Misfire on PCM H5

[nathandantzler]

Cylinder 1 Misfire on PCM H5DI 5.3L — DTC 1311 & DTC 301




Hey everyone. I have a 2018 Nautique G21 with the PCM H5DI 5.3L direct injection engine and I'm chasing down a cylinder 1 misfire. Looking for anyone who's dealt with something similar.




THE ISSUE:

Engine runs fine at idle and low RPM, but after about 5 minutes of running under load at higher RPM, I get two fault codes:

- DTC 1311 — Cylinder 1 Misfire Detected

- DTC 301 — Cylinder 1 Emissions Catalyst Damaging Misfire




The fault log shows this code has occurred 127 times, so it's clearly been happening for a while.




WHAT I'VE ALREADY CHECKED:

- Replaced the spark plug on cylinder 1 — plug looked clean and dry, no fouling or oil

- Inspected and cleaned the spark plug wire with contact cleaner

- Plug well looked normal




BACKGROUND:
I recently bought this boat, knowing that had an issue with the NSS, which turned out to be the LINC panoray set to the wrong boat model. (I suspect the screen had been replaced before)
I also previously had DTCs for high side injector faults on multiple cylinders, which turned out to be caused by corrosion on a single pin on the ECM connector. Cleaned it up and that resolved those codes. Not sure if this current misfire is related or not — all the other ECM pins look completely clean, so it may be a separate issue.




MY CURRENT THEORY:

Given that it only misfires under load at higher RPM and runs fine at idle, I'm leaning toward either a weakening coil pack that can't keep up at higher firing frequency, or corrosion in the wiring between the ECM and the coil pack on cylinder 1. The boat has a history of water/storm damage so corrosion throughout the electrical system is a known issue.




Has anyone experienced this specific misfire pattern on the H5DI? Any tips on testing the coil pack or the signal wire without pulling the intake manifold would be greatly appreciated.




Thanks

[JayG80]

I’d swap the plug and wire with another cylinder and see if the misfire follows. Do you have the diagnostic manual?

https://skidim.com/gcp-4g-diagnostic-manual/

[core-rider]

You’ve already changed the plug so no real reason to swap it. Swap the coil and plug wire to another cylinder and see if the issue follows to the new cylinder. That will easily rule out those parts or not. If no change, then could be wiring going to the coil or maybe an issue with the injector. I’m not real familiar with the DI stuff so diagnostics for it is out of my pay grade.