Jeep Fuel Pump Problems
My 1998 Grand Cherokee is not starting and my fuel pump is running constantly. How do I fix these issues?
In most cases this happens when the PCM is down. This causes your vehicle not to start and your fuel pump to run constantly. There are a number of reasons that cause the PCM to fail. You should load test the power and ground as lost or weak power or ground can result in the PCM failing. The PCM could also fail if there is a short to voltage on the sensor ground circuit. To check the voltage you need to unplug the TPS or MAP sensor and check it on the black/light blue wire to ensure that there is no voltage. Another cause for the PCM to go down is a 5v reference circuit shorted to the ground. Unplug all the sensors on the 5v circuit, unplug the PCM and check the reference wire for resistance to ground. You will have to replace the PCM to resolve the issue.
Why does my 1993 Jeep Grand Cherokee fuel pump not come on when it is cold but activates when it gets warm?
The engine control module, ECM controls the fuel pump. The ECM grounds the ASD relay, the injectors, the coil and the fuel pump relay. For the engine control module to ground, these components need to see the engine rotate by the crank sensor. If you have never replaced the ASD relay, you will have to replace it now. If you have replaced it then you need to check for spark when the engine does not start. If you have spark then you know that the crank sensor is good. If there is no spark then you will have to replace the crank sensor as the ECM may cause problems with its drivers when it is cold.
I replaced the fuel pump, spark plug and pump relay but my 1998 Grand Cherokee is still not starting. How do I resolve this issue?
You need to check you battery voltage at the fuel pump relay socket. You should be getting at least 12v. You need to remove the fuel pump relay and check for + 12v at the cav. #16 with a test light connected to the ground. If you have power at this terminal, see if the fuel pump works. If you are not getting any spark it indicates a faulty crankshaft position sensor. When the PCM does not receive signals from the crankshaft position sensor it turns the auto shut down relay off and does not fire the ignition coil. You need to check the PCM with a scan tool to check if the crankshaft receives a signal when you crank the engine. If the crankshaft position sensor is bad you will need to replace it. Use an original Mopar part.
Periodic fuel pump inspection is important, as identifying early signs of wear and tear can prevent major problems with the fuel pump later on. For tips on installing a quality Jeep fuel pump or replacing Jeep fuel pump parts you should speak to an Expert.