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03 Avalanche misfire?

My 03 Chev Avalanche is giving me a P0300 code (multiple or random misfire). With no distributor or individual coil is this something I can fix myself or is it shop time?

You can probably replace the plugs and wires yourself. The plugs are due at 100K. And yes you have CNP (coil near plug) ignition, so you have eight coils.

This came on suddenly. Does this point to a ECM problem?

My guess would be a failing crankshaft position sensor or a faulty connection at the sensor plug.

Most likely not. Change those plugs, see what happens. I certainly wouldn’t wait until 100k to do it.

Find The Main Engine Wiring Harness Ground Wire Where It Attaches With A Nut Or Bolt To A Cylinder Head (I Believe The Right Head) And Make Sure It’s Not Corroded.

This wire grounds the ECM and some have been found to rust / corrode and set misfire DTCs. If it’s not clean then remove it, clean it, and reinstall it.

CSA

I would also stick a fuel pressure gauge on it.