Electric fuel pump diagnosis Houston, we have a problem Part one of two By Mike Mavrigian
A
ll too often when a no-start condition or hard-start is encountered, some techs may be too quick to automatically blame the electric fuel pump. If you talk to any rebuilder/remanufacturer or new parts manufacturer’s warranty folks, they’ll tell you that in the majority of return cases, the fuel pump that was returned as faulty was in fact problem-free. Before you jump the gun and swap out a fuel pump, consider performing a simple voltage drop test to check the circuits that are responsible for pump activation.
Do we have fuel? We realize how basic this sounds, but before performing any type of diagnosis
related to a suspected fuel pump problem, verify that there’s fuel in the vehicle tank. Whether you’re dealing with a gas or diesel engine, she’s not going to fre unless the pump has available fuel to suck out of the tank and push forward to the injectors. You may laugh at this reminder, but if we didn’t mention this, I’m sure we’d get letters criticizing us for not including this caution. Electric fuel pumps on electronically controlled fuel injection systems need to produce enough “high” pressure to allow the injectors to produce a suffcient spray of atomized fuel into the intake path (or into the combustion chamber in a directinjection system). Fuel pressure is typically in the 35 to 45 psi range. The electric fuel pump needs to be able to produce more pressure and fow than is needed, with pressure being controlled within the engine’s requirement range by the pressure
A non-delivery or weak delivery fuel problem shouldn’t automatically be blamed on the fuel pump. In far too many instances, fuel pumps are replaced needlessly.
36 | March/April 2013
