Dynamic Full Fuel Movement Test (No Load Test)

"0" pressure to the FRC.

1. Start the engine.

2. Move the throttle to full fuel position, and release. Perform this sequence twice. The light should turn on.

If the light does not turn on:

* Check the fuel ratio control for premature activation.* Check for incorrect settings.* Perform the Full Fuel Travel and Shutoff Linkage Test (No Load Test) again.

If the light turns on, continue below.

Activation Test for Fuel Ratio Control (No Load Test)

1. Turn the tester valve so that manual air pressure can be applied. Maintain 900 ± 100 rpm.

2. Apply 35 kPa (5 psi) for five seconds, then release the pressure.

3. Move the throttle to its full fuel position and release it. Perform this twice. The light should not come on.

If the light is on:

* Check the ratio control setting.* Check the continuity circuit to insure that it is functioning properly.* Repair and/or adjust the FRC as needed; it is not activating.

If the light does not turn on:

* The ratio is activated and acceptable.* Continue additional testing below.

Full Fuel Test (No Load Test)

1. Apply 25 kPa (4 psi) to the fuel ratio control.

2. Move the throttle to its full fuel position, and release it.

3. Increase the pressure using increments of 3.5 kPa (0.5 psi).

4. Again, move the throttle to its full fuel position, then release it.

Do this until the continuity light, or the "lug" light on the set point indicator turns on.

5. Record the pressure reading and continue below.

Load Test (Load Required)

1. Turn the tester valve to allow manifold boost readings.

2. With the engine speed at 1500 rpm and at low boost, 20 kPa (3 psi) or less, quickly load it with full load and full fuel. When the "lug" or continuity light turns on, record the boost reading.

NOTE: An activated light indicates full rack travel. The engine must have a load that requires full fuel. Loads requiring less than full fuel will not give consistent readings.

* The boost reading should be within ± 1/2 psi of the reading obtained in Full Fuel Test (No Load Test). Repeat this test sequence twice. Also, record the set point rpm, maximum boost, and horsepower if on a dyno.* If the readings were consistent, ± 3.5 kPa (0.5psi) proceed to Governor Response Test below.* If erratic readings were obtained, either the ratio control, governor, or the test is not operating smoothly. Continue below for additional testing.

Governor Response Test (Load Required) - Test under same conditions as used for Load Test (Load Required). This response can also be observed in the previous test.

1. Turn the tester valve so that manual air pressure can be applied.

2. Apply 70 kPa (10 psi). This will move the fuel ratio control away from the rack control position. While under load, move the throttle to its full fuel position. Observe how fast continuity is obtained.

* If it takes more than two seconds to obtain continuity, governor response is unsatisfactory. Inspect the external attachments on the governor for interference.* If continuity is obtained in less than two seconds, governor response is satisfactory. Generally, continuity in less than two seconds will be acceptable.* If the above eight tests checked okay, the fuel ratio control and the governor are operating satisfactorily. The test is complete.

NOTE: The above tests have verified the response functions. They did not check for correct adjustments of the ratio control and the fuel settings.

Governor, Fuel Ratio Control, Servo Response, Travel Test

With the engine stopped:

1. Do not remove the fuel ratio control or the solenoid. Install the necessary fuel setting and measurement tools. Record and compare the static fuel setting to the setting on the valve cover.

2. Move the throttle to its full forward position. Record the full governor setting at the full fuel position. This is the "full torque" reading; it is the compressed torque spring and internal governor clearances.

With the engine running:

1. Apply 35 kpa (5 psi) for ten seconds. Release the pressure. This should activate the ratio control.

2. Move the throttle to its full fuel position. Release the throttle, and record the dynamic ratio control setting. Continue below for additional testing.

Governor Servo Movement Test (No Load Test)

This test is performed with the engine running.

NOTE: The servo should provide 0.36mm (.020" ± .004") additional travel.

Apply 70 kPa (10 psi) to the ratio control. Move the throttle to its full fuel position and release. Record the dial indicator reading.

* If the indication is 0.36mm (.020" ± .004") more than the "full torque" reading obtained in the Governor, Fuel Ratio Control, Servo Response, Travel Test, the governor, the governor servo, and the rack is attaining full travel. No further testing is necessary. The FRC, governor and linkage are okay.* If the indication is not 0.36mm (.020" ± .004") more than the static "full torque" reading the governor or servo movement is unsatisfactory.* This indicates that interference exists or there is an internal problem with the governor, or internal linkage. The shutoff system may still require inspection. Continue below for additional testing.

Governor Servo and Shutoff Circuit Test (No Load Test)

1. Remove the fuel ratio control and install a 4N5656 Plate.

2. Record the static "full torque" setting. Compare this indication with the "full torque" reading obtained in the Governor, Fuel Ratio Control, Servo Response, Travel Test. It should be the same.

3. Start the engine. Move the throttle to its full fuel position and release. Record the setting and compare it to the reading obtained in the Governor Servo Movement Test (No Load Test).

* If the dynamic movement is the same, the ratio control is not the cause.* If more than 0.25mm (.010") difference exists, check for shutoff interference or internal governor linkage problems.* If slow governor response exists, check for restricted rack movement. Also, check for other governor problems. (No specific repair procedures are available.)* If all systems have checked out properly, the problems are not within the engine. The problems most likely exist in the vehicle or in the application.