1991 F-150 5.8 auto.
the problem i have is that while running or idle at times the fuel pump relay starts to chatter then the engine stops. there are no diagnostics codes that show up. i have replaced the relay and it did not solve the problem. this problem is intermittent. i can turn on the ignition and it will chatter then i can turn the ignition off then on and the chatter stops allowing the engine to start. i searched other posts and someone stated that it was probably a bad ground connection. does someone have a diagram of the fuel relay circuit so that i can try to locate where the ground problem may be. perhaps someone had this problem and can tell me how to fix it. i sure would appreciate any help. thanks, john

 

The turn on lead on the fuel pump relay is grounded through the engine computer (it commands the relay when to energize). There is a wire on the diagnostic port that you can ground to energize the relay. I would try grounding that wire and see if the relay still chatters.

 

i don't know which pin to ground, could you be more specific. thanks

 

Here you go . Just jump the fuel pump wire to ground.

 

thanks for the diagram. i did ground the pin and it did stop the chatter however i could hear a faint clicking noise that seems to be coming from the rear of the engine or behind the firewall. by grounding the pin does this verify that the EEC is bad or what needs to be done. thanks, john

 

i want to thank you for the inputs on my problem. i replaced the computer and as of now running good.

 

Glad you got it fixed