Fuel Pump Runs Continuously 1990 F150 4.9L

ai2a

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Panic set in when the fault occurred - but the repair was fairly simple (I think I have it cured). After recharging the battery (yeah it ran the battery dead before I started the repair), I got a code puller and grabbed the EEC test connector. This immediately stopped the running fuel pump. There is a small fuel pump relay that sets inline with a connector on the bottom of what I suspect is the EEC module. After starting and then stopping the engine, the problem returned. I lightly tapped the module with my finger and the problem again disappeared. I went ahead and pulled the touble codes. One code indicated a secondary fuel pump wiring fault and an EEC ROM Code error.

Just for giggles, I replaced the fuel pump relay and cleaned the contacts on the connectors attached below the EEC module. This also eliminated an error code 15 (ROM CODE error in EEC). Before doing this, I do suggest that folks disconnect a battery terminal to avoid damaging the EEC.

I was lucky in that this vehicle has never seen any real use in its 18 year life. It has less than 54k actual miles and has never been modified in any way. I hope that this experience might help others who encounter a similar problem.

Best Regards,
David Clark
 

Transman

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It does help to be lucky! This kind of problem can be a major nightmare for anyone, not just professionals. Getting lucky and having it act out and tapping to make it work again is a blessing in any mans life, Sorry Con! or Woman's life. I had a car that everyone in the shop had been on that nobody could find the problem. I discovered that I could make it happen by power braking a little, The only way to make it act out was on the highway gentle cruise. From there I looked at what moved when the engine did and discovered the ground wire that went from body to engine. When I gently wiggled it the engine would flutter. The problem was the ground wire was broken inside the insulation, looked perfect outside but when the engine moved the contact would break a bit causing a loss of power. I was lucky but looked like a master tech and in my glory. As a general rule... I will take luck any day.
Thanks for posting what you found, Transman
 
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