I have 1990 F150 4.9L, a few days ago I noticed that when I turn the key foward the fuel pump stays running all the time without even trying to start the truck, I know that it should come on for a couple of seconds then cutoff, but this one just started doing that and I cant seem to keep the truck running, it cuts off and the check engine light comes on, I,ve already tried changing the fuel pumps relay with a used one, still does the same thing. Can someone tell me if there is another thing I should be checking, has two fuel tanks and both of them work. Thanks.

 

is anything wrong with the fuel pump wiring? thats a sign of a bad computer.

 

Not that I know of, but I'll check on that, I tried again today and after several attempts it worked fine for a while, took it for a spin no problems then I got home tried it several times no problem, several hours later when I tried to start it the problem started again.

 

This isn't a fuel delivery problem. It's an electrical problem with the FP relay (not likely) or an electronic problem inside the EEC (I've noticed this exact symptom appearing more & more frequently on all the pre-'97 BBSs). When the pump stays running, pull the relay out of its socket & test the ground trigger. If it's actually grounded, disconnect the EEC (try not to disturb the wiring harness) & test that circuit for short to ground. If it's not, replace the EEC.

This caption & the NEXT few describe those relays & their pinouts.



Once you fix this symptom, do the procedure described in those pics.

 

How do I test the ground trigger? Sorry for the ignorance, my knowledge of vehicles is basic. And where is the EEC located? Thanks.

 

This isn't really something to learn on - better to pay a pro this time & start learning on the easier & cheaper projects.

The EEC is in the driver's kick panel, beside the e-brake mechanism.