[Rcher]

A week or so ago I had a glow plug tip break off in one of my cylinders which caused my truck to missfire and throw a code. The story is here: http://www.dieselplace.com/forum/showthread.php?t=67545

After a week of conversations with forum members and several GM tech's I pushed for a compression test to check for internal damage before pulling a head.

GM tech hotline claims that *minimum* compression cannot be less than 300psi in any cylinder and to do the test, the key had to be cycled for 6 compression strokes.

The highest reading we got was 360psi and the lowest was 315psi. GM claims that there can be a 50psi differential on this engine. All 8 cyls must be tested and then averaged out. My average psi was 327psi. This is well within GM specs and is above the minimum of 300psi.

I was surprised to hear that a 50psi variation was normal. I also was surprised that the cylinder that *ate* the glow plug tip tested at 340psi and the lowest cylinder was not even a suspect.

The bottom line:

GM tech hotline said I should have no worries about internal damage from the missing glow plug tip and *not* to pull the head(s). They feel the tip got pulverized and sent out the exhaust valves and thats why I had the engine misfire. The turbo is performing normal and engine is running fine. I will drive it and pray I have no other problems and if I do, its all documented and is under warranty for 5/100k.

I wanted to post these compression results so others could have the information if they need it.

Thanks to all who had given advice and input and good luck to others who may have this problem.

 

[seanosu]

Might want to check your exhaust side turbo vains for damage when the tip went through it.

 

[jbdmax]

A 50 psi difference is normal from most engines i have dealt with, but the G.M. bulletin i read here says if the tip is broken the heads must be removed and the pieces found,G.M.'s words not mine, it is here in one of these posts, i would not want my heads removed either but you need to know where those pieces went and that they did not damage anything else. don't need any more problems even if it is covered for 5 year/ 100,000 miles. might only make it to 50,000 in 5 years depending on how you use your truck. the G.M. tech line is blowing smoke up your a$$. just my opinion, hope that it all over and that the pieces are gone.

 

[Carmine LBZ]

Too bad about your engine giving you grief. I just went through the same thing with mine with 2 glow plugs that were both on the same bank. The did pull the head and found nothing wrong, which didn't surprise me. After they broke off and cause my truck to miss almost violently, the engine ran perfect. No rough idle, no lack of power, no change in miles per gallon. This is more than likely the same case with you. Good luck, and I hope you have no further issues. BTW, I just got mine back, and with one very small exception, she runs fine...Carmine

 

[geabis]

I wouldn't be surprised if GM posts a new tsb on the glow plug issue stating exactly what tech line said am assume they are seeing labor costs soar on the repair and finding out that every time they pull the head that there was no reason to do so.

thanks for keeping us posted

Good luck

 

[Joey D]

I would think pulling an injector and using a fiber optic scope would show you if a piston had damage. I would do that before pulling a head.

 

[Rcher]

I would think pulling an injector and using a fiber optic scope would show you if a piston had damage. I would do that before pulling a head.

We did, no signs of internal damage was found.

Carmine,

Glad to hear you got your truck back and no damage was found. Now I hope they get it running as good as new again. That was a fear of mine if the head(s) needed to be pulled. Good Luck!