C-10 and C-12 Truck Engines Caterpillar

Either too much fuel or not enough fuel for combustion can be the cause of a problem in the fuel system. Work is often done on the fuel system when the problem is really with some other part of the engine. Finding the source of the problem is difficult, especially when smoke comes from the exhaust. When noticeable smoke rises from the exhaust, this problem can be caused by a damaged unit injector. This unusual smoke can also be caused by one or more of the reasons that follow:

• Not enough air for good combustion

• An overload at high altitude

• Oil leakage into combustion chamber

• Not enough compression

• Incorrect fuel injection timing

• Cold engine operation

• Low cetane fuel

Illustration 1	g00430179
Fuel system components (1) Fuel filter base (2) Fuel line from ECM (3) Fuel priming pump (4) Fuel filter (5) ECM

Illustration 2	g00430180
Fuel system components (6) Fuel supply and return manifold (7) Fuel transfer pump (8) Fuel line (fuel transfer pump to ECM)

Fuel System Inspection

A problem with the components that send fuel to the engine can cause low fuel pressure. This can decrease engine performance.

1. Check the fuel level in the fuel tank. Make sure that the vent in the cap is not filled with dirt.

2. Check all fuel lines for fuel leakage. The fuel lines must be free from restrictions and damaged bends. Verify that the fuel return line is not collapsed.

3. Install a new fuel filter.

4. Remove any air that may be in the fuel system. Refer to Testing and Adjusting, "Procedure for Fuel Priming" for more information.

Fuel Transfer Pump

When the engine is operating at the rated rpm and load condition, the fuel transfer pump moves the fuel through the following components:

• ECM

• Fuel filter base

• Fuel supply and return manifolds

An orificed valve in the return fuel manifold restricts fuel flow. A pressure regulator valve is in the transfer pump. The normal fuel pressure is 630 kPa (91 psi) at rated rpm.

If the fuel pressure is low 517 kPa (75 psi) or less, stop the engine. Replace the fuel filter. Check the fuel lines in order to ensure that the fuel lines are not plugged. Make sure that the fuel lines are not damaged.

Start the engine and again check the fuel pressure. If the fuel pressure is still low, check the fuel regulator valve in the fuel transfer pump.

Stop the engine if the fuel pressure is at 690 kPa (100 psi) or above 690 kPa (100 psi). Remove the orificed valve from the connector. The valve is directly behind the return line fitting. Check for debris that is plugging the orifice holes near the tip. If the orifice holes are plugged, flush any remaining debris from the return passage. Then check the source of debris. If the orifice holes are not plugged, check for a plugged return fuel line. If the return fuel line is not plugged, check the regulator valve in the fuel transfer pump for debris or for rust.

Fuel Pressure

Table 1

Required Tools
Part Number	Part Name	Quantity
1U-5470	Engine Pressure Group	1

Illustration 3	g00293196
1U-5470 Engine Pressure Group

Refer to Special Instruction, SEHS8907, "Using The 1U-5470 Engine Pressure Group".

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Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. Clean up fuel spills immediately.

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NOTICE
Keep all parts clean from contaminants. Contaminants may cause rapid wear and shortened component life.

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NOTICE
Care must be taken to ensure that fluids are contained during performance of inspection, maintenance, testing, adjusting and repair of the product. Be prepared to collect the fluid with suitable containers before opening any compartment or disassembling any component containing fluids. Refer to Special Publication, NENG2500, "Caterpillar Tools and Shop Products Guide" for tools and supplies suitable to collect and contain fluids on Caterpillar products. Dispose of all fluids according to local regulations and mandates.

1. Use the following procedure to measure the fuel pressure after the secondary filter:

   Note: Fuel pressure readings near the fuel supply manifold have pressure spikes. The pressure spikes are caused by excess fuel that is returning to the fuel system from the injectors. Excessive needle movement at the gauge may be present. Connect the gauge with a section of suitable hose. The air in the hose absorbs the spikes. This gives an average reading and a steady needle. Keep the gauge above the measuring point.

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   Illustration 4	g00824204
   Standard Secondary Fuel Filter Base (1) Proper Port

   1. If the fuel filter base is mounted on the fuel supply manifold, install the 1U-5470 Engine Pressure Group into port (1). This port is the proper test port.
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   Illustration 5	g00597254
   Type 1 Fuel Filter Base (Remote Mount) (3) Fuel Manifold Adapter (4) Fuel Filter Base (Remote Mount) (5) Test Port

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   Illustration 6	g00825982
   Type 2 Fuel Filter Base (Remote Mount) (2) Fuel Filter Base (Remote Mount) (3) Test Port (4) Fuel Manifold Adapter (5) Return Fuel Port

   2. If the fuel filter base is a remote mount, install the 1U-5470 Engine Pressure Group into port (4) that is on the top of the fuel filter base.

   3. Adjust the engine speed to 1800 rpm with no load.

   4. The fuel pressure should be 586 kPa (85 psi) nominal. Record the pressure.

   5. If excessive pressure is found, check the conditions that are listed under the "High Fuel Pressure" heading.

2. Use the following procedure to measure the fuel pressure before the secondary filter:
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   Illustration 7	g00597849
   Standard Fuel Filter Base (6) Port

   1. If the fuel filter base is mounted on the fuel supply manifold, install the 1U-5470 Engine Pressure Group into port (6) .
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   Illustration 8	g00597851
   Secondary Fuel Filter Base (Remote Mount) (7) Fuel Line Fitting

   2. If the secondary fuel filter base is a remote mount, remove the fuel line. Install a tee at fuel line fitting (7). Reinstall the fuel line. Install the 1U-5470 Engine Pressure Group into the empty tee connection.

   3. Adjust the engine speed to 1800 rpm with no load.

   4. If the pressure is more than 35 kPa (5 psi) above the reading recorded after the secondary filter, the secondary filter is plugged or the priming pump is plugged.

   5. Replace the secondary filter and check the pressure again. Inspect the priming pump for debris if the pressure remains more than 35 kPa (5 psi) above the reading recorded after the secondary filter. Replace the priming pump, if necessary.

   6. If fuel pressure is low both before the secondary fuel filter and after the secondary fuel filter, the primary fuel filter is suspect. If the primary filter has not been replaced yet, change the filter and check the pressure again.

   7. If the pressure is still low, continue to step 3.

3. Use the following procedure to check the output of the fuel transfer pump:

   1. Remove the return fuel line. Remove the return fuel line fitting. This return fuel line fitting is located on the standard secondary fuel filter base. The return fuel line fitting is located on the fuel manifold adapter if the secondary fuel filter base is a remote mount.

   2. Install the 1U-5470 Engine Pressure Group into the port that contained the return fuel line fitting.

   3. Adjust the engine speed to 600 rpm with no load.

   4. The fuel pressure should be 690 kPa (100 psi) to 724 kPa (105 psi).

   5. If the fuel pressure is within the specified range, proceed to step 4.
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   Illustration 9	g00597852
   Fuel Transfer Pump (Side View) (8) Access plug

   6. If the pressure is less than 655 kPa (95 psi), the fuel transfer pump is weak. The pressure regulating valve in the pump may be stuck or worn. The pressure regulating valve is located under access plug (8). Remove the access plug. Remove the pressure regulating valve, the spring, and the pin. Replace the fuel transfer pump if the pressure regulating valve is significantly worn and no debris accumulation is found. If debris accumulation is found, clean the valve assembly and reinstall the valve assembly. Reinstall access plug (8) .

   7. Check the fuel pressure again. Replace the fuel transfer pump if the fuel pressure still measures less than 655 kPa (95 psi). The fuel transfer pump is operating properly if the fuel pressure measures at least 690 kPa (100 psi) to 724 kPa (105 psi).

   8. Once the fuel transfer pump has been confirmed as properly operating, check the fuel pressure again at the secondary fuel filter base. Refer to step 2. If the fuel pressure is not at the nominal specification, continue to step 4.

4. Use the following procedure to inspect the return fuel pressure regulating valve:
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   Illustration 10	g00598160
   Type 1 Standard Secondary Fuel Filter Base (9) Return fuel pressure regulating valve (10) Spring

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   Illustration 11	g00598162
   Type 1 Fuel Manifold Adapter (9) Return fuel pressure regulating valve (10) Spring

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   Illustration 12	g00717659
   Type 2 Fuel Filter Base

   Note: The fuel filter base (Type 2) that is used in Illustration 12 does not contain a return fuel pressure regulating valve. If the fuel filter base (Type 2) is used on your engine, proceed to step 5.

   1. Return fuel pressure regulating valve (9) is located behind the return fuel line fitting. Remove the return fuel pressure regulating valve (9) and remove spring (10) .

   2. Inspect return fuel pressure regulating valve (9) for wear. Replace the valve if the taper exceeds 0.13 mm (0.005 inch).

   3. Inspect the return fuel line fitting. The return fuel pressure regulating valve (9) shifts against the return fuel line fitting. The movement of the valve will cause the return line fitting to wear over time. Replace the fitting if there is evidence of significant wear.

   4. Reinstall the spring (10) and the return fuel pressure regulating valve (9). Reinstall the return fuel line fitting and reinstall the return fuel line.

   5. Check the fuel pressure again at the secondary fuel filter base. Refer to step 2. If the fuel pressure is not up to 586 kPa (85 psi), then perform step 5. If the primary filter is sized correctly and the fuel lines are sized correctly, replace the secondary fuel filter base. If the secondary fuel filter base is a remote mount, replace the fuel manifold adapter.

5. Use the following procedure to measure the vacuum at the primary filter:

   1. Adjust the engine speed to 1800 rpm with no load.

   2. Measure the vacuum at the outlet of the primary filter.

   3. The vacuum should be 10.14 kPa (3 in Hg) to 13.52 kPa (4 in Hg). If the vacuum is more than 30.42 kPa (9 in Hg), measure the vacuum at the inlet of the primary filter. The differential across the primary filter should be less than 3.38 kPa (1 in Hg) with a new filter installed. If the differential is higher by more than 3.38 kPa (1 in Hg), the filter is undersized. The filter should be rated at 341 L (90 US gal) per hour. If the filter is sized correctly, ensure that the fittings and lines are correctly sized. The fuel lines should be 12.7 mm (0.5 inch). Also check for debris in the fuel tank that may be plugging the supply tube.

Procedure for Fuel Priming

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Fuel leaked or spilled onto hot surfaces or electrical components can cause a fire. To help prevent possible injury, turn the start switch off when changing fuel filters or water separator elements. Clean up fuel spills immediately.

Illustration 13	g00430181
Typical example (1) Plug (2) Priming pump

If the fuel system runs out of fuel or if air is introduced into the fuel system, the following procedure may be followed.

Note: The fuel system does not need to be primed after you change only the fuel filter. The engine will remain running after you start the engine with a dry filter.

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NOTICE
Do not allow dirt to enter the fuel system. Thoroughly clean the area around a fuel system component that will be disconnected. Fit a suitable cover over disconnected fuel system component.

1. After you add fuel to the fuel tank, remove plug (1) .

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NOTICE
Use a suitable container to catch any fuel that might spill. Clean up any spilled fuel immediately.

2. Unlock and operate hand priming pump (2) in order to pump fuel into the fuel system. This will also purge air from the fuel system. Stop operating the hand priming pump when fuel appears at the port.

3. Install plug (1). Clean up any spilled fuel immediately.

4. Operate the hand priming pump until you feel a strong pressure on the pump and until you hear a click from the fuel filter base. This pressurizes the system with approximately 345 kPa (50 psi). This greatly reduces the cranking time that is needed to start the engine.

5. Push in and hand tighten the priming pump plunger.

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NOTICE
Do not crank the engine continuously for more than 30 seconds. Allow the starting motor to cool for two minutes before cranking the engine again.

6. Crank the engine as soon as possible after you pressurize the system. The engine should start within 15 seconds.

   If the engine does not start after 30 seconds, stop cranking the engine. Repeat Steps 4 through 6.

Unit Injector Adjustment

Illustration 14	g00481504
Injector Mechanism (1) Rocker arm (2) Adjusting screw (3) Locknut

To make an adjustment to the unit injectors on cylinders 3, 5, and 6 use the following procedure:

1. Put the number 1 piston at the top center position on the compression stroke. Refer to Systems Operation/Testing and Adjusting, "Finding Top Center Position For No. 1 Piston".

2. Turn the unit injector adjusting screw (2) clockwise until contact is made with the unit injector.

3. Turn the unit injector adjusting screw through 180 degrees in a clockwise direction.

4. Hold the adjusting screw in this position and tighten the locknut (3) to a torque of 55 ± 10 N·m (41.0 ± 7.0 lb ft).

5. To make an adjustment to the unit injectors on cylinders 1, 2, and 4, remove the timing bolt. Turn the flywheel by 360 degrees in the direction of the engine's rotation. The engine rotates in a counterclockwise manner. This will put the number 1 piston at the top center position on the exhaust stroke.

6. Repeat 2 through 4.

7. Remove the timing bolt from the flywheel after all of the unit injector adjustments have been made. Reinstall the timing cover.

Checking Engine Cylinders Separately

Table 2

Required Tools
Part Number	Part Name	Quantity
164-3310	Laser Infrared Thermometer	1

When the engine runs at low idle, the temperature of an exhaust manifold port can be an indication of the condition of a unit injector. Low temperature at an exhaust manifold port is an indication of no fuel to the cylinder. This could be caused by an inoperative unit injector. Extra high temperature at an exhaust manifold port can be an indication of too much fuel to the cylinder. This is caused by a malfunctioning unit injector.

Use the 123-6700 Laser Infrared Thermometer to check exhaust temperature. The Operator's Manual, "Laser Infrared Thermometer II with laser Sighting" for the 123-6700 Laser Infrared Thermometer gives the complete operating and maintenance instructions for the tool.

Timing of the Timing Reference Ring and the Front Gear Group

Illustration 15	g00430184
Front gear group (1) Camshaft gear and timing reference ring (2) Timing marks (3) Idler gear (4) Crankshaft gear

The basis for correct fuel injection timing and valve mechanism operation is determined by the timing reference ring and the alignment of the front gear group. The timing reference ring is located on the end of the camshaft. The timing reference ring is used to measure crankshaft rotation. During installation of the front gear, the timing marks (2) on the idler gear (3) must be in alignment with the timing marks on the crankshaft gear (4) and the timing marks on the camshaft gear (1) .

Refer to Disassembly and Assembly, "Front Gear Group" for a complete removal and installation procedures of the front gear group.

Note: If timing reference ring (1) is installed backward the engine will not start.

Check for proper alignment of the camshaft gear and timing reference ring (1) on the camshaft assembly. Inspect the key between the timing reference ring and the camshaft gear. Check the teeth on the timing ring. The teeth should not be defaced. The teeth should have sharp clean edges and the teeth should be free of contaminants.

Note: The electronic injection timing must be calibrated after reassembly of the front gear train. Refer to the Electronic Troubleshooting, "Electronic Injection Timing" topic for the proper procedure to calibrate the electronic injection timing.

Finding the Top Center Position for No. 1 Piston

Table 3

Required Tools
Part Number	Part Name	Quantity
9S-9082	Engine Turning Tool	1

Illustration 16	g00481516
Top center position (1) Bolts (2) Cover (3) Flywheel Housing

1. Remove two bolts (1) and remove cover (2) from flywheel housing (3) in order to open the turning hole.

2. Put one 6V-5219 Bolt (1) in the timing hole. The timing hole is located approximately 127 to 152 mm (5.0 to 6.0 inch) above the turning hole in the flywheel housing. Use the 9S-9082 Engine Turning Tool and a 1U-7115 Reverse Ratchet to turn the engine flywheel. Turn the flywheel in the direction of engine rotation. The direction of engine rotation is counterclockwise, as the engine is viewed from the flywheel end. Turn the flywheel until the timing bolt engages with the threaded hole in the flywheel.

   Note: If the flywheel is turned beyond the point of engagement, the flywheel must be turned in the direction that is reverse of normal engine rotation. Turn the flywheel by approximately 30 degrees. Then turn the flywheel in the direction of normal rotation until the timing bolt engages with the threaded hole. This procedure removes the play from the gears when the No. 1 piston is at the top center position.

3. Remove the front valve mechanism cover from the engine.

4. The inlet and exhaust valves for the No. 1 cylinder are fully closed if No. 1 piston is on the compression stroke and the rocker arms can be moved by hand. If the rocker arms cannot be moved and the valves are slightly open, the No. 1 piston is on the exhaust stroke.

   Note: When the actual stroke position is identified, and the other stroke position is needed, remove the timing bolt from the flywheel. Then turn the flywheel by 360 degrees in the direction of normal engine rotation and reinstall the timing bolt.

Checking and Calibrating the Electronic Injection Timing With the Electronic Service Tool

Refer to Troubleshooting, "Electronic Injection Timing" for the proper procedure to calibrate the electronic injection timing.