Misfire issues!!!

[JoeSpear]

2016 Scarab 255 HO. Pesky misfire issue that I can’t seem to remedy. Faulting P0300 and P0301 on starboard engine…. Runs fairly good up until 5k rpm (still Misfiring but not really impactful to performance) beyond 5k rpm it misfires significantly and cant keep the rpm timed up with port side motor. If I hammer down, the rpm sometimes pops up and down dramatically. I’ve done the following with no remedy…
- new plugs. Not fixed. Even swapped plugs with port side, still misfiring.
- swapped coils with port side, no change.
- removed and cleaned injectors, not fixed.
- swapped injectors with port engine, still not working.
- replaced 02 sensors, not fixed.

Planning next…. Swapping Ecu with port engine, swapping wiring harness with port engine, testing compression….

Anyone have any ideas??? Thanks in advance! FYI… anyone want to buy a scarab? Smh!

 

[JetBoat195G]

It could potentially be condensation in the gas. I've been struggling with a similar issue recently, but it seems to be improving, as I've continued to feed it premium gas with stabilizer each outing. I've attached a thread that discusses P0300 and P0301.

 

[JoeSpear]

It could potentially be condensation in the gas. I've been struggling with a similar issue recently, but it seems to be improving, as I've continued to feed it premium gas with stabilizer each outing. I've attached a thread that discusses P0300 and P0301.

Thanks! I would think that would affect both motors, and not be isolated to just one cylinder. I’ve run 3-4 tanks of fresh premium through it also, which should have flushed any bad gas or condensation out. Was your issue isolated to one cylinder?

 

[JetBoat195G]

It was isolated to one cylinder. I was getting the same P0300 and P0301. My theory (could be totally wrong) is that around 5000 rpm the bow of my boat is as high as it gets, so any water in the bottom of the fuel tank is shifted aft. Water is denser than fuel. Cylinder 1 (P0301) is also located at the aft end of the fuel rail. This could all just be a coincidence. However, I did wonder, why P0301, and not P0302 and P0303? I replaced the spark plugs, and I noticed a somewhat progressive difference in the appearance of 1, 2, and 3. I have attached two images. I add Sta-bil fuel stabilizer every time I add fuel, and Sta-bil claims to remove water from fuel, again, maybe just a coincidence. My surging at 5000-6000 rpm and my P0300 and P0301 codes are now gone, but I am currently addressing a P013F/P0136 oxygen sensor issue, which clouds things a bit.

 

[JoeSpear]

Thanks for that info, that's a great theory! It sounds like we are having nearly identical issues. Glad yours is resolved, I hope that is all it is for me. Ill start pumping Sta-Bil through mine and see if that works before I start messing with swapping out ECUs and wiring harnesses..... will keep the page updated.