Compression test readings '93 BRMW - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 06-09-2012, 05:33 PM   #1
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Default Compression test readings '93 BRMW

Rough running, surging at idle when cold. All sensors replaced, throttlebody rebuilt, new intake manifold gasket, new distibutor incl. ignition module.
Pulled all sparkplugs, kept in order of cylinders they came out of. All looks normal (greyish/tan).
Did compression test today. Wide open throttle, all plugs removed.
7 compression strokes each.
#1 , #2 , #4 , #6 , #8 -----all reads 180
#3 -----reads 215
#5 , #7 ----reads 175
Why is #3 so high? Do I need to pull the head (left side) ? carbon build up? Can anything fix it without removing head?
Have not done a leakdown test as I am not sure it will tell me much about high comp in one cylinder.
when I bought the car a few years ago, I found the exhaust lifter rod MISSING in #3 . I replaced and it seemed fine for a long time. I recently checked adjustments on all valves, and at the same time checked for, and replaced all rods with even a slight bend. #3 exhaust was one of them.
Could carbon build up possibly hit the valve?
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Old 06-09-2012, 08:03 PM   #2
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Seems like your exhaust valve may not be opening all the way. I see a history of valve problems on #3. I'll bet the valve is bent.
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Old 06-09-2012, 08:17 PM   #3
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Danthurs......If the valve indeed is bent, it would have to be on rocker arm side of head? With high reading on this cylinder, I would assume it does close fine. Is it possible to determine this without removing head?
You mentioned noticing a history regarding cyl #3 .....could you explain/detail?
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Old 06-09-2012, 09:12 PM   #4
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Quote:
I found the exhaust lifter rod MISSING in #3 . I replaced and it seemed fine for a long time. I recently checked adjustments on all valves, and at the same time checked for, and replaced all rods with even a slight bend. #3 exhaust was one of them.
I would look real close at the rocker. To check the valve you would need to remove the head and pull the valve out.
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