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2003 Envoy SLT AWD 4X4
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Discussion Starter · #1 ·
P0300 code multiple random misfires went off then after a few minutes cylinder 6 went off...I replaced coil pack and plug on 6 but p0300 multiple misfires is still showing up...the ses light dont come on till I'm driving down the road and even then it just flashes on and off......Any ideas? Could it be another plug coil pack or maybe fuel filter throwing the code?? Somebodies gotta know...PLEASE HELP
 

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2003 Chevrolet Trailblazer LT EXT
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453 Posts
After you changed coil and plug on #6 did the engine still run rough ?
The flashing SES light you mention afterwards would indicate that the engine was running very poorly?
If only code coming up is P0300 then the computer is not helping you narrow down which cylinder has the issue. (yet)
You need to start the manual process of one by one ruling out which cylinder is misfiring.
-maybe the new coil did not land correctly on the spark plug?

So many different possibilities
 

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Hubs and I just finished fixing my Mom's 05 Envoy XL 4x4, running rough and chugging like a tractor. Zero power, highway speed is baaaaarely 105kph. Throwing a P0302. Don't even get me started on how she puts up with a vehicle acting like that for nearly a year AND KEEPS DRIVING IT LIKE THAT when we live 90mins away from her and have tools!
After we replaced the VVT solenoid, MAP sensor and spark plugs, the only change was the P0302 switched to a P0300, but it still acted the same. Tested the voltage to the coils, they were fine. We also figured it should be coding coils (P0350-0P365) if it was coils. So we did a 25hr ripdown to replace the timing chain (now I can do it in my sleep thanks to all the info on this site!). Turns out the tensioner was maxed out, the shoes were almost worn through and the chain was on the verge of skipping a tooth!!
Afterwards, it was still throwing a P0300, and chugging like a tractor. So we did the coil check that other guys have suggested, where you unplug each coil while it's running, and if it sounds the same that coil isn't firing. Turns out #1 and #3 weren't likely working all along but the problem was masked by the timing being off.
Anyway, now it purrs like a kitten and it has so much pickup, I took it for a test drive the next day and left tire marks at the intersection.
We're pretty sure that the P0350-P0365 codes weren't actually available in the PCM until AFTER at least 2005, can anyone confirm?
 
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