2012 EX343 won't idle/misfire?

[cmsmithx]

I have a 2012 CES EX343 (that I put in a 2006 226 Team). Ran great for a months. recently after a long idle, it died and would only restart with some extra throttle. New potentiometer, throttle body, then after a new cap and rotor it would start normal and run fine with no misfire. Then we took it on a 2 hour cruise for Christmas Eve, and on the idle back to the dock, same symptom. Plugs were new, now new wires and same symptom. ECM was re-programmed for new potentiometer, no difference (before the latest problem). Tomorrow we check grounds. Another new cap/rotor shows up after Christmas. Anyone have any ideas? Mechanic who programmed the ECU saw misfires on 1 & 3. With some other software, I see Idle Trim Low on bank 1&2 after a full throttle run (before the idle issue). I want to point to electrical issue, but could it be another sensor? Could it be fuel supply? Filters replaced (Fuel Module Filter replaced before install, spin on replaced again recently). Please don't hate because it was 70's in Texas today, we will get our cold weather...

[NautiqueJeff]

That's going to be tough to diagnose over the web. Best I can say is hook up Diacom and see what it is showing when the issue happens.

[cmsmithx]

Unfortunately I don't have Diacom... When on Diacom the tech could see the misfire, before I swapped cap and rotor. Plugs were fouled, so I started there. no improvement until I swapped cap and rotor and it would now Idle. Until it didn't after a couple hours. When it has had all night to cool, will try tomorrow, and check all the grounds. I also swapped the coil, because I have an extra, no change.

[NautiqueJeff]

One thing that you might check is to see if the distributor cap mounting screw holes are damaged. This is common on the Vortec distributors, and normally means that the distributor has to be replaced. Check out the thread below for more info.

https://www.planetnautique.com/vb5/f...calibur-engine

If this is the case, I have successfully used a repair plate to fix this issue in the past.
https://www.amazon.com/Dorman-90449-...97110383&psc=1

[teamseal]

I have a 2012 CES EX343 (that I put in a 2006 226 Team). Ran great for a months. recently after a long idle, it died and would only restart with some extra throttle. New potentiometer, throttle body, then after a new cap and rotor it would start normal and run fine with no misfire. Then we took it on a 2 hour cruise for Christmas Eve, and on the idle back to the dock, same symptom. Plugs were new, now new wires and same symptom. ECM was re-programmed for new potentiometer, no difference (before the latest problem). Tomorrow we check grounds. Another new cap/rotor shows up after Christmas. Anyone have any ideas? Mechanic who programmed the ECU saw misfires on 1 & 3. With some other software, I see Idle Trim Low on bank 1&2 after a full throttle run (before the idle issue). I want to point to electrical issue, but could it be another sensor? Could it be fuel supply? Filters replaced (Fuel Module Filter replaced before install, spin on replaced again recently). Please don't hate because it was 70's in Texas today, we will get our cold weather...

Like Jeff Said look at the distributor housing for cracks or fastener boss damage. read the plugs also.
If it all looks good and no problems i would do a leak down test on cylinders 1&3 and check for cross migration. the vortec engine does have a record of doing this. a small grove between cylinders where the head gasket blows out will create very similar issues. being that this blow out will not show water in the oil, if this is the case and the grove between cylinders is not to deep the block can be decked and put back into service. since the vortec engine came out in 96 i have seen two engines do this in ski boats. both engine's were to far damaged to machine or repair.

[cmsmithx]

A little more background while I wait on a few parts - the wiring harness at the crank position sensor had been damage. It may have shorted reference voltage for other sensors, as I eventually had failed water temp sensors (all of them eventually failed). I replaced them all. Plugs were fouled after the first time this problem happened. I have a new MAP sensor on the way. I plan to replace the MAP sensor, check fuel pressure, and if still happening, replace the cap/rotor again. I did pull the new cap back off yesterday, screw mounts seem fine, but I will inspect closer when I get back to it Wednesday or Thursday. Strange that it was immediately fine when I did the cap and rotor last week, then failed again.

[jpwhit]

Contaminated fuel can cause the sporadic issues you’re describing. I have an auxiliary gas tank that I use to confirm or disprove if bad fuel is causing an issue.

[cmsmithx]

Short term update - New MAP sensor came in today. Installed and boat fired up immediately and idled without problem. Will put some time on it tomorrow and see how it goes. Will report back good or bad.

Update - so far so good. Stll idlng fine, and seems to run a little smoother. Had a random stumble a couple of times running 1500-2000 rpms, will keep an eye on that. Might run some injector cleaner through. Gas is fresh and treated with stabil 360.