PCM Control (Re-Post)

Jamey Owner/Technician California Posted   Latest   Edited  
Resolved
Driveability
2001 Chevrolet Silverado 2500 HD 6.0L (U) 5-spd (NV4500/MW3) — 1GCHK23U21F106634
Dies
Stalls
Dies Out-No Spark-No Injector Pulse And No Grams Per Second Reading

This is reposted from the GM Truck Chat. I thought I was posting to everyone AND the GM Truck group, but Tom let me know I was only in one group.

Thanks for your time. 

Jamey

Hello DN. I have a Gm Truck that is making me scratch my head. The truck is not exactly in the best of shape. It has been road hard and hung up wet. I replaced the MAF because it was reading 2 GPS at idle and the IAT was fixed at 67*. I replaced the spark plugs and wires. Plugs were worn down to no electrode remaining. It qualifies for a cost limit waiver for smog. Now, the customer says it has been stalling. It stalled before this repair. I have scope checked the CKP and CMP when it stalls. Both are present at the PCM connector. There is no spark or coil trigger, no injector pulse or trigger. The Tech II shows no RPM, No injector on time and no Grams per second reading when cranking. I do have CKP and CMP at the PCM. 

Sounds like a bad PCM… Well I installed a GM Factory reman. Programmed it and made several test drives. All was well, until it got towed back in. I now have the exact same symptoms when it stalls. If I let it sit for a bit, it will start back up. I have checked grounds, powers, etc. Pulled and tugged on the harness. I disconnected the alternator, I am getting about 1.5 volts AC max. It still will stall. I can just let it idle in my stall and it shuts off. 

I used a heat gun on the PCM, it did not make it stall. I have the hood open and the PCM is not really that warm. I don't think it is heat related, however it always starts on a cold start. Let it run 15 minutes or so and it stalls. 

What am I missing for inputs? When it stalls, I can read data on the Tech II. TPS, ECT, etc…. The only thing that is not changing in the RPM, Injector MS and MAF/GPS. 

Looking forward to some input from the group.

Jamey

0
Lonny Diagnostician
Florida
Lonny
 

Have you checked all powers out from Ignition switch. I had similar Issues with a gently used Tahoe that turned out the ignition switch was losing contact.

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

I will check again. I know I have power at the INJ fuse that feeds the injectors and coils.

0
Ð Awarded
Fred Owner/Technician
California
Fred
 

There has been various cases where a ground gets hot and opens up, causing a variety of problems, scope the powers and grounds while it is running, carefully watching until it dies Fred

0
Ð Awarded
Brad Diagnostician
Washington
Brad
 

This is sage advise. I have seen the ground strap from the back of the cylinder head do this.

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

I have checked the grounds. I loosened them and re-tightened them. I don't think it is a ground problem, because when it stalls, there is still a good CMP/CKP signal and during cranking the signal stays good. I will check it again.

0
Ð Awarded
Brad Diagnostician
Washington
Brad
 

And it isn't throwing any codes correct?

0
Ð Awarded
Mike Owner/Technician
Washington
Mike
 

Isn't there a TSB concerning this. I have updated the PCM software and fixed 1 for the same problem

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

PCM replaced. New current software installed

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
   

It will set lean codes. It has 2 cracked exhaust manifolds. Leaks from intake gaskets. It did set a CKP code before the PCM was replaced.

0
Ð Awarded
Brad Diagnostician
Washington
Brad
 

I may be getting platforms mixed up, but if that has the wire loom that runs across the front of the timing cover and up by the power steering lines and its a oil leaker, I have seen those wires get really gooey and F-ed up.

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Surprisingly it doesn’t leak much oil. The customer said it had an engine installed a few years ago… this problem has started recently. I have fingered the harness pretty good and it doesn’t cause the stall. However my spidey senses are tingling about the harness and wiring. I was pretty busy today and didn’t spend any time on it. I’ll get back to it tomorrow I hope.

0
Ð Awarded
Tommy Owner/Technician
North Carolina
Tommy
 

Jamey, Check the pink wires under the the underhood junction block, and splices S152, S154,& S157. and G114 left rear of engine Good Luck, Tommy

0
Ð Awarded
Robert Owner/Technician
Virginia
Robert
   

You probably have all ready done this unplug mass air flow have had several of these mess with me

0
Ð Awarded
Tom Owner/Technician
Tennessee
Tom
 

Maybe you've already checked, but I didn't see where you verified power to the injectors and coils. Also, I have seen a few of those with badly corroded PCM connectors/harness terminals. Tom

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Injectors and coils have power during no start. INJ fuse good.

0
Ð Awarded
Leonard Owner/Technician
Georgia
Leonard
 

How are you testing the power? Load testing or just a test lamp.

0
Ð Awarded
Raymond Mobile Technician
Michigan
Raymond
 

Try jumper cables both ends on battery negative and other two end clamps on block and frame, I also have seen the ground near under power steering I believe it feeds the harness at coil pack bracket two grounds go into connector on top of bracket, just run auxiliary grounds for testing purposes. HTH let us know

0
Ð Awarded
John Technician
Ontario
John
 

Does it restart immediately?? Can an ignition switch do this after heating up?

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Has to sit for a bit before it restarts. Ignition switch has power.

0
Ð Awarded
John Technician
Ontario
John
 

Believe you said coil and injection power remains whine stalled,do you have drive/ command? If so does it seem to he at the right time? Also, how are these cats doing? Are the heating up and restricting flow?

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

No injector or coil trigger When it stalls. CMP and CKP are good.

0
Ð Awarded
Grant Technician
Illinois
Grant
 

“I replaced the MAF because it was reading 2 GPS at idle and the IAT was fixed at 67*.” What does the replacement MAF and IAT read? Checked Global/Generic scan data for comparison? Please clarify this statement/explain your test because I don't know if I've ever heard of anyone performing this test as you stated: “I disconnected the alternator, I am getting about 1.5V AC max” 1.5volts AC as…

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

The MAF now reads about 6 grams per second at idle and the IAT responds correctly. With the old MAF, it would bog down and not have much power. I disconnected the alternator to remove the thought of too much AC voltage causing the PCM to shut down.

0
Ð Awarded
Grant Technician
Illinois
Grant
 

Maybe I don't understand from your description, but I thought the stall only happens after 15 minutes of operation and can't always be duplicated. Are you disconnecting the main positive thick gauge power wire? I see disconnecting the alternator as something I would do to test for an internal alternator short causing a parasitic draw engine OFF. If the AC voltage on the main power out while…

0
Ð Awarded
Robert Diagnostician
California
Robert
 

Is an injector or coil pulling too much amprage? Thinking back to the Quad driver days when they got too hot and shut down. It would shut down 4 control loads. That would explain why you can still get some data stream and have no spark or fuel injection pulse. The other thing that comes to mind is the ignition switch. They have multiple power outputs and you can lose one and not the others…

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Coils and Injectors have power when it stalls and while it is a no start. I’m going to recheck the rest of the powers from the ignition switch.

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Well, if you've got solid signals from the Crank when it stalls, how's the frequency from The MAF, when tested at the PCM? I believe you said that the MAF also does not respond on the Tech 2 when cranking? If all that is good, double check the powers and grounds at the PCM. Knowing you, and how thorough you usually are, you probably already have. This smells like another PCM, or a bad pin fit at…

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

I’m thinking the PCM is bad. I believe it may have damaged drivers. But so did the last one. What I’m trying to do is eliminate the cause. That is, if I’m on the right track. I didn’t have a chance to work on it yesterday. I will try to get on it today. I have a pretty good technician who can do this, but I have him doing more profitable stuff at the moment. When things get weird, I try to take…

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Doubtful that anything ‘killed’ the drivers, as they're not high amperage stuff on this. The coils have an integrated ICM on each coil, so unlikely that's an issue. And the crank sensor is low amp stuff as well, as is the MAF. I've seen this scenario multiple times, with various total circuit failures. Always has been the PCM. I suppose, that it could be a bad coil shorted to power through one…

0
Ð Awarded
Stephen Technician
Tennessee
Stephen
 

Do you mean that it has no RPM, INJ pulse or MAF reading as it stalls? Cranking after the stall? Do you have the original PCM. I’m thinking , do a fast swap after stall to a cool PCM to see if it will immediately restart. Or wrap the PCM in a cold wet towel. How long is it having to sit before restart?

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Correct on all. No RPM, MAF, INJ when it stalls and when cranking no start after stall. I have not swapped the old PCM to see if it will start. I do still have it.

0
Ð Awarded
Stephen Technician
Tennessee
Stephen
 

I’m focused on the loss of RPM signal. The CKP and PCM are the only devices needed for that. Considering all that’s been done, I really have to wonder if the CKP signal has another issue besides just loss of. Or the PCM has a power issue. How about pull the CKP, heat it with a heat gun, put it back, see if the truck starts. Or get another CKP , run the truck to stall and hot swap the CKP, see if…

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Stephen, I did the hot swap and the vehicle still will not start. I think this can eliminate the PCM ???? I checked the Power Mode data in the tech II, It does show the vehicle is cranking and correctly displays the key position. Voltage shows good. Now I am back to looking for a component or wire that is shorting and pulling “something” low, or maybe in the harness? So far my voltages have been…

0
Ð Awarded
Stephen Technician
Tennessee
Stephen
 

I think the hot swap of PCM , no start, says that the PCM is not the cause. Since the PCM and CKP are the 2 components needed for RPM, I’m more focused on the CKP/circuit. (Then I wonder, could the loss of CMP cause this? Seems far fetched.) CKP are well known for failing when hot. I wouldn’t expect wiring to be repeatably heat sensitive.

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
   

Besides scoping the 3 or 4 separate power feeds, throw a lead on the Class 2. You mentioned random comm codes on the phone, and now I wonder if a stray voltage spike through the Class 2 is like a Phaser stun to the processor.

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
   

When the truck stalls, I have Class 2 Data on pin 59. Battery voltage on pin 58 Should pin 58 have a data transmission?

0
Ð Awarded
Timothy Owner/Technician
Wisconsin
Timothy
 

Yes, pin 58 should have data transmission. 7.5V square wave. Something very weird going on there, if you've got something resembling data on 59…

0
Ð Awarded
Jamey Owner/Technician
California
Jamey Resolution
   

Well….. I will call this truck fixed. I put a crank sensor in it and now it does not stall. I did see that the old sensor did not pull all the way to ground. I tried to add a ground and it did not make a difference. I now owe Bob Augustine lunch, he told me to put a crank sensor in it a week ago. I said WHY? I have a crank signal. He said he had ate his lunch on an old GM 3800 with the same…

+1
Resolution Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

That's pretty funny JT. I have watched diag videos and been shouting at the screen "it's not pulling to ground" before that was pointed out as the issue, and the lesson of the video. I would blame Pico...LOL...hard to see where ZERO is when you don't put cursors on it. SO always had that grid. I think you click the reply/edit button in your OP and one of the choices is to mark it resolved.

+1
Ð Awarded
Robert Diagnostician
California
Robert
 

If it was posted as a question, then there is a resolved button. A discussion does not have it.

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

10-4

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

The weird thing is, I knew it wasn’t pulling to ground, but the vehicle ran with that pattern. When it was cranking and not starting, the signal voltage peak was lower, because it was cranking. But the low pull was the same. I back probed the ground signal and it didn’t change the low pull. Maybe internally the magnet can’t pull it low when the trigger wheel passes by?? WTF?

0
Ð Awarded
Robert Diagnostician
California
Robert
 

I had a similar issue with my 83 jeep on the ignition module and bad grounds that cause a voltage shift and no spark. Little things that can eat our lunch.

0
Ð Awarded
Geoff Diagnostician
Hawaii
Geoff
 

It's almost like when the ECM is "fresh" and in a good mood, it doesn't mind the weak/bad CKP sensor. Then after a while the ECM says, "I'm sick of dealing with this crappy sensor". Obviously if it never ran at all there would have been nothing to think about.

0
Ð Awarded
Robert Diagnostician
California
Robert
 

Thanks for the update! But now we know what to look for in the scope pattern the next time.

0
Ð Awarded
Robert Diagnostician
California
Robert
 

It is a discussion and so there is no resolution to it. It is how you entered it when you made the post.

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Got it! Thanks

0
Ð Awarded
Scott Manager
California
Scott
 

Hi Jamey, I edited the original post by changing the message type to a question which then provided that option in your reply.

0
Ð Awarded
Jamey Owner/Technician
California
Jamey
 

Thanks Scott. I didn’t know that the discussion topic didn’t allow for an answer.

0
Ð Awarded
Donny Owner/Technician
Mississippi
Donny
 

I know this is an old post, but 9 times out of 10 its the G103 and 104 grounds on top of right head and between head and firewall on left. Fixed many of them. Future refrence…..

0
Ð Awarded