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Fuel Pump Issues/ Looking for a 91 fuel pump wiring diagram

ThatGuyInGreen

New Member
Joined
Nov 20, 2022
Messages
2
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Location
Denver, USA
Vehicle Year
1991
Make / Model
Ford Ranger 4.0
Transmission
Manual
Hey all! So my truck (1991 4.0 XLT 5 speed manual) was reliable when it was warmer out, it would start up every time just fine. as it got colder, around 30 degrees the fuel pump would prime intermittently, sometimes it would prime sometimes it wouldn't, and I'd have a crank, no start. I confirmed the truck has spark, as the truck would run for 1-2 seconds with a good shot of starting fluid. was told by mechanic buddies that that's usually a sign of a failing fuel pump. It got colder, and then no priming whatsoever from the fuel pump, warm or cold outside. Replaced the entire pump assembly, no prime. Pulled 3 different fuel pump relays and 2 ecu relays from some 91's at my local u-pull; swapped them all in turns, no prime. The relays do make an audible click so I don't think they're bad, will probably learn to test them properly this weekend with a good ol' youtube education session to tell for sure. Checked the 30A fuse and swapped for good measure. No Prime. checked the inertia switch; I popped it up and tired to start no relay click, popped back down and heard the click again. no Prime. At this point, I'm going to test the sending unit plug and follow the power with a power probe but am having a hell of a hard time trying to find a proper wiring diagram for the fuel pump circuit that is detailed enough for me to properly troubleshoot. does anyone have a link to a diagram or a screenshot for a fuel pump system on a 91 4.0? any tips/advise? im trying to turn this ol' shitbox with gorgeous bones back into a really nice reliable daily driver. Thanks! :)
 


franklin2

Well-Known Member
Joined
Dec 24, 2019
Messages
2,361
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Location
Virginia
Vehicle Year
1984
Make / Model
Bronco II
Transmission
Manual
Here's a diagram.
 

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