I have a 1990 F150 XLT Lariat with A/T and 5.0 The front tank quit working on me a couple years ago so I have only been using the rear tank. Truck ran fine yesterday, when I went out to start this morning would not start. Truck cranks so battery, altenator and starter good. I did notice I don't hear the fuel pump prime as I normally do. I do hear the relay under the hood click, where should I start from here, could the relay be bad even though it is clicking or anyting else I could check that may not be the fuel pump. Once again this truck has the duel tanks and the front tank has not been working for years. Thanks for any help or suggestions.

 

relay could still be bad, take the relay out and make a jumper wire, put it in the contacts the relay NO is, look if it runs then, there's also somewhere a test connection that can be made at the EEC-self test connector (forgot how)
does the pump in the tank run? checked fuses?

 

have you checked the pressure? the pump may be priming running, but not priming to the pressure needed. Had this issue on our 1990 f250. pump ran, but wasn't pumping the correct pressure that was needed to keep the truck running.

 

Just so you know, the 1990 models no longer have the in frame pump. They started putting a high pressure pump in the tank(s) and done away with the in frame pump. 1990 was the first year for this. I just thought I would point that out.

 

Fo sho, can, and they are known to do that. You could be hearing the EEC relay anyway.

You need first 12v on the yellow power input to the fuel pump relay, and then 12 on the dark green/yellow wire after the key is cycled. This is only a few seconds if the engine doesn't fire.

Additionally, you can manually ground the fuel pump relay causing it to trip and run the fuel pump with the light blue/orange wire on the OBD1 port making it easy to shoot for power the rest of the circuit.

Next power runs to the inertia switch under the dash near the brake master cylinder, so check for 12v there.

Now, pull the dash switch and input is red/yellow. Front tank output is the red wire, and rear tank output when selected is brown with white.

Adrianspeeder

 

tanks for pointing it out, was thinking from my 88 wich still has the inline high pressure pump