2019 Camaro ZL1 – P0300 Misfire on Cyl 5 & 8 After Engine and Snout Swap - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

ehabmohamed7676 · 11-10-2025, 05:32 AM

Hey everyone,

I’m hoping to get some insight into an issue I’ve been fighting with my 2019 Camaro ZL1 (manual transmission).

Background:
I recently installed a used engine in the car. After the swap, the upper pulley that came on the engine had been modified to a 2.3” pulley, which caused a P012B – Turbo/Supercharger Inlet Pressure Sensor “A” Circuit Range/Performance code.

Before replacing the snout, I discovered that the MAP sensor on the back of the supercharger (driver’s side) was missing, and the pulley was modified. During that period, I tested the car multiple times — I got P012B and some related codes, but never P0300.

After that, I decided to fix things properly by:

Installing the missing MAP sensor,

Replacing the snout (front part of the supercharger with the pulley) using the one from my original supercharger, and

Replacing the vented hose between the bypass valve and the supercharger (the previous owner seems to have modified it for a louder, more aggressive sound).

Once those were fixed, the P012B code went away, but a new issue started — a P0300 Random/Multiple Cylinder Misfire.

Current Problem:
After driving for a while—especially in 4th or 5th gear—the check engine light flashes briefly, then sometimes stays on or turns off. Scanning shows a P0300 Random/Multiple Cylinder Misfire code.

I brought the car to the dealership, and they kept it for over 20 days but couldn’t find the root cause. Using their scan tools, they confirmed that misfires occur almost exclusively on cylinders #5 and #8, with high misfire counts on those two.

Here’s what has been checked or replaced:

New OEM plug wires

New spark plugs

Coils inspected and confirmed good by the dealer

Compression test shows ~14.5 bar (≈210 psi) on all cylinders

New MAF sensor installed

Air intake: Roto-Fab, used, installed with the engine

Fuel injectors cleaned, with internal filters and O-rings replaced (done by a professional garage, who confirmed all injectors are functioning properly)

Electrical checks: internal resistance measured at each injector and through the connector wiring harness — all readings were consistent and within the same range

If there’s a way to double-check injector performance without removing them, I’d appreciate any suggestions.

Additional notes:

The engine runs fine at idle and under light load.

The issue appears only after driving for a bit, typically under moderate to higher load in 4th or 5th gear.

No abnormal noises or leaks detected.

Has anyone experienced similar misfire behavior after a pulley or snout swap? Could it be related to fueling, vacuum leaks, or something in the tune (given the smaller pulley and airflow changes)?

Any suggestions on what to check next—injectors, vacuum lines, fuel trims, or tuning adjustments—would be really appreciated.

Thanks in advance!

11-10-2025, 05:32 AM	#1
ehabmohamed7676 Drives: Chevy Camaro Zl1 2019 Manual Trans Join Date: Nov 2025 Location: Kuwait Posts: 1	2019 Camaro ZL1 – P0300 Misfire on Cyl 5 & 8 After Engine and Snout Swap Hey everyone, I’m hoping to get some insight into an issue I’ve been fighting with my 2019 Camaro ZL1 (manual transmission). Background: I recently installed a used engine in the car. After the swap, the upper pulley that came on the engine had been modified to a 2.3” pulley, which caused a P012B – Turbo/Supercharger Inlet Pressure Sensor “A” Circuit Range/Performance code. Before replacing the snout, I discovered that the MAP sensor on the back of the supercharger (driver’s side) was missing, and the pulley was modified. During that period, I tested the car multiple times — I got P012B and some related codes, but never P0300. After that, I decided to fix things properly by: Installing the missing MAP sensor, Replacing the snout (front part of the supercharger with the pulley) using the one from my original supercharger, and Replacing the vented hose between the bypass valve and the supercharger (the previous owner seems to have modified it for a louder, more aggressive sound). Once those were fixed, the P012B code went away, but a new issue started — a P0300 Random/Multiple Cylinder Misfire. Current Problem: After driving for a while—especially in 4th or 5th gear—the check engine light flashes briefly, then sometimes stays on or turns off. Scanning shows a P0300 Random/Multiple Cylinder Misfire code. I brought the car to the dealership, and they kept it for over 20 days but couldn’t find the root cause. Using their scan tools, they confirmed that misfires occur almost exclusively on cylinders #5 and #8, with high misfire counts on those two. Here’s what has been checked or replaced: New OEM plug wires New spark plugs Coils inspected and confirmed good by the dealer Compression test shows ~14.5 bar (≈210 psi) on all cylinders New MAF sensor installed Air intake: Roto-Fab, used, installed with the engine Fuel injectors cleaned, with internal filters and O-rings replaced (done by a professional garage, who confirmed all injectors are functioning properly) Electrical checks: internal resistance measured at each injector and through the connector wiring harness — all readings were consistent and within the same range If there’s a way to double-check injector performance without removing them, I’d appreciate any suggestions. Additional notes: The engine runs fine at idle and under light load. The issue appears only after driving for a bit, typically under moderate to higher load in 4th or 5th gear. No abnormal noises or leaks detected. Has anyone experienced similar misfire behavior after a pulley or snout swap? Could it be related to fueling, vacuum leaks, or something in the tune (given the smaller pulley and airflow changes)? Any suggestions on what to check next—injectors, vacuum lines, fuel trims, or tuning adjustments—would be really appreciated. Thanks in advance!