Help with fuel pump circuit!

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Zwelder

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Howdy everyone,
I dun messed up and could use some help. In an effort to find a fuel line leak I tried to jump the fuel pump. I jumped the same pins as on my old gmc 87 and 30 which was dumb, the jump wire got pretty hot I pulled it off. Then I jumped the right pins pump worked fine, I found the fuel leak but truck won't start any more. Any ideas?
Thank a lot?
 

MikeT

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Sounds like you shorted something out. Hopefully just blew a fuse, check them first, if no go check for a burnt wire. Good Luck.

Mike
 

crash68

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You sure it was 87/30 you jumped to get the pump running? Those should the correct pins as 85/86 are the coil circuit. If you jumped to the coil circuit it possible you burnt something on the TIPM
Use a meter to check for continuity and/or power on the relay terminals. If you have resistance on the fuel pump circuit to ground the problem is most likely in the TIPM
 
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Zwelder

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I may have shorted 87a and 30, or maybe even other combination. Its been a couple months. I checked all fuses on the box, I don't think there's any more fuse boxes in these trucks , right? This truck was gifted to me by some friends whom I helped out before, I got another truck to get around fortunately.
I tested the fuel pump, it runs just fine. Is it worth trying to pull apart that TIPM? Or just try to find a used one? It seems it just bunch of connectors I'll have to unplug from the bottom to unhook it? Totally integrated, means just that, all relays are in that box?
Thanks again!!


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alnelson14

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You probably jumped 30-86. 30 should be your constant hot, and 86 (or 85) should be your ground on the coil circuit.

Do you have a meter? 85 or 86 should be grounded, and the other should see +12 volts when the key is on.

Im betting you melted a ground as the wire to terminal 30 should be more robust than the wires to pin 85 and 86.

How to test- with the key off, and the meter set to ohms, find a good chassis ground and probe pins 85-86. One should take the meter off OL (OL means its open. it means theres infinite ohms of resistance and theres no continuity) It should go to ~0.0.

If there is no good ground, you still need to find which terminal is power to the coil circuit and it should be the switched side. set the meter to DC volts (the symbol is a solid line with a dashed line under it) and reprobe pins 85-86. One of these SHOULD have power. The other will be your ground.

If there is continuity to ground but NO voltage, it is sadly probably your tipm. If everything else works, you can wire up something to run the fuel pump without replacing the tipm.

If there is NO ground but voltage to the other leg, the quick and dirty way to get you back on the road is to stick a piece of wire in the terminal on the fuse box that should be ground, stuff the relay in, and ground the other side of that wire.

Lots of stuff i left out. I dont intend to come off like i think youre an idiot. I just dont check here often and had a few minutes.

And 87a is the normally closed pin on the relay. If you look at your fuse box, its the hole without a pin in it.
 
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