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The Great Kruso
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3,876 Posts
Discussion Starter #1
Well....i finally bit the bullet and swapped out some parts which i thought were the cause of my car missfiring, but nothing made a difference. Went and baught a compression guage, 150 accross the board except for the last two cylinders. Before the dallas meet, the compression was 160 accross the board in all the cylinders. The car did 260 to the rear wheels on stock turbo and boost. Its definitely not the head or the valves, because since noticing the problem, i've changed the whole head. Why would I have lost compression on the last two cylinders on a brand new internal motor which was maintained regularly, any ideas??? Not really liking the idea of taking the motor apart again, so i'll probably end up taking the rings out while the block is still in the car.

Kruso

btw, the compression was 40 psi in the last two cylinders
 

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wastegate hose is pulled
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4,586 Posts
A cylinder leakdown test will determine where your lost compression is going. You could put a bit of oil in the cylinders and see if compression comes up, but I haven't found that to be a reliable indicator (of bad rings).

Of course there is always the obvious BHG.

Piston rings don't like detonation and you may have broken a couple or even burned the pistons. This can happen regardless of mileage on the motor. :(
 

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boost freak
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10,042 Posts
eh. attempting to pull pistons w/the engine in car is retarded- you have to jack the engine way up to pull the oil pan.

that said, redo the compression test w/some oil in the cyls to see if its ring related. if that doesn't help, then its dead pistons or valves....
 

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The Great Kruso
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3,876 Posts
Discussion Starter #4
drjonez said:
eh. attempting to pull pistons w/the engine in car is retarded- you have to jack the engine way up to pull the oil pan.

that said, redo the compression test w/some oil in the cyls to see if its ring related. if that doesn't help, then its dead pistons or valves....

Thanks for the response:rolleyes: but I've CHANGED out the rings before in a day, and NO the engine doesnt have to be lifted up "way up high" Just the cross member needs to be dropped with the three bolts on each sides and the two engine mount bolts.

Your second theory....the whole head has been changed out with a perfectly good head, thus it CANNOT be the valves. When I replaced the head, I didnt see ANY let alone any serious damage to the cylinder walls, indicating any breaking of the rings or pistons.

Kruso
 

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The Great Kruso
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3,876 Posts
Discussion Starter #6
chevyeater-on-sf said:
There was no cylinder wall damage with my broken ring.
Interesting....all the great ones have said there's almost always wall damage. Could you describe to me what you found when you got to the core of the problem? Was your piston broken? and absolutely NO damage to the cylinder walls???? Thanks

Kruso
 

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wastegate hose is pulled
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4,586 Posts
The piston wasn't broken. After I got the engine out of the car and on a stand I was able to see some VERY minor scuff marks on the cylinder wall that were not in the other cylinders. It still felt smooth to the touch and was not measureable.

I think that rather than butting end gaps, wich is the normal failure mode, my ring shattered. No definitive cause was found. I've got some theories but that's it. Sure wasn't an assembly error, it ran perfect for 192,000 miles prior.

I'd seriously recomend a leakdown test before you tear into the engine again. 40 psi cranking compression means there is a serious leak somewhere. The leakdown test will make it abundantly clear where.
 

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The Great Kruso
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3,876 Posts
Discussion Starter #8
Might be so, but my PCV's are thowing out white smoke and oil at high RPM's as if they were the oil pump. So that pretty much narrows down the whole problem.

Kruso
 

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boost freak
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10,042 Posts
yeeep, dead piston.

as for doing stuff in car, to each their own. i see it as a HUGE waste of time. pulling the engine is quick enough....
 
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