No Compression!.... - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect

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Old 03-31-2010, 05:41 PM   eBay Motors  #1 (permalink)
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No Compression!....

i have no compression in cyl. 6. Any ideas? Whats most common cause on these engines with a cyl with no compression?
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Old 03-31-2010, 05:43 PM   eBay Motors  #2 (permalink)
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Broken piston rings
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Old 03-31-2010, 05:44 PM   eBay Motors  #3 (permalink)
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Quote:
Originally Posted by dslkraz View Post
Broken piston rings
Really? Are you sure they dont seal themselves back up with the piston moving up and down?
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Old 03-31-2010, 05:45 PM   eBay Motors  #4 (permalink)
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Broken piston rings
Hmmm, or the more common hole in the piston. even with broken rings you would still have some kind of compression, not alot, but some.
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Old 03-31-2010, 05:57 PM   eBay Motors  #5 (permalink)
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You poppey a holey in the peeston. Broken rings will still make some compression like the others stated above.
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Old 03-31-2010, 06:02 PM   eBay Motors  #6 (permalink)
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Did the gauge not try to move at all, or did it flutter a little? Or is your gauge reading 0 and not even trying to climb.

I know you said no compression, but some say no compression, but they really have a little
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Old 03-31-2010, 06:11 PM   eBay Motors  #7 (permalink)
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Ok so its a hole in the piston. What happened up till then I'm just curious, drivin like you stole it or normal driving what's the story?
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Old 03-31-2010, 06:28 PM   eBay Motors  #8 (permalink)
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i would imagine that the cup isnt sealed, since you just had it apart.
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Old 03-31-2010, 06:36 PM   eBay Motors  #9 (permalink)
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heres the story, i dont drive it very hard, i commute 110 miles a day to work. truck started smoking heavy greyish and was knocking around 2000 rpm at cruising speed, when the engine was warm. with the engine cold it wouldn't knock and ran ok other then smoking. i took it in to one dealer to have injectors tested and they said it had blown head gaskets and the injectors were "fine". I did NOT believe it had a blown head gasket because it had no symptoms of that, went to another dealer and had injectors tested and 7 of the 8 had high balance rates and after they cleared the codes and did whatever they did to test it made it run rough all the time but no knocking on the way home. so i bought 8 reman injectors and installed them, got it back together fired up and still runs rough, like running on 7, with light smoke. I scratched my head for a bit and went out into the shop and noticed that 7 of the 8 injectors i took out had the washers still on them and cyl 6 injector does not, (which is the cyl with no compression) and i do not remember the washer falling off the injector on the way to the bench nor did i hear it drop off. I know for a fact i installed 4 new washers on the drivers side so i may have 2 on cyl 6 injector but i dont think this would be my problem since the injector should still be seated on the washers to seal, maybe im wrong. so i took the truck to a shop that the owner/mechanic use to work for GM for 20 years or longer and he plugger in the tech 2 and cyl 6 balance rate was +15, cyl 3 was 0.3, and the rest were -7. he pulled cyl 6 glow plug which the tip was like melted off he said and did compression check and nothing, and this is where i am at.
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Edge Evo Race :rockin
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Old 03-31-2010, 06:38 PM   eBay Motors  #10 (permalink)
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also, i had no cups pull out of the 8 but that cyl. 6 cup when i touched the edge i noticed would kind of 'rock' side to side but it did not pull up at all.
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04 GMC EC/SB LL7 De-Badged
Swapped LB7 to LLY
Edge Evo Race :rockin
4" Straight Pipe
LBZ M.P
EGR Blocked


I.B.E.W Local 1547

Last edited by akduramax; 03-31-2010 at 07:07 PM.
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