3126B Truck Engine Caterpillar

Illustration 1	g00608514
Right side view (1) Lifting eye (2) Engine crankcase breather (3) Turbocharger (4) Oil filler (5) Water temperature regulator housing (6) Belt tensioner (7) Water drain plug (8) Crankshaft vibration damper (9) Oil filter (10) Jacket water pump

Illustration 2	g00608515
Left side view (11) Oil filler (12) Lifting eye (13) Fuel filter (14) Fuel priming pump (if equipped) (15) Oil level gauge (typical example) (16) Electronic Control Module (ECM) (17) Air compressor (18) Cylinder head grounding stud (19) Oil drain plug

The 3126B engines are in-line six cylinder arrangements. The engine has a firing order of 1-5-3-6-2-4. The engine's rotation is counterclockwise when the engine is viewed from the flywheel end of the engine. The engine utilizes a turbocharger and an air-to-air aftercooler. The engines have a bore of 110 mm (4.3 inch) and a stroke of 127 mm (5.0 inch). The displacement is 7.25 L (442 in ³ ).

The hydraulic electronic unit injector system (HEUI) eliminates many of the mechanical components that are used in a pump-and-line system. The HEUI also provides increased control of the timing and increased control of the fuel air mixture. The timing advance is achieved by precise control of the unit injector timing. Engine rpm is controlled by adjusting the injection duration. A special pulse wheel provides information to the Electronic Control Module (ECM) for detection of cylinder position and engine rpm.

The engine has built-in diagnostics in order to ensure that all of the components are operating properly. In the event of a system component failure, the operator will be alerted to the condition via the check engine light that is located on the dashboard. An electronic service tool can be used to read the numerical code of the faulty component or condition. Also, the cruise control switches can be used to flash the code on the check engine light. Intermittent faults are logged and stored in memory.

Starting The Engine

The engine's ECM will automatically provide the correct amount of fuel in order to start the engine. Do not hold the throttle down while the engine is cranking. If the engine fails to start in twenty seconds, release the starting switch. Allow the starting motor to cool for two minutes before the starting motor is used again.

Cold Mode Operation

The ECM will set the cold start strategy under the following condition:

• the engine oil temperature is below 18 °C (64 °F).

Under this condition, low idle rpm will be increased to 1000 rpm. The engine's power will also be limited.

Cold mode operation will be deactivated after any one of the following conditions:

• the engine oil temperature is above 18 °C (64 °F).

• twelve minutes of running in cold mode

• vehicle speed above 2 mph

Note: Under certain fault conditions of temperature sensors, cold mode will be disabled after 2 minutes.

The elevated idle of 1000 rpm of cold mode operation will be deactivated after any one of the following conditions:

• depressing the service brake

• depressing the throttle

• depressing the clutch

In automatic transmissions, the cold mode operation will be deactivated after any one of the following conditions:

• placing an automatic transmission in gear from the NEUTRAL position

• placing an automatic transmission in gear from the PARK position

The cold mode operation may ramp slowly back to 1000 rpm under any of the following conditions:

• the temperature conditions still exist.

• an automatic transmission is not in gear.

Cold mode operation varies the fuel injection amount for white smoke cleanup. Cold mode operation also varies the timing for white smoke cleanup. The engine operating temperature is usually reached before the walk-around inspection is completed. The engine will idle at the programmed low idle rpm in order to be put in gear.

After the cold mode is completed, the engine should be operated at low rpm until normal operating temperature is reached. The engine will reach normal operating temperature faster when the engine is operated at low rpm and low power demand.