'92 cylinder compression failure
'92 cylinder compression failure
had a rough idle on my '92 Q, tested all the injectors (ok) and performed a compression test dry and wet. cylinder number 2 was 105 psi vs 175-180 for all the others. no difference wet or dry, what would be the likely culprit? i tried to do a cylinder leakdown test but could not determine where the leak was coming from.:help
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Almost never a blown head gasket [due to design]. Pull the valve cover and make sure all the cam followers on #2 are still attached.
Do a leak down test in 2 positions top dead center and 45-90 degrees down......the exhaust valve begins to open at 120 degrees after TDC and maximum BMEP occurs at 15-17 degrees after TDC so the perfect place to check it.
To find where use a stethoscope and listen to the throttle body input [intake valve] or exhaust at muffler [exhaust valve], or place over the oil fill port [luckily that at #2] rings into crank case.
Wierd all the others are correct and 105 on that one.
You never said how many miles?
Do a leak down test in 2 positions top dead center and 45-90 degrees down......the exhaust valve begins to open at 120 degrees after TDC and maximum BMEP occurs at 15-17 degrees after TDC so the perfect place to check it.
To find where use a stethoscope and listen to the throttle body input [intake valve] or exhaust at muffler [exhaust valve], or place over the oil fill port [luckily that at #2] rings into crank case.
Wierd all the others are correct and 105 on that one.
You never said how many miles?
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240sleeper
- Posts: 65
- Joined: Fri Aug 23, 2002 11:21 pm
A leakdown test tool is required, in addition to a compressed air supply. The tool is basically 2 pressure guages with a hose that threads into the spark plug hole. It hooks up to the air supply and measures the supply pressure, and then you compare it to the cylinder pressure. A healthy cylinder with the valves seated should be within a certain percentage of the supply pressure. Not sure how close your engine should be, but probably less than 10% different.