Hey guys,
Ive been havin a helluva time diagnosing why my fuel pump on my 97 F-250 HD gas will not work. The truck came with two tanks, but I eliminated the front tank 3 years ago (rotted and leaking), and replaced the rear tank/pump at the same time. Started by assuming, on bad advice, to replace the rear fuel pump yesterday.

Well, long story short, it still doesnt work. I then replaced the relay, but am still just getting a click instead of a humm, when cycling the key. Ive double checked the inertial switch on the passenger side kick panel, and thats depressed.

Any ideas on where to go from here and how to properly test the relay box and fuel pump harness?

Any thoughts are greatly appreciated
REW

 

As I told you in the other thread:
First of all I take it you have an OBD-I EEC-IV system.
If so just ground pin #6 of the self-test plug, turn on the key and see if the fuel pumps run.
If they do not then go to the inertial switch on the passenger side kick panel and check for voltage with a load type test light. A volt meter will not work here as it will say there is voltage when there is not.

If the fuel pump do run when you ground pin #6 of the self-test plug and turn on the key you may have a bad PCM Computer. But short pin #2 to pin #6 of the of the self-test plug, turn on the key and see if the fuel pumps still run.
If they do not then you have a ground problem coming from the body ground to pin #40 & #60 of the PCM Computer.

 

awesome, thank you. and yes, it is OBD-I

 

so I just got done testing the self-test plug with a jumper wire grounded, using a test light. When I turned the key, the fuel pump did not engage, and I checked the fuel rail and no pressure developed. The test light did light. (I only used this method as it was easy to use the alligator clips on the jumper and the needle held nicely in the hood springs).

after that, I went to your second step, the inertial switch. after unclipping the plug, and testing with the test lamp, I had voltage there, (green wire i think)

after this i decided to test the pump harness back at the tank, while my wife turned the key, with the test lamp. After three tries, I determined there was no voltage at all in any of the four wires. (this I did after reattaching the inertial switch plug ).

I did hear a second click coming from the rear of the truck while completeing this last test. Got me wondering about the wires in the rear of the truck, such as the trailer lights and tail lights. Seems like a bad ground or arc somewhere in the system...no?

As always , thanks ahead for any ideas

 

If you have power at the inertial switch and none at the tank then I would say you have a bad fuel tank selector switch in the dash or the plug is off the back of the switch.

 

Thank you for that last suggestion! I hadn't even looked at that switch, and havn't used it in three years, since I took the front tank out. It had been flipped, probably when i went to turn off the hazard lights, by accident. That was it all along. I'm gonna tape that bugger down.

Thanks so much for your advice and thoughts. Absolutely priceless

REW