1989-1993 Cummins® 12-Valve Engine Fuel System Troubleshooting

1989-1993 Cummins® Diesel Engine Fuel System Troubleshooting

If the engine won't start, here are some recommendations:

• Bleed the air out of the system

If you are starting your Cummins for the first time, it is required to “bleed” the air out of the injector lines by loosening the injector line nut just enough to allow fuel and air to escape the line while you are cranking the engine. It is usually required to do at least 3 injector lines. The best way to do this is by tightening the line nut while you are still cranking the engine. This is also a good way to verify that the injector pump’s shut down solenoid is allowing fuel to the injector. If your supply fuel line is loose, it is possible to draw air into the fuel system at that point, so if you suspect you are not getting rid of the air in the system check your supply line connections. These engines should have between 7-15 PSI of lift pump fuel pressure.

• If there is good supply pressure and fuel at injector

If this is the case and you are fairly certain there is no more air in the system, the injector pump may be weak or have incorrect injector pump timing. You may especially suspect this kind of problem if you have never heard the engine run before or if you replaced the injector pump.

• If there is good supply pressure but no fuel at injector

In this situation, it's likely that the shut down solenoid is not working properly. The shut down solenoid is shown inside the red circle in the picture below. These can be removed from the injector pump and inspected. There is a small plunger that can break or get stuck.

• If there is poor supply pressure

In this situation, the lift pump may be bad, or possibly restricted, or have leaky supply lines. If you have never ran the engine before, or the injector pump has been worked on, check the return line banjo bolt. This is a special banjo bolt with an orifice hole that regulates the fuel pressure inside the injector pump. If you have a full flow banjo bolt in this port, your lift pump pressure will be too low. 

If after trying these steps the engine in your conversion project still is having starting or fuel system issues, please Contact Us.