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Discussion Starter #1
Today after work I went out to start my truck. It started right up as usual. I was parked with the front end slightly downhill and the outside temperature was 40 degrees. As I put it in "D" and started slowly driving thru the parking lot, a "major" engine knock started and the engine started to miss. It sounded like there was a 3/4" wrench flopping around in the motor. I checked my oil pressure and it was over 60psi. I immediately shut it down. I waited 20-30 secs and restarted. I noticed that the glow plug light stayed on and wouldnt shut off. I turned off the key and re-tried again. Same thing, the glow plug light wouldnt turn off. I went ahead and started the truck anyway and it fired right up but the engine knock was still there and also had a miss. Being theres only 2300 miles on the truck and under warranty, I drove it anyway checking oil pressure and listening carefully to the knocking noise. Oil pressure was good. After about a 1/2 mile down the road the noise seemed to disappear and no more missing!

I have a couple of questions:

  1. If a glow plug was starting to fail (or failed) would the engine make more noise than if it was running on all 8? It sounded like an older PSD or Cummins.
  2. I have no CEL or SES lights on. If there was a serious problem, wouldnt this set off a code?
Since I have gotten home tonight I have started the truck several times and it runs perfect and sounds normal. How do I explain this to the dealer? Can anyone help me make sense of this?

:help:
 

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Quote: Since I have gotten home tonight I have started the truck several times and it runs perfect and sounds normal. How do I explain this to the dealer? Can anyone help me make sense of this?


This sounds like a pain in the a**, but if your dealer lets you drop the truck off the night befor, let it sit overnight and the next morning be there when they open and start it up with the tech with you to duplicate the problem.
 

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Discussion Starter #4
Update

This morning I went out to start my truck and let it warm up before work. It was 16 degrees and I hate jumping into my truck with cold leather so normally let it run on the elevated idle for 10 mins before leaving.

I turned on the key and the WTS (wait to start) light never shut off. I cycled the key on/off a couple of times and it stayed lit. I started the truck anyway and fired right up. No engine knock this morning. Now, I have a CEL (engine symbol) lit.

I have limited dealer choices where I am but plan to take it in this morning and see if they have a Dmax tech. I am traveling with work and am a long ways from a large dealership.

Any idea's as to why this is happening?
 

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Any chance the glow plug controller is staying on, and burned the end off of a glowplug? The burned glowplug banged around in the cylinder until it was blown out the exhaust. This could explain the knock that went away. There is another thread in the LBZ section that talks about an engine that had to come apart with less than 10 miles on it because glow plugs broke.
 

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Discussion Starter #6
Any chance the glow plug controller is staying on, and burned the end off of a glowplug? The burned glowplug banged around in the cylinder until it was blown out the exhaust.
If the glow plug burned off, wouldnt it continue to missfire? Its running fine this morning but the check engine light is on.

I think the dealer metioned he would check the glow plug module.
 

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The miss could have been caused by the end of the glow plug being stuck under the valve, holding it open. Then it quit missing after it exited the cylinder. Just speculation, I don't know that any of this happened.
 

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According to my service manual, each glow plug is controlled individually and can be diagnosed individually. So, if a glow plug is burned out, it should show up as a circuit fault with a code.
 

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Discussion Starter #10
Update #2

The dealer pulled one code from the ECM .. PO671. this code pertains to the bulletin of January 26th with the "fast open glow plug" and the "slow open glow plug" problem. The tech claims this is a "fast open" condition and would only require replacing all 8 glow plugs. He did not clear the code because he wanted it to develop a history? Glow plugs are on their way and will be here in the morning, the tech will replace them as per the bulletin.

Hopefully he's right on his "fast" diagnosis and I dont have a "slow" condition. The "slow open" condition would mean that a glow plug end has broken off and the heads would need to be removed to clear the chambers of the debris. I really hope he's right. I dont want my heads pulled for a glow plug problem.

I will post complete replacement results after I get my truck back tomorrow.
 

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The dealer pulled one code from the ECM .. PO671. this code pertains to the bulletin of January 26th with the "fast open glow plug" and the "slow open glow plug" problem. The tech claims this is a "fast open" condition and would only require replacing all 8 glow plugs. He did not clear the code because he wanted it to develop a history? Glow plugs are on their way and will be here in the morning, the tech will replace them as per the bulletin.

Hopefully he's right on his "fast" diagnosis and I dont have a "slow" condition. The "slow open" condition would mean that a glow plug end has broken off and the heads would need to be removed to clear the chambers of the debris. I really hope he's right. I dont want my heads pulled for a glow plug problem.

I will post complete replacement results after I get my truck back tomorrow.
the only way your engine would sound like there was a 3/4 inch wrench flopping around inside the engine would be if the end of the glowplug broke off and fell on top of the piston, if was just burn't out and only one was not working you would never know except for a possible slight skip on start up, have seen 8 cyl. diesels with 4 or 5 burnt out and customer did not know, would just say i thought it was a liitle hard to start. make the sure they check the ends of the plugs and don't just pull them out and change without looking. have seen some mechanics in a hurry skip right over a problem on removal because they were not paying attention.
 

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Discussion Starter #12
the only way your engine would sound like there was a 3/4 inch wrench flopping around inside the engine would be if the end of the glowplug broke off and fell on top of the piston
This is a small dealership and I plan to stand there and watch him pull the inner fender wells and then pull the glow plugs. I will certainly be aware of the condition of the existing plugs when he removes them. Thanks for the insight. I have already contemplated this repair procedure and plan to be there for it.
 

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I recently had same problem and it ended up needing a motor as there are not enough part to repair at this time i would suggest they look in cylinder with bore scope
 

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Discussion Starter #14
Update #3

Ok, here's the total scoop.

The dealer replaced all 8 glow plugs as per the bulletin. Cylinder #4 did have a glow plug that was missing a portion of the tip and had an open circuit, hence the CEL and WTS light failure. The tech removed the injector and used a bore scope to view the cylinder bore, piston head and everything else that was possible to see with the scope and could not find any evidence of scratches, dings or any scoring of the piston or cylinder walls. He thinks the piece broke off and was ejected from the cylinder almost immediately or disintegrated into particles and went out the exhaust. He cleared the CEL and so far, everything is fine. Power and boost seem normal.

I know, the bulletin said to pull the heads if any piece of a plug was missing but the service tech called the GM tech hotline and whoever he spoke with told him that as long as they confirmed with a bore scope that no damage had been done inside and the debris is gone, chances are it will be fine.

I hated to have a head pulled at a dealership .. and here's my comment on that ....

I personally dont feel that any shop would ever be able to do as good of a job performing this procedure as the engine assembly line in the factory. There are always little tid bits of things that never seem to work the same as the original assembly after a procedure like this. I make this statement based on my previous life as an ASE certified mechanic.

I have 2400 miles on this truck, 97,600 miles left on engine warranty. If the engine pukes or dies, it will be under warranty. I usually trade every 3-4 years anyway. I'm hoping for the best. I spoke to all of their techs (5) and the service manager who also looked in the bore scope and told me they would not have a worry if it was their truck. Thats alot of eyes and opinions that were involved.

The thing I have a problem with is that the glow plug part numbers of the new plugs are the same as original. Now how does GM expect these to perform any better than my old ones? This tells me they (bosch) has a bad batch of plugs and isnt doing anything about it. All 8 of the glow plugs showed signs of corrosion on them and were totally carboned up after only 2400 miles. Something caused the plug to lose a piece, faulty plug? Nobody can tell us that or that this problem wont happen again.

"I'm gonna drive it like I stole it" :exactly:
 

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I had the same code and probably have the same problem except mine never made a nocking sound. Hopefully no major problems and can have it fixed fast.
 

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Rcher,
I don't believe this is a glow plug problem, it is a controller problem. No glow plug will live if kept energized for long periods of time. I would make them replace the controller before it happens again. You said the light stayed on for a long time. A repeat performance will probably ruin something for sure.
 

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Discussion Starter #17
Rcher,
I don't believe this is a glow plug problem, it is a controller problem. No glow plug will live if kept energized for long periods of time. I would make them replace the controller before it happens again.
I understand what you are saying but the bulletin states specifically not to replace the GPCM. Dealers have evidently returned them already and they have tested out ok. I will call my dealer and ask him. Thanks for the heads up. :think:
 

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glad to hear no problem upon visual inspection, we hooked a glow plug up to a battery to see how long it would burn before dying, unhooked after 24 hours as it was still working. they are pretty tough. but have seen industrial engines swallow glow plug tips before also without causing any signifigant damage. would not like my new engine taken apart either unless absolutely necessary.
 

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I could understand GM not wanting to replace the controller if there was no evidence of prolonged on time, but why wouldn't they do it when you said the light stayed on? I guess if they are willing to put a motor in it instead of a controller, don't worry about it.
 

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I'd like to see someone do that test with a Dmax glow plug. From what I read in the manual, these draw lots of current and get really hot. That's why they don't have to be turned on long like they used to in older engines.
 
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