96 XP random misfire

[tingraham]

Hi all,

I am having an issue with what seems to be a misfire/skipping at mid to high RPM. It flies right along but just stutters randomly but often like every 1 second or more often. I can still get it to about 45-50 even though it is doing it but it is quite obnoxious and definitely lacking the full power because of it. This is a continuation of an issue that I was having last year which from what I can remember when I put it away last year it was hitting a wall at about 4800 RPM that sounded almost exactly like a rev limiter. We came to the conclusion that it was ignition related so the first thing I did when I got it out this year was pull the mag cover and check out the trigger. First thing I noticed was that one of the trigger pad things on the mag cup with quite rusted from what I assume was water that got in that front cover for awhile and rusted just the one pad. I took a small wire wheel and abrasive wheel and cleaned it up nice and shiny (as well as the one that still looked pretty good). I also did a static resistance test on the trigger and it fell within specs so I put her back together and went for a test to find this now misfiring type of thing that is way less consistent than the issue had before I put it away for the winter. I proceeded to throw a new ebox in it with a new coil, wires and such to see if that was the culprit and it made no change. I then tried out a different CDI and that had no change. So my next swap will be the trigger coil, but I just have a feeling I will be disappointed as that just seems to be how it usually goes with these lol.

Side note: the carbs have been gone through like a million times as well as the rest of the fuel system. It REALLY feels like ignition issue to me and after I swap the trigger coil I think that covers just about every ignition component on the thing unless there is something I am missing. Oh and the voltage regulator shows good readings and I also tried a new one on it with no avail last year, granted it was a tad different last year.

here is the link to the thread discussing the original issue:
https://www.seadooforum.com/showthr...s-like-rev-limiter-between-4-5k-rpm-when-cold

thanks for any input!

 

[Matt Braley]

Check the white wire for pinching or chaffing. That's the signal wire for the coil.

Look inside the connectors and make sure no pins are green with corrosion or pushed back in the plug. Trim back the leads and screw the plug boots back on till they stop turning. Di-electric grease on everything. Clean connections on the base of the coil and make sure the lag tightens or replace it with one that will.

 

[tingraham]

Thanks for throwing some ideas around already, Matt. I guess it is always a possibility, but I changed out literally the entire ebox (solenoid, coil, wires inside the ebox as well as the plug wires and ends) and it did not change even a tiny bit of how it is acting which points me back to either the white wire outside of the ebox to the mpem box or the trigger it self I would think. Do trigger coils ever go intermittent or is it usually all or nothing on them?

 

[Matt Braley]

Usually they are acting up because they are magnetic and attract shavings made by the starter/flywheel over the years. That and the early brackets would break off. Make sure yours is not cracked. If they are starting to tear they can vibrate too much and throw things off.

Yes check connections between the boxes and the wires inside the grey box. The wires going to the CDI love to get pinched between the plastic halves.

 

[mikidymac]

Mine had the exact same symptoms and it was the voltage rectifier. You can unplug the red wire I think and try it but it won't be charging. Mine also showed 15volts when checking the battery and the engine reved to 3000 rpm on the trailer.

 

[tingraham]

Well this took an unexpected turn. Fired it up on the trailer to test voltage regulator again (voltage didn't go above 13.6 btw). Gave it a little gas to make sure voltage didn't spike and the driveshaft snapped. Anyone ever see this? I just pulled the pump off and threw my alignment tool on and it's not out of alignment so pretty strange.

 

[tingraham]

This continues to be an on-going issue. Can't reach max rpm because of the misfire like issue. Before I cleaned the pad on the mag cup it would only rev to 4800 rpm. Now it revs to 5700 rpm but stutters like a misfire. I have replaced the trigger coil, cdi and entire ebox. I'm starting to think I should put a new flywheel/mag cup on it but I find it hard to believe it's the issue.

 

[tingraham]

We have success!!!!! It always drives me nuts when people don’t close out a post with the solution so I wanted to be sure I did.

I pulled the motor and tore the top end down to check it out for the heck of it. In doing so I went ahead and deglazed/honed the cylinders as the piston and cylinder walls still looked pretty decent still. I got a top end gasket kit and replaced all the gaskets in reassembly. It appeared that the motor had never been apart before, at least the top end. After assembling it and reinstalling in the ski, the problem is completely gone!

My theory is that either the cylinder base gasket or one of the o-rings at the top of the cylinder was allowing water to slip by at a certain water pressure/rpm and into the combustion chamber thus making it run like trash at a particular rpm.

Now, if you are reading this in the future and your ski is having a similar issue, this is how I should have tested it- put the ski in the water and confirm it is still having the issue. Clamp off the water supply line to the engine and run one quick pull with it to see if it goes away or at least changes behavior. That would have immediately pointed me in the direction of ripping the engine apart sooner.