Inertia switch

92SHO37 · Jun 24, 2007

I have a 94 cobra, and after it runs for awhile, and I shut the car off, when I turn the key back over to on, the fuel pump just keeps turning on and off on and off, would this an inertia switch, fuel pump relay, or any ideas? Thanks in advance.

HISSIN50 · Jun 24, 2007

How long does the on/off cycling occur? Is it indefinitely or does the pump shut off and stay off within 5 seconds?

92SHO37 · Jun 24, 2007

when the car is cold, I turn the key on, pump kicks in for 2 seconds, shuts off for 2-3 seconds, then back off again, and I can start it, not a really big deal. When the car is warm, same thing but the pump just repeats the cycle on off on off, and I can manage to get the car started, that's how it runs, (keeping rpms up) runs tries to quit rpms drop, picks back up, then tries to quit again, about every 5 seconds.

HISSIN50 · Jun 24, 2007

Check for codes.

Because of the cyclic nature of the priming, it is likely NOT the inertia switch, FP relay (itself), etc. It could be a puter issue (sending a ground pulse to the FP relay repeatedly), a bad ignition switch connection (the puter keeps thinking you're turning the key on), etc. You should be spitting a primary or secondary fuel circuit code with this issue. That could help narrow it down.

The underlying theory: when you turn the key on, the pump primes for 2-5 seconds. It remains off until the PIP circuit is active, at which time the pump runs non-stop.

92SHO37 · Jun 24, 2007

I scanned for codes, KOEO a 111 came up(system pass) KOER 172 came up(left bank lean) That's all I got. I will check out the ignition switch. The car goes back to normal after it cool down a little, but thanks for the replys so far, helps out alot.

mo_dingo · Jun 26, 2007

HISSIN50 said:
Check for codes.

Because of the cyclic nature of the priming, it is likely NOT the inertia switch, FP relay (itself), etc. It could be a puter issue (sending a ground pulse to the FP relay repeatedly), a bad ignition switch connection (the puter keeps thinking you're turning the key on), etc. You should be spitting a primary or secondary fuel circuit code with this issue. That could help narrow it down.

The underlying theory: when you turn the key on, the pump primes for 2-5 seconds. It remains off until the PIP circuit is active, at which time the pump runs non-stop.

PIP's are known for their heat problems after time. After you ensure your ignition is ok, you might want to look there next. Good luck.

Could this be a ignition module problem also JT?

HISSIN50 · Jun 26, 2007

mo_dingo said:
Could this be a ignition module problem also JT?

Scott, with the way the engine is running for him, it very well could be. Earlier I couldnt interpret the part about the car's idle also ebbing and flowing (I was focusing only on the fuel pump priming).

SHO, when you are getting ready to drive the car, I'd ground the FP control terminal at the self test connector (this is the same wire which is grounded via the computer. The purpose of this terminal is to allow you go have the pump constantly run while doing diagnostics). Now let the car run and see if this BS goes away. This would help isolate if the issue is the ground-pathway in the computer itself (the ground straps have failed before, but normally it's all or nada).

An alternative is to get a FP gauge on there. If you're losing and gaining power output to the pump, your pressure should be all over the place.

Lastly, if you have a means of viewing PIDs (live engine parameters), this can be quite helpful (dont go buy anything but if you have a buddy with a scanner, it could be worth tossing on).

Good luck.

92SHO37 · Jul 5, 2007

The problem with my car was the old not soo good Jetchip that was in it, I pulled it out, car runs/starts better than when I bought the car, chip was in car when I bought it. I will probably get a Diablo chip now. Thanks for the reply's HISSIN50 and mo_dingo.

HISSIN50 · Jul 5, 2007

Nice work getting it fixed. I can honestly say that I've never seen a chip cause a FP run-on issue and never would have been able to help you figure that out.

Nice work!

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