1999 GMC Sierra

1999 GMC SIERRA
193,055 MILES • V8 • 2WD • AUTOMATIC
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DARRYLBENALLY
  • MEMBER
  • 1 POST
my 1999 GMC sierra 5.3l 323cid V8 diagnostic always showing misfire on cyl. #4 i change spark plugs , wires , ign. coil, fuel filter, mass air sensor, and vehical has erratic idle than good idle and runs all day and looses power and popping in engine starts
Aug 30, 2009 at 1:39 PM
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RASMATAZ
  • ✓Experienced Mechanic
  • 75,988 POSTS
Check compression and injector for the no.4

Engine 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
Aug 30, 2009 at 5:41 PM
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