for a fault in other parts of the engine; damage to the engine will result.
When you check the fuel pump on the engine, remove the pipe plug from the pump shutoff valve and connect the pressure gauge. At the governed speed (just before the governor cuts in), maximum manifold pressure should be obtained. If the manifold pressure is NOT within specified limits, adjust for maximum manifold pressure by adding or removing shims from under the nylon fuel adjusting plunger in the bypass valve plunger. Be careful you do not lose the small lock washer that fits between the fuel adjusting plunger and the plunger cap.
To check the suction side of the pump, connect the suction gauge to the inlet side of the gear pump. The valve in the pump, if properly adjusted, should read 8 inches on the gauge. When the inlet restrictions reaches 8.5 to 9 inches, change the fuel filter element and remove any other sources of restriction. The engine will lose power when the restriction is greater than 10 to 11 inches.
Always make the above checks on a warm engine. Also, operate the engine for a minimum of 5 minutes between checks to clear the system of air.
If the pump manifold and suction pressures are within specified limits and there is still a loss of power, you should check the injectors.
Carbon in the PT injector metering orifices restricts the fuel flow to the injector cups, which results in engine power loss. Remove the carbon from the metering orifices by reverse flushing; it should be performed on a warm engine. To remove carbon, perform the following steps:
1. Loosen all injector adjusting screws one turn from the bottom or one and one-eighth turns from the set position. Lock with the jam nut after completing the required turns.
2. Start the engine and accelerate with maximum throttle from idling to high-10 to 15 times.
3. Readjust the injectors to their standard setting.
The engine will be difficult to start with the loose injector setting; it will smoke badly and will be sluggish. If the injector adjusting screws are loosened, the meter orifice will not be closed during injection. Extremely high injection pressure will force some of the fuel to backflow through the orifice and should remove carbon deposits. If this method is not effective, remove the injectors for cleaning.
When working on the PT fuel system of a turbocharged Cummins engine, you may find an aneroid control device. This device creates a lag in the fuel system so that its response is equivalent to that of the turbocharger, thus controlling the engine exhaust emissions (smoke level).
WARNING The aneroid is an emissions control device. Removing it or tampering with it is in direct violation of state and federal vehicle exhaust emissions laws.
During troubleshooting of the fuel system, you should check the aneroid according to the manufacturer's specifications.
If you determine that the fuel pump (fig. 5-34) must be removed from the engine, take the following precautions:
Make sure the shop area is clean.
Use clean tools.
Good cleaning practices are essential to good quality fuel pump repair. Take special care when the PT fuel pump, which is made of a lightweight aluminum alloy, is disassembled. Use proper tools to prevent damage to machined aluminum surfaces, which are more easily damaged than parts made of cast iron.
Before disassembling the unit, try to determine what parts need replacement.
After you place the fuel pump on the holding device, place the device in a vise and disassemble the pump. Follow the procedures given in the manufacturer's maintenance and repair manuals.
Now that the pump has been disassembled, you should clean and inspect all parts. Do not discard parts until they are worn beyond reasonable replacement limits. The PT fuel pump parts will continue to function long after they show some wear. Parts that are worn beyond reasonable replacement limits must not be reused. From experience you know reasonable replacement limits. Reuse all those parts that will give another complete period of service without danger of failure.Continue Reading