Will a bad tune cause random misfires (P0300)?

[bsteff]

I'm chasing a p0300 code and I am curious as to whether the tune itself could be causing it. I replaced the PCM and on the stock tune it was running rich, had misfires on cylinders 2 and 7 at startup but then they cycled out. Had the tune flashed back in and now it runs like shit. Misfires on cylinder 8 constantly and 2 and 7 at idle (when it will idle). Should I go to a different tuner or continue to chase the misfires? I have a new throttle body and coil packs on order, sprayed starting fluid to check for vacuum leaks but couldn't really tell because of the idling issue. Any thoughts/inputs?

[cornerman]

A second opinion is always a good idea
And sometimes a third!
Sounds mechanical to me, valve issue maybe

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[79Firebird_99TA]

I'm in the same boat as you. It's a new build. The tuner states that he's not done. I hope it's not mechanical.... but it's on him.

[SMWS6TA]

Check the plugs and wires. Plugs crack. Also check the wire harness for the coils to insure no crack or broken wires.

Common causes for P0300

• Faulty or worn spark plugs
• Faulty spark plug wires or coils
• Distributor failure (Carb only)
• Faulty fuel injector
• Vacuum leak
• Low fuel pressure
• Camshaft sensor defective
• Crankshaft sensor defective
• Engine timing off
• Leaking head gasket
• Low engine compression
• Poor quality fuel

All of these you can do and not have a mechanic charge you for.


Now regarding the ecm and tuning. This is a difficult answer. Meaning it could be a bad tune, ecm or tuner.

Do you have the correct ecm? There are different years of ecm's 98, 99-00, 01-02. 99-00 and 01-02 have the same pin out for the harness for the ecm while 98's have a much older and different pin out for the ecm. You can get a 99-00 ecm and have the software upgraded to 01-02.

How much tuning experience does the tuner have with LS1's?

You need to rule out the mechanical issues first, otherwise your tuner is chasing ghosts. For example when tuning mine after my 403 build I would have an idle issue all over the place but once I got above 2k rpm it would smooth out and have zero issues. After going thru 2 sessions of tuning and a different tuner, the 2nd tuner figure out that my map sensor was cutting out. I pulled my intake off to replace and relocate it and found that the seal on the FAST intake was torn and causing a 8" vacuum leak that would seal once I got into the pedal. Fixed those two issues and bam smooth idle and was able to finish tuning.

[thenexttech]

Yes, a bad tune can cause random misfires (P0300). A misfire can occur when the engine is not firing the correct amount of fuel or ignition timing is off, which can be caused by a poor tune.

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[Whamhammer]

First thing I would do, is move ignition coils to different cylinders, and see if the misfire codes move with them.