Mechanics

CHEVY ROUGH IDLE AND MISFIRE

1998 Chevrolet Silverado

Engine Performance problem
1998 Chevy Silverado V8 Four Wheel Drive Automatic 146000 miles

I have changed dist cap, rotor, sparkplugs(@ 100,000), wires, fuel filter, and cleaned maf sensor. I didn't have codes a first but, then service engine light came on and code said cylinder 5 misfire. I pulled the sparkplug and the electrode was built up with black crusty gunk on one side and white and clean on other side. Plug in cylinder 3 was also built up. I changed the plug (5) and added seafoam cleaner to gas. Local Autozone guys said it could be a clogged injector, bad plug, or I may need to change injector spider. I have run a tank of gas with seafoam and Idle seems to be better at times but not always. It is worse when cold. Acceleration was rough but seems smoother after I cleaned MAF sensor Is there anything I missed? Thanks, Mike
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Miketay
May 13, 2009.




Misfire @ 5 could be the plug/compresssion/injector on that cylinder. Try cleaning out the idle air control valve

Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
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Tiny
Rasmataz
May 14, 2009.
I found the problem. After checking all sensors. I decided it had to be the intake or headgasket. On teardown I found the plastic intake gasket I replaced at 100,000 miles had warped into a slight arc. After removing the gasket, I could see the o-ring seal had dropped below the #3 & #5 ports which created a vacuum leak and sucked oil into the cylinders. I replaced the intake gaskets with metal gaskets and reassembled. She runs great and does not use any oil. Problem Solved! Thanks for the help! Mike

Tiny
Miketay
Aug 5, 2009.

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