# 99 Yukon Random Misfire



## zach1926284 (Nov 17, 2013)

So just re did the top end and adjusted the valves twice, still getting codes for random misfire on cyl 6, repaved the injectors and started getting this problem has new plugs, wires abd cap n rotor and I'm stumped as to wat could be causing this problem any ideas would be appreciated


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## toolaholic (Jul 31, 2011)

Cracked porcelain on spark plug. Many yrs (1992) ago I had a 85 t bird w/ a 302v8. I changed plugs myself. Car would miss at low speeds. Dealer charged me $500( new egr valve etc) to fix. Still missed. Turned out to be a hairline crack on spark plug.


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## ddawg16 (Aug 15, 2011)

...pull the fuel pump relay....

Crank the engine over for about 30 seconds..

Pull the plug....look at #6....does it have any moisture on it? If so...leaky head gasket.


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## Hardway (Dec 28, 2011)

Did you use OEM AC Delco parts?


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## zach1926284 (Nov 17, 2013)

Used felpro higher end gaskets, ac Delco plugs, ended up being one of the new injectors not sitting correctly and corrected itself, drove it last night after my wife had been driving for a few days and no longer misses at any rpm so that's honestly the only thing I can think of that could've been the problem, New design doesn't have the oem clips from 99, it was changed by gm in 00 or 01 according to service notes from gm global connect


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## ukrkoz (Dec 31, 2010)

You can adjust valves on Yukon V8-s? Don't they have hydraulic lifters?


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## Windows on Wash (Aug 30, 2011)

ukrkoz said:


> You can adjust valves on Yukon V8-s? Don't they have hydraulic lifters?


+1

That is a bit scary to start with.


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## zach1926284 (Nov 17, 2013)

Not the lifters as its not a consistent misfire


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## ukrkoz (Dec 31, 2010)

Zach, you missed my question. I have never heard of valve adjustments on GM V8s for those years, as they have hydraulic lifters. I was curious, how did you adjust the valves then. Your OP said so.

_adjusted the valves twice_


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## Windows on Wash (Aug 30, 2011)

+1

That was my point as well. Most GM Rocker assemblies are just bolt down until snug these days or spin the pushrod until you feel drag and 1/4 - 1/2 turn beyond there.


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