Fuel pump relay not getting signal from computer

JavaG66 · Jun 5, 2010

Hi,
The computer on my 86 ranger is not sending a signal to the fuel pump relay. I disconnected the computer and grounded the wire that runs to the relay; the relay clicks in fine and passes current on to the inertia switch. Is there any condition that would cause this other than a bad computer?

Thanks so much!
Hal

disciplerocks · Jun 5, 2010

Can you jump the fuel pump and it turns on? If so its probably the computer. My dad just had this problem while working on my brothers car. Just pick one up from the junkyard. They are only like 12 bucks here.

JavaG66 · Jun 5, 2010

The fuel pump runs when the wire that would otherwise hook into the computer is grounded. Only $12?

disciplerocks · Jun 5, 2010

From the junkyard yes. From auto parts store it would be closer to 100 or so probably.

kimcrwbr1 · Jun 5, 2010

trace the wire to the computer first to see if you have continuity could be a loose or corroded connector or break in the wire.

JavaG66 · Jun 5, 2010

I was grounding the circuit about 2" from the computer's connector (disconnected).

BRUTUS_T_HOG · Jun 6, 2010

well that depends. is the computer grounding the fuel injectors?

i've dealt with this same issue quite a few times.. mostly it was a bad computer.. but occasionally it was a bad ECM power supply or ground.

JavaG66 · Jun 6, 2010

The computer is getting power at all the right places. I don't know if the injectors are being grounded; I will inspect the grounds and get back to you. Thanks again for all your suggestions, they really help.
-Hal

JavaG66 · Jun 6, 2010

The truck is running again. :icon_confused:

Here is what I did.
1)While the computer was out, I peeked inside to see if there were any 'user serviceable parts' or bad solder joints. None noted of either.
2)My battery ground cable has 3 wires, a large one to the engine, a medium sized one to the body, and a third one to harness-land via a pull-apart connector. Even though the body ground looked ok, I took it apart and shined it up and re-assembled it with some bulb grease. I verified that there was continuity through the pull apart connector on the small wire.
3) I reinstalled the computer. The screw that holds the computer snugly in its bracket was slightly corroded. I cleaned it up and the small ground lug that goes under it and put it all back together. I snugged up the 60 pin connector.
4) Insert key, hear fuel pump and crank engine; engine fires right off and runs as normal.

So now I am wondering when this problem will re-appear, and what happened that caused it to go away. Overall, this has been a dependable truck, but, like me, I guess old age is setting in.

BRUTUS_T_HOG · Jun 6, 2010

told you. bad ground/connection.

more often its just a bad ECM though

disciplerocks · Jun 6, 2010

Well cool. Glad you got her running. I would add another ground wire or two off your battery. You can never have enough.

cheerleader2012 · Jun 10, 2010

I've got the same problem with my '88 ranger. jumping the relay can get the pump to run but won't start. I was thinking computer but I'll start with grounds and keep my fingers crossed. Hope I can find a $12 computer

Fuel pump relay not getting signal from computer

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