#5 and #6 cylinder misfire during idle, but goes away when engine is revved. Engine is 4.2L I6.

Tiny
JRMINES7
  • MEMBER
  • 2005 CHEVROLET TRAILBLAZER
  • 13,500 MILES
Check engine lite came on at 98K. Replaced all 6 spark plugs by a shop.
Mechanic says that #6 injector is 'lazy'. Does not inject proper amount of fuel during idle but ok at higher rpm(1,500). Since I do alot of highway driving, I just let it go. Now at 120K, I'm noticing #6 getting
more misfire when accelerating. Had shop replace #6 injector. But now the mechanic says their diagnostic equipment says #5, and #6 is having misfire only at idle speed, but when revved up, misfire goes away. He swapped coils on #1, and #2 to #5, and #6 with same results. Mechanic says could be a blown head gasket. My thoughts is, if it is a compression problem, then why the misfire goes away at when engine is revved about 1500rpm. I just want a second opinion on this. Thanks for your help?
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Sunday, January 15th, 2012 AT 8:37 AM

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Tiny
MHPAUTOS
  • EXPERT
Get a head check done, this is a simple chemical test to check for Co in the cooling system, also a leak down test will show up a gasket problem, get either or both of these tests done first.
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Sunday, January 15th, 2012 AT 1:57 PM
Tiny
JRMINES7
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If its a bad head gasket, the hoses should be a bit hard to squeeze due to compression leaking into the cooling system. I'm not loosing any coolant at this time.O
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Sunday, January 15th, 2012 AT 5:05 PM

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