Fuel system shutting down

Swamp Donkey · Jan 26, 2012

Please help! Twice in the past week the fuel system been inop when I got in the truck. (It is an 86 B2). I turn the key and the fuel pump won't run, and it just cranks but won't turn over. I was messing around with the Chilton's manual and discovered if I trip the fuel inertia switch, crank it for 20 seconds, and then reset the switch it starts right up. Any ideas would be much appreciated, I'm trying to teach myself on the truck!

Earl43P · Jan 26, 2012

Those two wires going to the inertia switch connector? Splice them together with a Scotchlock. If that fixes it, relace the inertia switch and remove the Scotchlock.

My $$ is on a bad fuel pump relay however.

Another thing to consider is the PCM relay. If IT isn't working, neither will the fuel pump relay. Most vehicles, if the PCM relay is working, the Check Engine Light comes on when the Key is turned to Run. If that isn't happening, replace the PCM relay.

See here: http://www.therangerstation.com/tech_library/EDiagrams/files/Diagrams_ElectronciEngControls2_9_1of3.JPG

Swamp Donkey · Jan 27, 2012

Thanks for the info, much appreciated. I'll give all this a shot and see what happens.

big red 138 · Jan 27, 2012

id say just bypass the inertia switch all together. they seem to cause alot of problems. every B2 owner i know has had issues with it, including me. i just cut the wires and soldered them together, bypassing it all together. did it about a year ago. disregarding the knowledge of the inertia switch bieng a common problem, the relay is a good thing to check, anytime your trying to diagnose a problem, and theres a relay in the circuit, start there.

lastly, check the wiring from the relay to the firewall, my step dads 89 B2 had some gremlin that fried the fuel pump wiring between the relay and the firewall, to include the OBD connector, and it never hurts to check the wiring on a 20 something year old truck

Nathan123 · Jan 27, 2012

If you jump the inertia switch with no luck, check you codes. This happened to me and I got a code (I dont remember what it was but the book tells you) about a open ground in PCM for the fuel pump circuit. If your fuel pump relay is workin fine, try grounding the fuel pump. It seemed to me the pump relay has to turn on the hot and the computer turns on the ground. If your out of options, it might help.

big red 138 · Jan 27, 2012

Nathan123 said:
If you jump the inertia switch with no luck, check you codes. This happened to me and I got a code (I dont remember what it was but the book tells you) about a open ground in PCM for the fuel pump circuit. If your fuel pump relay is workin fine, try grounding the fuel pump. It seemed to me the pump relay has to turn on the hot and the computer turns on the ground. If your out of options, it might help.

the computer sends the signal to the relay to go hot.... ignition (run)->pcm->fuel pump relay. the pcm does however monitor circuit continuity ( in theory). ive got the wiring diagram somewhere, ill try to get it up here tommarow.

how did you solve the problem of that code? i think when i rewired my fuel system there was a 5v reference wire from the pcm, was that your problem?

Nathan123 · Jan 27, 2012

I replaced the fuel pump and spliced in a direct ground. That 5 volts sounds about right though, I never measured anything I just remember reading about it. When I was sitting in the parking lot with a bronco that wouldnt start, the check engine light wasnt on, I just pulled the codes and got 95. I jut looked it up, my haynes book says "Fuel pump circuit open- EEC processor to motor ground" I just looked at the diagram and figured the computer closes the ground and that the fuel pump relay could do it by itself. I never checked codes after, who knows I may still have it.

Swamp Donkey · Feb 26, 2012

Work took me away for a few weeks, but finally got a chance to work on it. Pulled the inertial fuel switch off and found a short where the wires plug in to the switch. I removed the switch and the plug and spliced the wires together, and the truck runs great again. I'm going to order a new pump and connector from the dealer, but I'll just drive it with the splice until they come in. Thanks for the help and ideas on this.

Fuel system shutting down

Swamp Donkey

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Earl43P

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big red 138

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