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

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?

2 Replies

MHPAUTOS

MECHANIC
31,937 POSTS

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

JRMINES7

MEMBER
2 POSTS

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