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Low compression on one cylinder and rough idle

Tiny
CHARLES
  • MEMBER
  • 1984 FORD F-150
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 10,000 MILES
I had a rebuild engine installed 10,000 miles ago and it recently started running rough at low rpm. I had it checked and it has low compression on one cylinder. The mechanic squirted oil in the cylinder and compression came up some. It uses no oil, does not smoke and has no blow by coming out of filler tube. Could this be a head gasket leaking? Cannot believe it could be the rings.
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Wednesday, October 18th, 2017 AT 8:11 AM

1 Reply

Tiny
MHPAUTOS
  • MECHANIC
  • 31,937 POSTS
It will be a failed compression ring, the oil has sealed the ring for the compression test, if it was okay and the problem was top end you would not get an increase in compression readings with a wet test. Just how much did the compression come up is the next question. I would be more inclined to do a leak down test, this will give you a better understanding as to where any compression leak is and how bad it it is.
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Wednesday, October 18th, 2017 AT 7:30 PM

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