My 88 Iroc 305 TPI has problems starting. It cranks for a while then starts. Sometimes shorter, sometimes longer. Can't find any common ground with the occurances. So I took it to shop for a fuel pressure check. They said when you first start cranking you get around 10 PSI and then when the car starts you have 40 PSI. Then he said i wasn't getting enough voltage to the pump and that there was a code 54. The car always starts just it takes a little while. So i figured, what's 15 bucks and bought a new fuel pump relay. Didn't fix the problem. The pump sometimes stays on for a long time after the car is off. Sometimes hours after. havn't checked for this since the new relay. My dad thinks it may be a faulty ecm. I hope not. Anyone had this problem? Any ideas on how the diagnose it?

 

There are two power supplies for the fuel pump. One is through the relay, the other is through the auxilliary oil pressure switch. If either is sticking, the pump will run on after shut down. A few seconds of run-on is normal as oil pressure bleeds down, but that should last no longer than 5-10 seconds.

The easiest way to isolate the cause is to unplug the FP relay while the pump is running. If the pump stops, the relay is either sticking or the ECM or wiring is energizing the relay when it should be off. If the pump still runs after the relay is disconnected, the probable cause is a sticking oil pressure switch.