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PCM crapped out? Anyone have a loaner?

Pillow

Pillow

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Warrenton, VA
Okay here is an odd one. The '99 Burb crapped out all of a sudden and will not turn on at all. When the key is engaged all the dash lights come on and nothing happens at all when it is tried to start up. No fuel pump, no starter, nothing!

I pulled the ECM-1 20A fuse under the hood and I can get the starter to turn with the key and the lights on the dash go away.

I then put the ECM-1 fuse back in and took out the PCM. Which netted the same result as pulling the fuse. I can get the starter to turn with the key and the lights on the dash go away.

Seems to me the PCM crapped out..?

... I am now missing the "brain" to make the rest work. Anyone have a loaner? For a 99 Burb 4.10 Auto-track :) I just want to see that the PCM is the problem or something else has gone whacky.

FWIW the PCM is a Heath GL4.

Thanks,
 
I plan on calling Heath later today and get their input as well.

Also in none of these scenarios did the fuel pump come on. Must be controlled by the PCM somehow? Which I did not realize.
 
I'm not familiar with the later trucks but could it be the Anti Theft causing your problem?

Leo
 
LP is controlled by PCM and IP is controlled by PCM. But if you get it cranking the LP should come on from the OPS, but IP won't inject anything without PCM.

Your description could be a little more to the point. Are you saying you get no cranking with the PCM attached and powered? But it cranks with PCM not powered? The PCM is controlling the starter?

I dont have an OBD2 manual, to see how IGN START switch gets to the starter, but I didnt expect it goes through PCM. There could be a shorted power wire to the PCM that is pulling all the ignition voltage away???
 
Sorry if I confused anyone in the description.

The starter has no interaction with the PCM in theory. BUT the starter will not turn with the PCM attached. Go figure.

This is an odd one, as I have never heard of one like this before on the forums. But it definitely has something to do with the PCM or PCM wiring.

Also when the PCM is connected and the Key turned to on, all the dash lights light up and stay lit up. Again odd.
 
Need a wire diagram of OBD2 crank circuit, and the PCM to see how they could affect eachother.

Is there something that the PCM could control tranny gear that would prevent starter from being able to turn the engine? Do you hear anything happen, or silence?
 
Neutral, okay I will give that a try.

I have a new ignition switch wiring harness. I tried the old and new one with no difference. That was my first thought on this issue as well, but not so.
 
Not yet.

As for the switch it is part of the wiring harness. So yes, i have a new switch. Again to no avail.

I still think the PCM took a dump... Or some wire is cut in half that I cannot see between the underhood fuse box and PCM, maybe.
 
UPDATE!!! It is ALIVE!!!

... I am ashamed to admit it... The grounding connection from the PCM to the motor mounted ground had come semi loose. You could not tell to look at it, but I yanked one the wire and out it came. After speaking with Bill Heath he claimed that it had to be a ground issue, so I went looking again and found it.

Recrimped a grounding connector and hooked it all back up and presto! Alive again.

Sad and pitiful. Also the oddest failure symptoms I have ever seen for a ground!

Thanks for all the help!!! Beers for all, cheers!
 
It is the ground that is mounted on the passengers side of the engine on a bolt that holds the lower intake manifold on. Yes, it can be a knuckle breaker.

Unless you know where it is, it is hard to spot straight away.
 
Pillow said:
It is the ground that is mounted on the passengers side of the engine on a bolt that holds the lower intake manifold on. Yes, it can be a knuckle breaker.

Unless you know where it is, it is hard to spot straight away.
Click to expand...

Unless you don't have A/C that is. I believe its the 2nd stud inwards from the firewall?
 
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