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Diagnosing Fuel Pump Problems

Gas tank

When issues of starting, rough idle, or misfire come up, one of the prime culprits is often the fuel pump. Pumps are expensive and time-consuming to replace, however, so testing before buying and installing new parts is a must. Not knowing what the problem is and blindly throwing parts at it until it's resolved (or you're broke) are not a smart way to diagnose and fix things.

The first thing to do is to do a basic fuel pressure test. Once that is complete, a fuel pressure and volume test should be done. These tests should definitively tell you whether the fuel pump is malfunctioning. They will at least tell you if fuel is reaching the fuel rail (and injectors) at the proper pressure and volume.

If you have proper fuel volume and pressure, your issue is almost assuredly not the pump, but may instead be electrial. Probably the connections to the injectors themselves.

If your testing does show fault with the pump and if you've ruled out relay or circuit issues to the pump itself, you'll need to remove it to do further testing on its circuits and on the pump itself. This will likely involve dropping or removing the gas tank. Before doing so, be sure you've also checked the voltage and its consistency for the fuel pump's power supply. Faults in this circuit could be the real problem.

Most of the time that a fuel pump has problems operating, the solution is to just replace it. Diagnostics and repair can be done on a pump, but this is usually well beyond the scope of a do-it-yourself mechanic's repertoire. Even most professionals will replace rather than tinker. It can pay to do basic circuit and continuity tests on the pump's internal electronics once it's removed from the fuel tank. Sometimes, a ground wire or other small problem may be the real culprit, which can save having to purchase a new pump.