# 1994 k-3500 fuel pump issue



## bassfishn1 (Jan 14, 2008)

i have an issue with my fuel pump i think, very frustrating, and colddddd
codes 42,54,74,85,86, i know some are my tranny issues that still need to be adressed, but the 42 is stumping me, or i am missing something
truck won't start, replaced fuel pump relay, and fixed the bad ground, truck started fine, test drove it, no problem, let it be for the night, go out to start it the next day, nothing, just cranks. checked the fuel pump fuse, it's good, replaced with new one anyways, have power in and out of fuse, have constant power, with key on, at the relay on the orange wire, nowhere else.
checked the plug at the pump, no power there on any of the 3 wires
where to go now? maybe the ecm?, not sure how to test that, but code 42 says it is a possibility?, any help would be appreciated, ty


----------



## B&B (Nov 4, 2006)

Take a 12V jumper wire with a 15 amp fuse in it and connect it to pin "G" in the OBD1 connector under the dash. You may need to unfasten the connector from its mount to read the lettered pin identification markings on it. MAKE SURE YOU GET THE CORRECT PIN WITH THE JUMPER WIRE.

Does the FP run as long as the jumper is connected?


----------



## bassfishn1 (Jan 14, 2008)

do i jump from g pin to ground?


----------



## bassfishn1 (Jan 14, 2008)

and is this with key on or off?


----------



## bassfishn1 (Jan 14, 2008)

ok, put power to the g pin with fused jumper, got power to the pump on the white wire at the under truck 3 pin connector, still have power at the fuse, still have power at the relay on orange wire at relay, and with key on, jumper attached, have power at both orange, and red wire, at the relay, checked 2 gray wires at the ecm, no power with key on, or off, and with jumper wire both connected and disconnected, not sure if i tested the right wires there?


----------



## bassfishn1 (Jan 14, 2008)

just to let you know, did not connect the 3 pin connector to the pump, not sure if this matters, but i did not have power before to the connector, so figured it was not necessary, let me know if i am wrong?
actually i will connect it when i go back out there, it's so damn cold though, gotta warm up the bones first


----------



## nelson4047 (Dec 7, 2008)

grey wire at the pump will only be hot for a few seconds after you turn the key on, or you need to have someone crank engine. best to ckeck between the grey & black that way you are checking your ground also. if no power you need to go back to the relay & make sure the ecm is grounding the (i think its a green wire ) to turn the relay on


----------



## B&B (Nov 4, 2006)

bassfishn1;666942 said:


> ok, put power to the g pin with fused jumper, got power to the pump on the white wire at the under truck 3 pin connector, still have power at the fuse, still have power at the relay on orange wire at relay, and with key on, jumper attached, have power at both orange, and red wire, at the relay, checked 2 gray wires at the ecm, no power with key on, or off, and with jumper wire both connected and disconnected, not sure if i tested the right wires there?


Your making good progress. Jumping the G pin and having power at the plug tells you that the wiring and its connections are good from the relay to the FP.

Now what you need to do is see if the dark green/white wire at the relay has power. This is the relay trigger signal from the ECM. It will tell you if the ECM is actually commanding the FP relay on...which it should for approx 3 seconds after you turn the key to the run position, or anytime while cranking. if the drk green/white wire never trips the relay then either that wire connection is poor at the ECM, the ECM fuse in blown, or the ECM itself is defective.

Also check the black/white ground wire at the FP relay for a good ground. Have seen then fail to supply ground to the relay before and cause the relay not to energize.

See what you find....


----------



## B&B (Nov 4, 2006)

Also, give me a little time and I'll see if I can dig you up a wiring diagram for the FP circuits for your specific truck. If I can, I'll post it. Should help you to understand the system.


----------



## bassfishn1 (Jan 14, 2008)

tnx, gonna give that a go this morning.
where is the ecm fuse? is it actually inside the ecm, or elswhere?
and also, with my other codes, i am suspecting the ecm being defective, would that be a good guess?
or maybe these could be sepearate issues?
again, tnx, will try this test this morning and see what happens.


----------



## B&B (Nov 4, 2006)

The ECM fuse (or fuses, some have 2) will be in the fuse panel where all your other fuses are located. 

As to all your other codes, most of them are trans related as you know. And the one is ignition related that does have a possible cause of a bad ECM. 

And yes the ECM can be bad...but I'd suspect a poor ground first, before condemning it specifically. 

If you put your 12V jumper in the G pin on the OBD connector to run the FP, plug the fuel pump connector back together, and attempt to start the truck will it run? Did you try?


----------



## bassfishn1 (Jan 14, 2008)

no, did not try that, but i will when, and after i do the other test? and i did check the ecm fuse at the panel, it was good, but i will put a new one in to be sure
tnx again, i was also thinking about that ground strap near the filler hose under there, did not look too good either, might as well replace that while i am under there
tnx again , been a big help to me, will let you know what happens


----------



## B&B (Nov 4, 2006)

Follow the first procedure I described first so you'll know if the ECM is even commanding a FP request.

And then if you want to see if the truck will even run, add the jumper and reconnect the FP connector to see if it will.


----------



## bassfishn1 (Jan 14, 2008)

yup, that was my plan, tnx


----------



## Sharper Edge (Jan 26, 2005)

I had the same prob. on my 91 3500 changed the fuel pump and all the headaces of the other codes for the trans It was the ECM fixed every thing. and was cheap at Auto Zone. Good luck


----------



## bassfishn1 (Jan 14, 2008)

so what your saying is that you changed both?, or was it just the pump?


----------



## bassfishn1 (Jan 14, 2008)

all the tests i did checked out fine, but still nothing
can't get the pump to go on, even with jumper wire. thinking the pump is shot now
got power to the green/white for like 10 seconds, that should be normal, so pump?, or ecm?


----------



## B&B (Nov 4, 2006)

If you have power on the green/white for a few secs then the ECM IS commanding the FP relay and you should hear it click on, and then off after a short period of time. You should also have power on the gray wire back at the FP connector during this same time. If you do, and your ground is good at the FP connector as well then you either have a FP problem, or a problem with the connector pins themselves.


----------



## Sharper Edge (Jan 26, 2005)

I changed the pump but that did not cure the problem. Then I changed the ecm that was the problem for me not sure what you have. But good luck If B&B can't get you through i your in real trouble....


----------



## bassfishn1 (Jan 14, 2008)

yup, i heard the ckicks, on and off, either way the tanks coming down, haha, in the pouring rain too, sheesh, that one time it started must have been it's last burst
anyways, will let you all know how i made out, tnx again for your help


----------



## bassfishn1 (Jan 14, 2008)

well, got the pump done last night, finally. had some bad weather here for a few days so it took longer than i wanted. was definaley the pump fried, so bad that the wires were melted, antways gonna have to do the whole assembly, new lines and all, probably the tank is gonna have to be refurbished also, but it will wait till spring, i hope
i kept getting that code 42 again after everything was back together, but as i was putting the cover back on under the hood where all the relays are under the hood, i found that i had a short in that wire you disonnect when you set the timing, so that will get fixed today, and we will see what happens from there as far as the other codes go, thanks again for the help


----------

