My '85 F150 is giving me a severe headache! I keep getting getting a reading for code 87 - primary fuel pump circuit failure. The truck is driveable, but it stalls when I step on the accelerator. I have replaced the external fuel pump, fuel filter, oxygen sensor, coolant temperature sensor,and fuel pump relay. I have observed two things upon switching the ignition to the "RUN" position: a relay under the dash makes a clicking sound and the external fuel pump takes a while to receive fuel. I'm not sure whether it's the internal fuel pumps or the wiring. My truck has dual tanks by the way. Any help will be appreciated.

 

Here is a factory wiring diagram that might be of some help. It says it's for a 1985, but I dont see any external pump listed in it.

I suggest looking for and checking each component in turn from the fuse panel, to the starter solenoid, to the pumps, checking for continuity, checking the grounds, and checking for intermittant faults in power supply from each component seperately.

Hope this helps.

http://i447.photobucket.com/albums/q...l/scan0003.jpg