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Code was a P0300 multiple cylinder misfire, but did not specify which cylinder. I monitored misfire occurrences on scanner while driving and all cylinders on bank 1 (cyl 1,3,5,7) would misfire when the condition happened. Went to auto parts store and got 8 new coil packs ( Standard Auto UF743) and 8 new plugs (AC Delco 12622441).
So for well over a year I have been fighting a periodic cylinder 7 misfire. The light will flash under a load or accelerating at highway speeds. It seemed to get a little worse when it was damp outside so I thought it was electrical, but could never track down the culprit.
The other day I spoke with a head mechanic "friend" of mine. I explained all that I have done and what the symptoms are, mostly it has been a rough idle / misfire, P0300, but the misfire count is only on cylinder 7. It starts fine, accelerates and drives fine. He said then that it really sounds like an injector issue.
I cammed my 5.3 with Texas speed stage 1 32% fuel lobe afm delete and procharged. I’m getting a p0300 random cylinder misfire code after driving for about 40 minutes. I can delete the cel but it comes back after an hour or so of driving. I checked my obd 2 scanner tool and the misfires build slowly but 3 and 7 build faster than others.
I have been chasing a multiple cylinder misfire on my truck for months. I have replaced my throttle body gasket, Intake manifold gasket, spark plugs, spark plug wires, purge solenoid, vapor canister, rear vapor canister vent hose, o2 sensors, map sensor, gas cap, and fuel pump. I am thinking about also replacing both harnesses for the coil packs.
Figured, I'd do the coil pack just to completely rule out intermittent spark. Nope, still misfired... but only when cold and only when getting it up around 2500 RPM. The crazy part is, I NEVER feel it. I just see a flashing SES light. If it's warm, there's never a problem. Thought, AHHH, this has gotta be the famous Chevy Silverado gaskets.
2007 Silverado 5.3. Has a misfire on cylinder 4 and also smells rich. I would assume it is something with the spark. I have already replaced all spark plugs, spark plug wires, and coil pack. It also shifts hard into second. Along with the misfire the Crankshaft position sensor needs to be relearned (getting done very soon).
The check engine light came on throwing code p0305 which is a misfire in cylinder 5. So we replaced plugs, wires and coils on all 8 Cyl. Now it will run fibne for a few days then start to misfire again and the following service messages popped up: Stabilitrak off, traction control off, service stabilitrack, service traction control.
Sorry for my spelling * hung. The po300 is a hard code to diagnoise. I work at a chevy dealership, I see lots of Chevy 5.3's with p0300's. Also there was a bulletin a whilr back to clean the ground going to the block, That was found to cause a po300 as well. But I would look at a cylinder leakage test. It will tell you if a vavle is hung open.
First time here, and very excited to find the Forum. Hopefully the array of talent can help me narrow down a problem. I have a 2017 Silverado 1500 LTZ Z71, 5.3L engine. She has 115,000 miles on her, and two weeks ago, I had a P0420 Code and was told I had to replace my Catalytic Converters. I had the repairs done on Saturday (6/27/20).