Craig Gillard

Asked by Jun 05, 2016 at 02:53 AM about the 2004 Chevrolet Silverado 1500 Z71 Ext Cab Short Bed 4WD

Question type: Maintenance & Repair

I have a problem. My 2004 Chevy Silverado will
idle fine for about 30 seconds then all the sudden
my 6th cylinder only will start to misfire. I have
changed my Mass Air Flow sensor, switched out
the coil, switched out the spark plug and wire,
switched out fuel injectors, cleaned out fuel rails,
checked for fuel pressure (it's fine), and even
changed out my downstream O2 sensor in Bank 2.
If I turn the truck off and start it, it will idle just fine
and then again after about 30 seconds of idling it
will start to misfire in only the 6th cylinder. I need
some advice. Any and all help is appreciated!

6 Answers

Tom Demyan

What was the condition of the spark plug on cylinder #6? If you replaced the ignition and fuel injectors, the next step would be to do a leak down and cylinder pressure test to see if that #6 cylinder is lower than the other cylinders. Meaning a faulty head gasket or a valve problem. Good luck.


Should do a compression test on the cylinder, should be around 150 psi. and no lower than 120.

Bob Beaman

I agree with Rowefast, you either have a compression problem or an intake manifold leak at #6.

Craig Gillard

Spark plug in the 6th cylinder was just fine. It didn't seem wet like it was getting flooded or anything. We checked the compression in the 6th cylinder that misfires and compression was just fine.

Craig Gillard

Also if I put it in gear right after I start it, it won't misfire but it still seems to run sluggish. Thanks again for yalls help.


Sounds like you now have to dig deeper into the problem. Ideas I have at this time would be to check the power running to the coil, inspect the wire, check the voltage once she starts to miss-fire, make sure the ground are good. Also you may want to do a fuel bleed down test by hooking up a fuel pressure gauge to the Schrader valve up located up on the intake. Build up fuel pressure by cycling the key on, off, until fuel pressure builds up, should be 56 to 63 lbs. Turn the key off and watch the gauge, it should not drop in pressure more than 5 lbs. in 3 minutes. If it does, this indicates a leaky injector, line, or fuel regulator.

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