5.0L (1979-1995) Mustang Technical discussions on 5.0 Liter Mustangs within. This does not include the 5.0 from the 2011 Mustang GT. That information is in the 2005-1011 section.

89 5.0 electrical problem.

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Old 07-23-2010, 08:03 PM
  #1  
Justinr1001
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Default 89 5.0 electrical problem.

I just bought an 89 lx 5.0 and it has a few problems. First off the fuel pump is hot wired to the battery with a toggle switch in the console. The guy thought the pump went out, replaced it and it still didn't work so he did that. He "said" it ran after that for a while and was then parked for 2-3 months. I checked the old pump along with the new one and all is good there, and he said he replaced the relay for it under the seat. What would make it not come on with the key to begin with? Secondly, when i bought it, it wouldn't start. I replaced the relay that is above the computer, stuck wires from the pump straight to a battery and it started, but it doesn't start when its cranking. When i let off the key is when it hits. Its like it isn't getting fire when its cranking. It is a converted 4cyl, but it was done a long time ago and everything looks factory under the hood. It idles and revs just fine. Anybody got any ideas?

Sorry for the long jumbled post, lol just trying to get everything in there. Mucho thanks.
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Old 07-23-2010, 10:11 PM
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65Raven65
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Originally Posted by Justinr1001
but it doesn't start when its cranking. When i let off the key is when it hits.


Its been a few years since I had my '89, but I think thats how its supposed to be. In other words, if you turn the key to the ignition without starting it, you'll hear the fuel pump buzz for a second then cut off. Then, when you crank the motor, the fuel pump will kick back on and stay on.

Sounds right to me, but its been almost a decade. Or maybe Im misunderstanding the question.
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Old 07-23-2010, 11:36 PM
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aode08
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no ground to the Fuel Pump relay

Bad Fuel Pump Inertia Switch , in the back of the car inside driver side I think, its been a while, if someone hits you, it turn off the fuel pump.

In the 90's it was a prank to smack the quarter panel of a Ford and the swith would open, the car would not start.
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