1674 DIESEL TRUCK ENGINE Fuel System Caterpillar

Fuel System
1.1. Fuel Injection Equipment

CARE OF THE FUEL SUPPLY: Too much emphasis cannot be placed on the importance of using only clean diesel fuel. It is important to buy clean fuel and keep it clean. The best fuel can be rendered unsatisfactory by inadequate storage facilities or careless handling.

Effort should be constantly expended to prevent contamination of the fuel. An important step is to reduce the number of times the fuel must be handled. When the fuel can be delivered by the distributor to storage tanks and then pumped from the storage tank to the diesel fuel tank, the handling is reduced to a minimum.

CARE OF THE DIESEL FUEL TANK: Fill the fuel tank at the end of the day, because the incoming fuel will drive out the moistureladen air and prevent condensation.

DRAINING FUEL TANK SEDIMENT ACCUMULATION: Open the drain cock and drain off any sediment or water which may accumulate in the fuel tank before starting the engine. In temperatures below freezing, drain shortly after the truck has stopped to prevent water freezing in the bottom of the tank and other low points in the system.

FUEL FILTERING SYSTEM: As either the primary fuel filter element or the final fuel filter element gradually become clogged with foreign material, lack of horsepower will be noticed and the position of the fuel gauge indicator will work back from the original position in the NORMAL (green or approximately 30 PSI) range to the OUT (red or approximately 23 PSI) range. Every 10,000 miles or when the indicator shows in the OUT (red) range, the metallic primary fuel filter element (if equipped) should be removed and washed. If the indicator still shows in the OUT (red) range, the final filter element should be replaced with a AVSpare filter element. Other make fuel filters may not meet filtering or capacity requirements. See the topics, PRIMARY FUEL FILTER and FINAL FUEL FILTER.

PRIMARY FUEL FILTER: To remove the filter element, stop the engine and shut off the diesel fuel tank valve. Loosen the nut on the filter cover and lower the filter case. Remove the element and wash in clean solvent or diesel fuel. Reinstall the element.


FINAL FUEL FILTER ELEMENT: The filter element collects and holds contaminants and cannot be washed or otherwise restored. To remove the used filter element, proceed as follows:

1. Stop the engine and close the diesel fuel line valve (if equipped).
2. Unscrew and remove filter.
3. Clean the gasket sealing surface on the filter base.


Do not pour fuel into the new filter elements before installing. Prime the system as instructed in the topic, PRIMING THE FUEL SYSTEM.

4. Lubricate the filter gasket with clean diesel fuel.
5. Tighten the filter by hand, only tight enough to prevent leaks. (Do not overtighten.)
6. Prime the fuel system. Refer to the topic "PRIMING THE FUEL SYSTEM"


KEEP A NEW FUEL FILTER ON HAND: An extra filter should be kept on hand for replacement. Always keep the filter wrapped in its original carton to insure against dust and dirt accumulation which will shorten the life of the filter or may cause damage to the fuel injection equipment.

PRIMING THE FUEL SYSTEM: Any time the fuel flow is broken and air is allowed to get into the fuel system, the system must be primed. If air is left in the lines, the fuel system may become air bound, resulting in inability to start the engine or the misfiring of one or more cylinders.


The fuel priming pump is mounted on the fuel filter housing as shown. If only the fuel filter is changed follow steps 1 through 5. If the fuel system is completely drained or if the engine has run out of fuel continue with steps through 10.

1. Check to see that the fuel line valve is open.
2. Open the fuel filter vent valve on the fuel filter housing.
3. Loosen the knob of the fuel priming pump.
4. Operate the pump plunger in and out until the flow of fuel from the vent valve is continuous and free of air bubbles.
5. Close vent valve.
6. Move governor control to the shut-off position and loosen fuel line nuts (one at a time) at the pump housing.
7. Operate priming pump until clear fuel flows from the fuel pump lines. Tighten fuel line nut.
8. Repeat for each fuel pump.
9. Lock the knob of the fuel priming pump to its original position.
10. Start the engine. If the engine does not run smoothly further bleeding may be necessary. With the engine running, open and close the fuel injection line nuts, one at a time, several times in succession to be sure all the air is bled from the system. Tighten fuel line nuts to 30 lbs.ft. (4,1 mkg). Do not overtighten.

Fuel Injection Equipment

When improper fuel injection is affecting engine operation, a systematic check should be made to determine the cause. The most likely cause is dirt or water in the fuel. Drain the sediment from the fuel tank. Check the fuel pressure gauge as mentioned in the topic, FUEL FILTERING SYSTEM. Replace the filter element if necessary. Then prime the fuel system until clean fuel reaches the fuel injection pumps. If the fuel system is air bound, priming the system will overcome the difficulty.

If the engine is running irregularly, smoking, or knocking, a fuel injection valve may not be spraying the fuel properly.

As the clearance between the plunger and the barrel of a fuel injection pump increases, due to wear, fuel leakage occurs. When the leakage increases to the point where insufficient fuel is injected into the cylinder, a loss of power is noticeable. With the loss of power, hard starting is also encountered.

TESTING FUEL INJECTION VALVES: Whenever an engine performs in such a manner that a fuel injection valve is suspected of causing trouble, test all fuel injection valves. To test the injection valves: Loosen the fuel injection line nut at the fuel injection pumps, one at a time, while the engine is running.


When a nut is loosened and the exhaust smoking is completely or partially eliminated and the irregularity in running is not affected, this identifies the probable location of a defective valve and a new one should be installed in that cylinder to definitely determine if the valve removed was defective.

Never wire brush or scrape a fuel injection nozzle assembly as this will damage the finely machined orifice. Your authorized dealer has the proper tools for cleaning and testing fuel injection valves.

REMOVE FUEL INJECTION VALVE: Clean dirt from around the valve cover and remove. Before removing an injection valve, clean the dirt from around the valve and line connections. Disconnect the lead wire from the glow plug.

Loosen the fuel injection line at camshaft housing and disconnect it from the valve. Immediately install plugs to prevent dirt from entering the fuel injection line. Remove the valve retainer nut and lift out the fuel injection nozzle assembly and body as a unit. If the fuel injection valve will not be immediately installed, caps should be put on the valve body to prevent dirt entering the valve assembly.



INSTALLING FUEL INJECTION VALVES: Before installation of a fuel injection valve, be sure the wrench is clean. Install the fuel injection valve in the following manner.

1. Screw the valve body into the fuel injection valve nozzle assembly only finger tight.


2. Insert the nozzle assembly and valve body as a unit into the precombustion chamber opening. Turning the body in a clockwise direction and at the same time pressing down will assure alignment of the serrations.
3. Install the retainer nut and tighten to a torque of 50 to 55 pounds feet to prevent leaks between the nozzle assembly and the nozzle assembly seats.


Do not over tighten. Use torque wrench.

4. Connect the fuel injection line and tighten the nuts.

FUEL INJECTION PUMPS: To check or replace fuel injection pumps, to check fuel injection timing, injection pump lifter setting, fuel rack setting and governor adjustments, it is recommended they be performed by an authorized dealer.

GOVERNOR: Check the engine high and low idle RPM at the first oil change period and every 50,000 miles or 1,000 service hours thereafter. Remove tachometer drive cable (or cap) from the tachometer drive housing at front of engine. Correct high idle RPM is 2505 ± 30 and low idle RPM is 650 ± 10. It is recommended this adjustment be made by an authorized dealer.

NOTE: Tachometers on the truck dash panel are usually not sufficiently accurate to check high and low idle engine RPM. Always use an accurately calibrated tachometer.

FUEL-AIR RATIO CONTROL: The fuel-air ratio control is a device to control the smoke emission of an engine during its operation when low inlet manifold pressure exists. Low inlet manifold pressure occurs during operation at low power output due to low engine speed or low torque output. During this type of operation the fuel-air ratio control regulates the maximum fuel injected into each cylinder. If the controlling diaphragm within the fuel-air ratio control should rupture, the fuel system will be restricted the same as it would be with low inlet manifold pressure. Slow engine response and low power may indicate a need for adjustment or repair. Authorized dealers are equipped with the necessary tools, personnel and procedures to perform these services.