1990 Mustang Computer Problem? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 6 Old 06-03-2011, 08:08 AM Thread Starter
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1990 Mustang Computer Problem?

I have a 90 saleen mustang...I have a feeling the computer may be bad. When you turn the key in the on position (the EEC relay and fuel pump relay stay energized...) The fuel pump does not shut off if the key is turned in the on position...it should shut off after 2-3 seconds I believe...We have triend changing out computers with a used one...however we still have the same problem (2nd computer could be bad). My friend thats helping me work on the car said this is a pretty common problem with Fords in general. Are there any other problems that could be causing this? Also the car will not start in the morning without spraying start fluid (or something similar) directly into the intake...Any suggestions? Thanks all!

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post #2 of 6 Old 06-05-2011, 04:58 PM
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I had a similar problem, it turned out to be a bad/flaky fuel pump relay.

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post #3 of 6 Old 06-15-2011, 04:19 PM Thread Starter
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Thanks for the heads up...I've tried 2 dif computers and no luck...guess its time to change fuel pump relay...thanks!

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post #4 of 6 Old 06-16-2011, 03:38 PM
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The computer provides the ground to the coil of the relay. Some people will sometimes re-wire them so that it goes straight to ground. This will cause what you're experiencing.

Another possibility is that the insulation on that wire between the computer and the relay has worn somewhere shorting to ground.

The ground wire for the fuel pump relay coil is Tan/lt.green. It should NOT be grounded with the key off, check it.


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post #5 of 6 Old 06-22-2011, 08:04 PM
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The fuel pump staying on problem was almost always a bad relay they are cheap enough to guess with , the hard starting your talking about is probably the fuel pressure bleeding down over night which could be a bad injector that leaks down, a fuel leak or the check valve in the pump it should hold at least a little pressure so when it starts cold it doesnt have to crank a long time thats why you have the prime for 2-3 seconds when you turn the key on to pressure it up but if the lines drain all the fuel out it will start hard. test that with a fuel guage. as a general rule though I worked at a Ford dealer for many years during the 80s and 90s and 90% of Ford computers that were replaced were not bad so that is almost always NOT the problem , Im not saying they never are bad but compared to GMs of the same era ECC IV pcms are bullet proof. I cant off hand think of a good way to test for the fuel leak without special tools or crimping fuel lines though. Hope this helps you out.
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post #6 of 6 Old 07-07-2011, 10:45 PM Thread Starter
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Guys...thank you for all of your help...Here's the current gremlin I'm dealing with...Swapped out the computer that was in my car (we believe it had been either programmed or tampered with) and replaced with used unit...The new computer caused the fuel pump to shut off as it should...however the car idled all over the place...after a few days the car now idles better but the fuel pump now doesnt shut off with key in on position like it did after we first installed the computer...Now the other weird thing...My car is getting maybe 2 miles per gallong (maybe)...it stinks of gasoline and if you hang out in the garage your eyes hurt...there are no signs of leaks near the injectors or near the gas tank...Any idea what could cause this? The good right now...car starts in the morning after sitting (wouldnt do that before)...the bad...2 miles per gallon (maybe)...What would make a mustang dump fuel to this extent? Any ideas? This car has been modded but to what extent internally I do not know...sounds like it may have a b cam or something similar...however the valve covers look they've never been off the car...Do you think its a faulty injector (spraying wide open all the time)...vacuum leak of some sort...etc? Thanks everyone for the help!!!

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