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Old 10-28-2009, 06:08 PM
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04 5.3 silverado misfire

I have had a problem with my 04 silverado 5.3 not flexfuel. I have had a constant misfire on cyl 3. it idles rough enough to through a code. I swaped coils from a different cyl the mis did not follow the coil. So i replaced the injector. This did not help, so I did as I should have from the begining and did a compression and leak-down test. All cyl except 3 had 140-148 psi cyl had 90 consistantly. The leak down test I couldn't hear any abnormal air flow the the exhaust, intake, pvc, or crankcase the cooling system however did sound bubbly with air in the cyl. Bingo I thought i figured it out. so I replaced the head gaskets. When Everything was apart the heads were clean, The was no slugde or varnish. The valves all look great rockers in great shape ect. Got it all back together, and its still missing on cyl 3. Is it possible that a valve on cyl 3 is collapsed and not lifting all the way causeing the miss? If so who makes quality replacement lifters, and should I replace the pushrods and rockers as well? Is it a big deal if i only replace one cyl bank? Thank you for any insight you my have.

Kris Ferguson

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Old 10-28-2009, 06:52 PM
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Quote:
Originally Posted by 10Tonhammer
I have had a problem with my 04 silverado 5.3 not flexfuel. I have had a constant misfire on cyl 3. it idles rough enough to through a code. I swaped coils from a different cyl the mis did not follow the coil. So i replaced the injector. This did not help, so I did as I should have from the begining and did a compression and leak-down test. All cyl except 3 had 140-148 psi cyl had 90 consistantly. The leak down test I couldn't hear any abnormal air flow the the exhaust, intake, pvc, or crankcase the cooling system however did sound bubbly with air in the cyl. Bingo I thought i figured it out. so I replaced the head gaskets. When Everything was apart the heads were clean, The was no slugde or varnish. The valves all look great rockers in great shape ect. Got it all back together, and its still missing on cyl 3. Is it possible that a valve on cyl 3 is collapsed and not lifting all the way causeing the miss? If so who makes quality replacement lifters, and should I replace the pushrods and rockers as well? Is it a big deal if i only replace one cyl bank? Thank you for any insight you my have.


Kris Ferguson
Yes, it is possible that the lifter is faulty or the cam has a "wiped" lobe. I would remove the valve cover, start the truck and watch the rocker arms on #3 cyl. to see if they are operating like the rest.
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Old 10-28-2009, 06:56 PM
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It could be a restriction in the exhaust system. Try dropping the Y-pipe and running it. Let me know what you find. Good luck. Also make sure you clean the MAF sensor. Another potential cause.

Kurt
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Old 10-28-2009, 11:51 PM
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have you checked your electrical end of the system.Chevy used such a small gauge wire on the system.try pulling on your wires individually and you may find a break inside the plastic that will not show up until pulled on.usually where they enter a holder or clip.check your wires going to the coil with that method also.there is a single ground wire at the back of the engine on the passenger side and one at the front side of the drivers side that have been very problematic.
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