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My 03 Sierra with 5.3 has a check engine lite. Scanning it revealed a code P0307 cylinder 7 misfire. I changed the coil and the code changed to a P0300 multi cylinder misfire. After a few resets it reverted back to P0307. New plugs and wires did not help. (at 96K mile they were about due anyhow) Swapping coils between 1& 7 caused the code to temporarily go to P0300 then back to P0307.

Other symptoms are rough idle, stumble on acceleration. Decrease in gas mileage.
Scan tool also says:
"CAT not ready"
"EVAP not ready"
Don't know if they mean anything or not.

You guys have any experience with this stuff?
 

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Hi,

I found this service bulletin, maybe this will help!


ID: 10009666
Bulletin #: 3055
Replacement #:

Bulletin Date: 20040101
Date Added: 20041014

Failure Code: 061000 ENGINE AND ENGINE COOLING:ENGINE

Make: CHEVROLET
Model: TAHOE
Year: 2005

Summary:
SERVICE ENGINE SOON LIGHT WITH A P0300 MISFIRE DUE TO MISFIRES MAINLY ON CYLINDER 7. *TT
 
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