2.8 shakes when at idle compression is

stevo28 · 11-16-2011, 03:16 PM

I have just boughten my very first Audi . 1999 A6 Quatro with 30V 2.8. problem is shakes when at idle, give it a little gas --goes away and seems to run well, however this bothered me so I did a compression test and have found right side 3 cylinders have 75 psi each and left side has 125 ea. . So now I think my shakew is a unbalanced motor. exhuast smells a little funky almost gasey. plugs are darker on right than left but am sure less cylinder pressure is culprit. I have somewhat ruled out head gasket since it is all 3 cylinders on one side . but would a cracked head do this. guy i bought from says it looses may-be a cup of water a month oil smells good... Any Ideas? Is there a decompresion valve or something of that nature due to engine light on ?

Prospeeder · 11-25-2011, 07:01 AM

Wow, try putting a small amount of oil in those 3 low cylinders and see if it jumps up to normal. If it doesnt make much difference, the Rings are good. If it does make a big difference, the rings are bad. You then have burnt, slightly bent valves as a possisblity. Also CAM timing off will scew compression numbers. I would especially suspect cam timing seeing as that entire bank is off evenly. So start there. Get the proper timing belt tools, put it at the timing mark on the crank, and see if the bar will install into place. If it wont, timing is off. Also the chain tensioners will go bad, or the chain will relax and make cam timing off. Also i have seen people run engine out or nearly out of oil and cause the cams to drag in thier bearings and "twist" the end, making timing off. So theres some stuff to check for you.

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11-25-2011, 07:01 AM	#2
Prospeeder AudiWorld Senior Member Garage is empty, add now Join Date: Aug 2011 Posts: 837	Wow, try putting a small amount of oil in those 3 low cylinders and see if it jumps up to normal. If it doesnt make much difference, the Rings are good. If it does make a big difference, the rings are bad. You then have burnt, slightly bent valves as a possisblity. Also CAM timing off will scew compression numbers. I would especially suspect cam timing seeing as that entire bank is off evenly. So start there. Get the proper timing belt tools, put it at the timing mark on the crank, and see if the bar will install into place. If it wont, timing is off. Also the chain tensioners will go bad, or the chain will relax and make cam timing off. Also i have seen people run engine out or nearly out of oil and cause the cams to drag in thier bearings and "twist" the end, making timing off. So theres some stuff to check for you.