90 F150 Fuel Problem

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Apr 16, 2009 | 07:25 PM

FlyTSI

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90 F150 Fuel Problem

I have a 90 F150 with a 5.0 . The other day I was driving it and it just died. The front tank never has worked so I was running off the back one. I installed a new fuel pump and it wont fire up unless I jump the wire at the relay, and when I do that the pump sounds weak. I looked on the truck to see if it has the high pressure pump on the frame and I didnt see one. I did notice that it appears that I only have 6 volts at the wire that plugs into the sender. Could it be the relay, im very confused.
Thanks in advance.
Kenny

Apr 16, 2009 | 09:23 PM

subford

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From: Easton,Ks

What wire are you jumping at the relay?
Does it run OK when you jump this wire?
Do worry about the sender it has nothing to do with it not running unless you have lost the ground at the radiator support.

Apr 17, 2009 | 05:40 AM

FlyTSI

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I am jumping the wire that the relay would normaly kick in from the yellow wire, I think its blue and yellow, its dark outside atm so I cant tell exactly. It does not run when jumped , the fuel pump does kick in but it sounds weak and I dont get any pressure. The fuel pump wont kick at all with the relay hooked up and the jumper wire dissconnected. Could it be something with a ground to the radiator ?? The sender on the back tank works.
Thanks
Kenny

Apr 17, 2009 | 06:59 AM

subford

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From: Easton,Ks

If you are grounding the Blue wire with a Yellow stripe and your fuel pump runs weak then yes you have a bad ground at the radiator. That wire runs from your fuel gauge selector switch to the fuel sender (see attached diagram) and with no ground it could back feed and run the pump with less then normal power.

Try grounding Pin#6 of the self-test (DLC/VIP) connector (see diagram attached) with the key on and see if the selected pump runs.

1990 Fuel system wiring:
http://i54.photobucket.com/albums/g9...el1990F150.jpg

Self-Test Connector:
http://i54.photobucket.com/albums/g9...taLinkConn.jpg

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Apr 17, 2009 | 05:16 PM

FlyTSI

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Thanks everyone for their help thus far. I replaced the relay today and the fuel pump now has 12 volts and runs. The problem I am having now is I only get 20psi of pressure, it idles ok but falls on its face when your driving it. Any further ideas on this.
Thanks so far, u guys are great.
Have a great weekend
Kenny

Apr 20, 2009 | 04:16 PM

FlyTSI

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I still haven't been able to figure out why I am only getting 20 psi fuel pressure. I unhooked the regulator and it made no difference what so ever. Any ideas ???
Thanks again.