QuestionThank you for the input, Dave. Is there any chance it could be the piston rings? The mechanic used a scope to look into the cylinder and saw no scarring to indicate a broken ring though. Is it possible the ring is gunked up and only operating part of the time? Someone suggested a defective lifter. Any thoughts?
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Followup To
Question -
I have a 1987 944S Porsche. The problem is that ocassionally the number 1 cylinder loses all compression... 0 lbs. Then, after 7 or 8 minutes of driving, the compression returns to normal. The car has 115,000 miles on it and has been well cared for as I have owned it for 14 years.Any suggestions?
Answer -
John,
You have called it loss of compression, which would imply the valves are not opening and closing properly for your 7-8 minute time period...yet they rerturn to normal afterwards. Since the valves are completely mechanical, it seems they would either be working properly... or not, rather than intermittently.
An electrical problem, on the other hand, is its happiest when it can be intermittent and totally frustrating. I'm going to stick my neck out and say the problem is the fuel injector...and its wiring connections. There are ways for the home mechanic to test this, and it's described very well in 'Porsche 944 Automotive Repair Manual', published by Haynes. It's Haynes' product number 1027 or 9U4-1027. Your favorite auto parts store will have it, or can order it. I've also seen them new and used very reasonably priced on sites like bookfinder.com and others.
The auto parts store will likely want up to $20, but whatever price you pay you'll get all your money back and more in value...and knowledge about your little beauty.
Dave
AnswerWell...
I didn't know you'd already had a professional mechanic eyeballing your cylinder walls...that must be quite a view. (Only a greasemonkey like me could appreciate that!)
As for gunk on the rings...it's hard to imagine a car with so little mileage (comparatively) and that's been well cared for and that has passed periodic smog tests would have the kind of gunk you're imagining. As for the defective lifter, you don't have lifters. Your cam lobes push the valves directly, no pushrods, no lifters, nothing to be defective.
Did your mechanic give you any other possibilities? I have to assume he was headed in the lost compression path to be looking at your cylinder walls. There must be some fact I'm missing for me to be so far off the mark as to discount any mechanical fault until the electrics are checked first.
Dave
