Hello,

car began to run rough & I thought it was another coil...been through 3 so far....luckily not #3 yet...Lol ....however, I do have low compression on #5, about 30 psi. injector good, coil good, plug good. I'm thinking I have a bad valve or something of the sort...

Anyone ever have this? I want to sell this car..it is in great shape other than it's current problem...bought new truck & my Infiniti started screwing up 4 weeks later...

Any help is much appreciated..

Sam

 

Low compression in one cylinder usually indicates a bad exhaust valve.

Low compression in two adjacent cylinders typically means you have a bad head gasket.

Low compression in all cylinders would tell you the rings and cylinders are worn and the engine needs to be overhauled.

 

Low compression itself doesn't necessarily mean a bad valve. In fact, a sudden "bad" valve by itself out of the blue on an otherwise up-to-that-point good running engine would be somewhat unlikely. I would almost always suspect a ring issue over valve issues on a good running car.

You should drop a little oil down the spark plug hole and re-test right after adding the oil. If the compression raises on the re-test then you have bad rings (or something else ring-related - scored cylinder wall/ring land damage/etc). If the compression does NOT raise THEN you can fairly well suspect a valve issue.

 

sounds like rings

 

sounds like money...Lol


I want to sell it. this sucks....been a great car... did the compression thing 2-3 weeks after I buy a new ride... was about to list it for sale!!

Thanks folks..I'l try the oil thing in the hole...I have heard of that one... I was hoping for a stuck valve & I have put the Rilone (oil detergent) in there to try to free it up....mechanic in a can!

but the problem is it goes into safe mode because of the miss causing very rich exhaust....so I can't run it around to get the RisLone mixed around...

 

Anyone know how much a valve job on one of these things goes for?

 

Can you borrow a leakdown tester? You need to set the cylinder to TDC on the compression stroke. Then do the leakdown test. You then can hear where the escaping air is going and that'll indicate where the problem is.