unexplained mis
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unexplained mis
Hi, I have a 1999 5.4 L F150, and am having an unexplained misfire at low revs.
The vehicle developed a service engine light and was serviced using only genuine Ford parts from the local dealer. The light was reset , but started to show again and the low level misfire again started. A diagnostic check was done by a local repair shop who advised that the Co sensor was defective. This was replaced again using a genuine part. The light went away and reappeared the followinfg morning along with the......LOW level mis...., two diagnostic checks later and two coil packs later the shop informed us that a burned valve was the the culprit.
The heads were removed and valves reground , two new valves replaced although we could find no evidence of burning , the engine was re asembled and vacuum leak checks done , the low level mis was still there but intermittent. The vehicle then had the injectors cleaned and this problem although less was still there.
A drive home the night brought out a serious misfire. The dealer did a diagnostic and first said that 4 coil packs were neede, then said that the whole of the left hand bank was reading below 80psi, and that the valves needed to be properly seated.....which does not make senes as it would have been possible to have one pr two cylinders with improper seating but the likelihood of being all on one side is negligible and unlikely. A mechanical compression check of all cylinders showed none below 170psi. The low level misfire still persists, drop the tank, check for dirt in the line clean the pump strainer, check fuel rail pressure, 32psi, disconect the vacuum line pressure goes to 40psi, and still the low level misfire continues...will someone please help???? can anyone give clues? I need to get rid of the LOW LEVEL MIS!!!!!!
The vehicle developed a service engine light and was serviced using only genuine Ford parts from the local dealer. The light was reset , but started to show again and the low level misfire again started. A diagnostic check was done by a local repair shop who advised that the Co sensor was defective. This was replaced again using a genuine part. The light went away and reappeared the followinfg morning along with the......LOW level mis...., two diagnostic checks later and two coil packs later the shop informed us that a burned valve was the the culprit.
The heads were removed and valves reground , two new valves replaced although we could find no evidence of burning , the engine was re asembled and vacuum leak checks done , the low level mis was still there but intermittent. The vehicle then had the injectors cleaned and this problem although less was still there.
A drive home the night brought out a serious misfire. The dealer did a diagnostic and first said that 4 coil packs were neede, then said that the whole of the left hand bank was reading below 80psi, and that the valves needed to be properly seated.....which does not make senes as it would have been possible to have one pr two cylinders with improper seating but the likelihood of being all on one side is negligible and unlikely. A mechanical compression check of all cylinders showed none below 170psi. The low level misfire still persists, drop the tank, check for dirt in the line clean the pump strainer, check fuel rail pressure, 32psi, disconect the vacuum line pressure goes to 40psi, and still the low level misfire continues...will someone please help???? can anyone give clues? I need to get rid of the LOW LEVEL MIS!!!!!!
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Joined: Dec 2001
Posts: 22,436
Likes: 17
From: Louisville,Ky.
Welcome tot FTE 
I wonder if ther is a wiring problem to the bad bank of COP's. If the shop had washed the engine after the repair, water could have gotten into the spark plug pockets and caused a short which could burn up the COP's (Coil On Plug).
If all of the cylinders have close to the same of the compression, then I would doubt that you have a valve problem.
I wonder if ther is a wiring problem to the bad bank of COP's. If the shop had washed the engine after the repair, water could have gotten into the spark plug pockets and caused a short which could burn up the COP's (Coil On Plug).
If all of the cylinders have close to the same of the compression, then I would doubt that you have a valve problem.
