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Misfire

Tiny
GREG C.
  • MEMBER
  • 1998 GMC SIERRA
  • V8
  • 4WD
  • AUTOMATIC
  • 130,000 MILES
1998 GMC Sierra SLE 4x4
5.7 Vortec 4spd auto

Has P0300 DTC with misfires in #2 and #8 cylinders. All sensors seem to be operating in normal paramters and no apparent vacuum leaks. Plugs/Dist cap/rotor button new.

EGR readings from scanner stay at 0% from idle thru max. Rpm
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Saturday, July 23rd, 2011 AT 8:31 PM

3 Replies

Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
Has cylinder compression been checked? Injectors operating? Spark at plugs? Did 2-8 show up in miss fire history?
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Saturday, July 23rd, 2011 AT 8:44 PM
Tiny
GREG C.
  • MEMBER
  • 2 POSTS
Spark is present at plugs, Miss fire started during normal operation at 50 mph, no prior history. Truck has Sequential Port Injection, don't think I can physically check injectors with out pulling intake. Did coomplete test with Tech 2 scanner by disabling individual injectors. Disabling of #2 and #8 made no difference in running condition, all other did effect running. Checked manifold, vacuum lines and components attached to upper manifold for vacuum leaks by spraying with cleaner with no effect.
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Saturday, July 23rd, 2011 AT 8:57 PM
Tiny
DOCFIXIT
  • MECHANIC
  • 18,828 POSTS
You have answer to problem need to remove upper manifold and check injectors 2-8
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-1
Sunday, July 24th, 2011 AT 7:28 PM

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