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1990 K1500 fuel relay work around

W

wsmm

Member
I think I have a bad fuel relay according to the test procedure. If I put power to the adl fuel pump test port the pump runs. I plan on picking one up tomorrow and installing it, couldn't get to the store in time today. I called and they're holding one for me. My real question though is is there a way to wire around and bypass the relay and have the fuel pump run so that you can use the truck. If so how could you do it. I would like to know so that I could wire up a backup system in place in case this happens again when I need to plow.
Thanks for your help,
Bill
 
Some years ago I made up a test harness from a cord that plugs into the cigarette lighter, a 15 Amp fuse in a holder, and a narrow strip of brass that slides into the appropriate ALDL connector "slot". It hangs on my tool cart, and I've used it a few times since,

No reason you couldn't rig one up (if you haven't already for testing), leave it plugged in, and drive to the parts store for your new relay. Or plow snow with it all day.

'Course, it defeats the "nanny" "fuel pump shuts off with the engine" feature.
 
Thank you very much. I was thinking of doing something like that and just needed conformation that it would work and be okay to do. I currently have a test unit with a 25A circuit breaker that I could use by just making an extension. Just got done testing my fuel pump relay off of the truck using a multi-meter and a 9 volt battery. It works fine, so I think I have a problem in the wiring or some other sensor or switch. I tested the fuel pump connector with the key on and the key off with a power probe and got the following results,
Key Off socket A 12 v pos Socket C open, Socket F open, socket E ground, socket D Ground.
Key ON socket A 12 v pos, socket C open, socket F, E, D ground

socket diagram __ ____ __

F E D

___ ___

A C

Need to try and make some more sense out of the wiring diagram. Liked the older wiring diagrams better.
 
The fuel pump should run while cranking,then the oil pressure switch closes and energizes the relay.there should be 2 oil pressure switches,one for the gauge and one for the fuel pump relay IIRC
 
Fuelpump relay is s.p.d.t., powering fuelpump from ALDL only works if fuelpump relay is NOT in "pulled in" as it normally is when the engine is running.

Computer powers relay coil through "F" for a few seconds when key is switched "ON", then continuously while engine is cranking or running.

If engine is cranked long enough to build oil pressure, oil pressure switch should close and power the fuelpump, effectively bypassing the relay contacts.

So, if you power the fuelpump as has been discussed and start the engine, the oil pressure switch should close and keep the fuelpump powered up until the engine is switched "OFF".

<img src = "https://i.imgur.com/0KEdRo6.jpg">


Also see wiring diagram linked below.
1990
 
Just grab one of the other relays in the relay/fuse box and put it in the fuel relay spot. That will prove out the relay real quick. Mark.
 
"Just grab one of the other relays in the relay/fuse box and put it in the fuel relay spot."

Mark, that doesn't work on that vehicle, the fuelpump relay is unique to itself on the vehicle, and a "weatherpak-style" connector plugs into it.
 
Bob did you run the engine with the adl test port hooked up to 12 volts? Did it work okay? I'm worried about it back feeding a circuit.
 

Due to the test port being connected to a SPDT relay it CANNOT "backfeed" anything.

If the relay coil remains unpowered, power to the "C" terminal can only go to the fuel pump.

If the problem you are having corrects itself, the relay will switch, leaving your temporary power disconnected.
 
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