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Discussion Starter · #1 ·
I have a 2003 Suburban Frankenstein yes the year that Chevy decided to use parts from everything I have changed just about everything on the truck yet I still showing random misfire code po300 my HP scanner shows a misfire in cylinder 2 and 6 only I've run out of ideas can you help
 

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Have you tried a compression check on those cylinders?
 

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Discussion Starter · #3 ·
Yes compression was around 1:25 to 1:30 I'll go on cylinder number to it seemed to be a little erratic but if I let it crank maybe 7-8 10 times it showed 130 final as soon as you accelerate over a thousand RPM it runs like a champ it runs like a champ I can manipulate the timing and air fuel with my HP tuner and it'll run beautiful turn off the ignition go have a beer when I come back it reverts back to its old rough idle I can't figure it out I think something with timing
 

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Let's get rid of the other thread.

I assume a 5.3.

Maybe you need a crankshaft position relearn.
 

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As mentioned above you may need a crankshaft position relearn. Especially since you "changed everything" on GM vehicles if you have a bad crankshaft position sensor and you replace it with a new one without doing a re-learn it will still run poorly like it has the original bad one in it.
 
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