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1984 500 sel
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61 Posts
Discussion Starter #1
i tuned my car up because of a rough idle, but while all plugs were out i did a compression test on all cylinders. all four on the drivers side tested around 150psi (only cranked over a couple of short times) but the passenger side tested around 130 or so. my question is would this indicate some sort of leak on the pass. side because the old plugs look a little black and sooty on pass. side as well. and the driver side plugs look pretty nice as in firing proper (no residue) although both sides hold steady pressure on the tester after letting pressure sit for a little while. and the car runs really nice except for the rough idle..... your input pleeze
 

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Premium Member
1990 SEC
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4,247 Posts
It is pretty amazing that you have a car that runs properly with a 13% difference in compression between the left and right cylinder banks.

Normal compression should be about 155-160 psi, so 130 is low.

Are really all the cylinders in the left bank (1,2,3 & 4) at 130 psi? Seems kind of odd that a problem would affect all the cylinder equally.
 

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1984 500 sel
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61 Posts
Discussion Starter #4
i don't know if this makes a difference but the car was cold when tested and the comp tool didn't fit (tighten in the plug hole) as well on the pass side either and as a matter of reference because of that, the reading kept being different on that side. so would that make a difference
 
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