Engine cranks but will not turn over

JOE LAHEY

MEMBER
2004 FORD MUSTANG
3.9L
V6
AUTOMATIC
128,000 MILES

My car cranks but won't turn over. I thought it might be the fuel pump. I replaced the fuel filter and was about to replace the pump too, but the car was able to start after the filter was replaced. I turned the car off and tried starting it a second time, but again it would crank but not turn over. Since it started I decided not to replace the fuel pump because the engine was receiving fuel and I didn't want to waste money replacing that. I then replaced all the spark plugs because they were very old and very worn down. It was able to start again, but when I tried to start it a second time it kept cranking and not turning over. The battery and alternator are fairly new and I'm reading 12.2-12.3 volts from the battery. It seems like the car is able to start if it is left alone for awhile but then will not start directly after that. What should I check next?

1 Reply

BMDOUBLE

MECHANIC
1,139 POSTS

I've attached an illustrated diagram of a basic test that I always start with for verifying power at the inertia switch and also a wire-jumper test to verify if your issue is with the fuel pump driver module as well as the module location. If you're not getting power to the inertia switch with the key on (momentary 12 volt signal), we could be looking at an issue with the constant control relay module mounted behind the passenger side fender, but begin here and let us know what you find.

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