Compression test 30psi :( all cylinders... - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 07-25-2006, 09:02 PM   #1
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Default Compression test 30psi :( all cylinders...

My friend just bought a 92 bonneville sse (non-supercharged) and it was ideling rough and stalling. The guy he bought it from said one of the coil packs was bad and needed replaced.

So I'm over here working on it with my dad, and one of the coil packs is cracked, so I go buy a new one and while I'm at it figure I'll put all the usuall maintence stuff in it. Plugs, wires, fuel filter, air filter, and while I'm changin the plugs I'll do a compression check.\

30psi... all cylinders.. wet test bumps it up to 40psi.


From doing a search on here and seein the 150'* I'm guessin 30 aint too hot...

So what do I do now?
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Old 07-25-2006, 09:25 PM   #2
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How many miles are on it? 30 lbs. is not very good, that'* for sure. Are all of the cylinders 30/40?
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Old 07-25-2006, 09:54 PM   #3
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100,000... yeah all of em but #4 actually go to 60psi.
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Old 07-25-2006, 09:55 PM   #4
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So after several strokes it still didn't come up over 30 PSI?

I wonder if this car suffers from the Burnt exahust valves...


And like asked, how many miles on the motor?

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Old 07-25-2006, 11:05 PM   #5
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jr, he already answered that
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Old 07-25-2006, 11:42 PM   #6
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Quote:
Originally Posted by Jaysik
100,000... yeah all of em but #4 actually go to 60psi.
assuming that its 100k even...which is pretty good for a 92..
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Old 07-26-2006, 12:00 AM   #7
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Default Re: Compression test 30psi :( all cylinders...

Quote:
Originally Posted by Jaysik
So what do I do now?
30 to 40 psi, with a high of 60 psi is pretty well sucking.

Good news is the wear sounds pretty even (it'* not like one is dead and the rest are good)

Probably needs a valve job on both cylinder heads. A 10 psi bump wet is about right for the rings, so yours are probably OK along with the cylinder bores. I'd be looking at doing the just the cylinder heads. Price tag on remanf is about $220 per head plus another $100 in gaskets if you are D.I.Y. inclined.

Cleaning and lapping the valve seats yourself is an option to explore first if you don't mind having the car down for a few days. Worst case being you find the heads are in need of serious attention beyond the D.I.Y level (like new guides or seats) at which point you bag it and buy remanf heads. (Nothing lost in looking except the time to tear down the heads to inspect the valves, seats, springs, and guides.)
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Old 07-26-2006, 12:13 AM   #8
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Jaysik

Before you do any thing else test the compression again with another compression tester.
Always suspect your equipment when you have strange readings no mater what name is on the equipment.
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Old 07-26-2006, 01:30 AM   #9
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Thanks for the quick replies guys, much appricated. Pretty confident in the equipment but will double check it on another vehicle, cant hurt .

As far as the heads that pretty much reaffirms what I was fearin, but I'm just glad its the top end and not the bottom, shouldnt be too much to rip em out.

Think i'd be ok going the salvage route for the heads? My buddy really doesnt have all that much cash to be dumpin into it, pretty much spent all of it buyin the car only to have it in this state 3 days later :(.

I'm assuming this is the major factor in why it wont idle and stalls, correct?


once again, thanks!
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Old 07-26-2006, 11:26 AM   #10
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I'd test it with another gauge before tearing it down.

Also:

You did block the throttle body open, right?

Next, take a reading on all cylinders and then squirt some WD40 into the cylinders. Read again.

If the compression jumps quite a bit, the rings are worn. If not, it'* a valve seal problem.
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