1999 Seadoo Challenger intermittent spark

[whealy22]

Hey Guys. First i just wanted to say thanks for having this forum. I'm hoping you guys can help me out!

So i am having a really odd issue that my friend and i just cannot get to the bottom of. The starboard engine seems to have intermittent spark. Here is what is happening: When we go to start the engine it starts but then dies on it's own after a few seconds, then it's very hard to start at all after it gets up to temp it seems. Even if we give it full throttle it still doesn't want to start. Sometimes it just starts up for a few seconds but then dies out. When it does run for that 3-7 seconds it doesn't seem to want to rev over 3-4,000 RPMS. It also does backfire after trying to start, which we both found odd. Compression is 148 in each cylinder and we did verify it will run on both cylinders when it starts for a few seconds but then dies out on it's own. Here is what we have done so far to fix the issue.

We replaced the pick up/trigger and while we were in there inspected the stator and housing. It was very clean in there. So we did not think it was the stator. We also replaced the spark plugs, spark plug wires and coils, we disconnected the red wire to the rectifier and tried running it with no change, we disconnected the 3 connectors on the MPEM, inspected them for corrosion and did not see anything and then put dieelectric grease on the connectors and reinstalled them, also cut the spark plug wires back 1/4 inch and reinstalled them. We could not see spark while checking the plugs for spark but yet the engine does try to turn over and start from time to time but like i said will not stay running. Also we checked the 2 fuse boxes below the MPEM and all good, we have gotten down to thinking it's the MPEM but they are soooo expensive if that's the issue i could be out for the boating season...

The other engine starts and runs fine.


Anyone have any other ideas? Is there something we are missing? If it is the MPEM does anyone have a cheaper or less expensive way of getting an aftermarket one or does someone reliable repair these units?

PLEASE help. lol. Thanks so much!

 

[ryffish]

There are guys on this forum that can sell you a MPEM very reasonable

 

[whealy22]

There are guys on this forum that can sell you a MPEM very reasonable

Ok. That's very encouraging to hear. Do you know whom I could contact about one on here? Or if anyone has one available please let me know. Thanks

 

[ryffish]

Look for his forum handle is Minnetonka for me . He owns a powersports shop he is the guy for the parts you need . I haven't heard from him in a while he must be busy

 

[ryffish]

Also his shop is west side powersports Google it he has a website he has all kinds of new and used parts

 

[Freight53]

You can swap mpem system wires and other items and try to chase the problem. My ski did this exact thing. Ended up being the mpem.

Ensure the battery is 100% charged also.

 

[Nike12000]

swap the mpem side to side and see if engine issue follows

 

[LouDoo]

Moving this to the 2-stroke sport boat forum.........

Lou

 

[jhjesse]

Run your bilge fan for a couple minutes before starting and see if it helps. Puts fresh air in the engine compartment.

 

[whealy22]

Thanks for the replies guys. So here is an update. I ordered a used MPEM that was guaranteed to be in working order and that DID NOT fix the problem. Of course, This model has the dreaded black box MPEM so there is no way to switch the wires on the MPEM. Luckily the shop i purchases the MPEM from allowed me to return it. They also have been EXTREMELY helpful with trying to diagnose the problem. So far we have yet to figure it out though. Here is what we have done additionally. We took the working rectifier from the other motor and changed it over and they did not fix the problem, we changed the mpem of course and still same issue, we thought maybe the motor threw the rotary gear, so we took off the carbs and put a screwdriver in there and tried to turn the shaft thinking the shaft would turn freely since we were thinking the gears have sheered but to our surprise the shaft did not move and locked up in place securely. The rotary valve itself looked good as well, i did notice small scratches on it but other than that it did seem fine. We did notice that there is oil on the rear cylinder plug when removed so we are now thinking that the rotary seal has a leak and it's allowing oil into the rear cylinder which is causing the boat to backfire and not start. We were told it is not the crankseal since the motor would most likely run even on a bad seal. Does this sound right? we cannot figure this thing out and feel like we have tried everything. It's very frustrating...is there anyone that has an answer? Please! We are going to remove the rotary valve cover tomorrow and check out the valve and gear and seal up close but if that's not it...we are pretty lost.....anyone have some suggestion?

 

[jhjesse]

Might be the flywheel key has sheared.
Might also check rotary valve clearance.

 

[Freight53]

The boat might start but will soon coat the plugs with oil and will not run. (If the rotary valve seal is bad) I've got a guy in Maine who has helped me out so much; has over 18 years in the business.

You should have 2 of everything, that said you can swap plug wires, rectifiers, and mpem going to the ignition coils. You're able to chase the problem it'll just take some creativity and take plenty of pictures prior to moving wires around to ensure you get those back in the proper positions.

Put a glove on and stick a Phillips screwdriver in on of the spark plug boots. Hold it very close to your spark plug top. Have someone crank the motor until it starts and watch the spark from the plug to your screw driver. You need to determin if your having spark or fuel issues.

 

[ryffish]

Have you tried cranking engine with plugs off . When you do oil will shoot out of spark plug holes then after you clear oil out it should run fine it happened to me once

 

[whealy22]

Hey guys...we have tried starting the boat without the plugs and no oil is shooting out which we found odd. We took off the cover for the rotary valve and gear and seal look good. We are pretty stumped here. Just cannot figure it out. We are now taking the motor out to check on the flywheel key and also it's just easier to work on. Any other suggestions?

 

[Freight53]

Did you determine if it's losing spark and shutting off, or losing Fuel and keeping spark until the motor pulley spins down.

 

[jhjesse]

Went back and re read your first post and payed a little more attention this time.
What makes you think it is intermittent spark? Usually you have it or you don't.
Have you checked and double checked all ground wires? Poor ground will drive you nuts.
Do you have a spark tester? They are ten bucks at the auto parts store, and you can lay them on the plug wire while it is cranking/running.
Have you ohm tested the stator?
What do the spark plugs look like? Chocolate brown or chalky white?
Have you measured the rotary valve clearance. Forget what the spec. 0.2 or something like that.
You have checked the compression and it is good.
Have you had the carbs off recently? If so, what was done to them. If not when was the last time they were checked/rebuilt?
I think you are checking for a sheared flywheel key right?

 

[Freight53]

Intermittent spark could be a cracked stator grounding itself. Would move with heat as the motor warms.