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Discussion Starter · #1 ·
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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