2001 Ford F-150 Misfire

Tiny
SRWILKE
  • MEMBER
  • 2001 FORD F-150
  • V8
  • 2WD
  • AUTOMATIC
  • 165,000 MILES
I have a 2001 Ford F-150 pickup 4.9L and it has a miss on #7 cylinder. We have checked and replace the coil pack, plug and injector and it still misses. Compression is at 30 psi but holds compression under compressed air with valves closed. Valves would have to be in good shape. What other possible causes could we check. Everything seems to be working properly. Could it be possibly the intake somehow?
Sunday, December 14th, 2008 AT 12:07 PM

2 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Compression is at 30 psi. What cylinder?

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
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Sunday, December 14th, 2008 AT 12:16 PM
Tiny
SRWILKE
  • MEMBER
  • 1 POST
Everything seems to check out ok. Its the number 4 cylinder. Compression checks out at 30 psi while it is running but holds compression while air hose is installed with valves closed. Injector has been replaced and swapped with another cylinder. Still same problem. It has to be a compression problem but cam is ok. Valves, springs, lifter, rocker. Everything seems ok.
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Sunday, December 14th, 2008 AT 6:32 PM

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