Engine running rough, code PO300?

1REDNCK

MEMBER
2004 CHEVROLET SILVERADO
6.0L
V8
4WD
AUTOMATIC
225,000 MILES

I have the truck listed above Silverado 2500hd with 6.0 gap engine. I was driving home one-night the next day woke up started my truck and it was running really rough. Hooked my code reader up it said po300 which is misfire, so I replaced all plugs and wires problem still there replaced all coil packs. Still misfire checked codes again this time it came up with a code for the ECM as well as misfire, so I ordered an ECM and put it in and still running rough checked codes, code po300 and light still flashing still says misfire. Truck stalls when coming to a stop and still getting could the ECM I got be bad?

Friday, May 12th, 2023 AT 12:12 PM

1 Reply

JACOBANDNICKOLAS

MECHANIC
110,114 POSTS

Hi,

A p0300 is a random misfire. If the check engine light is flashing, that is when the misfires are occurring. Keep in mind, there are many things that can cause this code to set and doesn't mean the ECM is faulty. For example, a fuel pressure issue or engine vacuum leak can cause it.

What code did you get that is related to the ECM?

Also, take a look through this link and let me know if it helps:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Let me know.

Joe

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Friday, May 12th, 2023 AT 9:44 PM