capnzzz

Hello, I have been trying to diagnose a fuel pump issue with my 91 stang. No fuel pump priming is hear when key on. There is power input to the inertia switch (thus eliminating all relays, ecm, wiring to the pump as a problem). There is no output from the inertia switch. I bypassed the switch and the voltage went from 12v to 0v as soon as I jumped the two wires. I went ahead and replaced the fuel pump...still same issue. Any one have any ideas??

capnzzz

Update..checked fuel pump relay under seat..it is clicking when key on..battery power to red lead (from ignition) and constant power from pink lead..switched power from relay is turning test light on for a couple of seconds then off. When hooking up light to constant and the other lead to ground wire (blue/orange) llight lights up...then goes off indicating a good ground from ecm. So it looks like the fuel pump relay is working as it should and all the tests check out there. Still stumped??

mattdel

I'm having trouble following your diag procedure, but just an FYI: test lights aren't capable of testing grounds. You need a DVOM hooked in series.

ttocs

all fuses ok?

capnzzz

I think I found the issue..at fuel pump relay showing full voltage on key on and constant wires. relay is clicking allowing signal to go through to pump..but the pump will only run when relay is jumped between the constant and key on terminals..must have burnt up some contacts in there with the old failing pump. About to swap the relay out so hopefully this is it.