New to me 1997 Challenger 1800 - maybe dead MPEM?

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Doug Overkill

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Hi all. I have recently acquired a 1997 Challenger 1800 and when not working on it, I have spent countless hours on this great forum learning about the boat. Thanks for all the guidance so far.

Here is what I have been able to determine is going on in my boat. Both engines run, but not at the same time. The port side starts and runs and everything looks/sounds okay. The right side just cranks and cranks no start. If I move the magneto feed wire from the back of the port engine and plug it into the right engine (and swap the spark plugs too) the right engine starts and runs. I was thinking it maybe a bad coil, so I swapped the coil and both engines can run on either coil but only when using the port engine magneto wire.

This is the 1997 boat so the wires run directly into the MPEM without any connector. Any ideas what else could be wrong besides a bad MPEM?
 
I would check the actual wires. Make sure they dont' have a break in them.

Does your boat have the external CDI units? I'm guessing they are internal of the MPEM.

Unfortunalty, if you don't find a broken wire... then yes... I'm guessing the MPEM went bad. (Sorry)
 
Yes this MPEM has the internal CDI. I think I have check all relative wires and not found any breaks. I have been able to start each engine with each of the coil/wire sets by swapping them around. So I am confident in them.

Has anyone else had a MPEM go bad that allowed one engine to run and the other to not?
 
I found something. Including more confusion...

The underlying issue is Left motor runs Right don’t. I have convinced myself that the issue is electrical or MPEM. If I swap the 6 wire connector (c31) that come out of the magneto housing and the coil feed wires then the symptoms switch sides. Both motors have decent compression and run ok when hooked up to left side of MPEM.

I have found and corrected a ground wire issue in the c31 wire bundle for the right motor and now I have a sometimes it starts and sometimes it don’t on the Right. When it don’t it cranks and my spark plug tester lights up but no where as bright as the left.

I have checked a bunch of the grounds and other elec connectors and still have a left that starts up and a right that starts sometimes.

Could it be the MPEM?
Could it be the DESS?
Any other ideas?

Not sure how a bad DESS effects one motor and not the other but I read thru all the wisdom I can find by WATERLUVR on this site and tried the bench test he explained.

There should be less than 10 ohms when measured across the center of the lanyard and the side contacts. My key measures as open (infinite ohms) across these. Does this mean the key is bad?
Sometimes I get 2 good beeps when plugging it in and sometimes I get 1 until I wiggle it. Sometimes I get 6? Couldn’t find this in the troubleshooting section????
Even if I get 2 beeps it doesn’t mean Right motor starts every time. But it does sometimes.

Thoughts???
 
Clean post with eraser. Ive had dess post go bad. Find a salvage seadoo and get the post. Did i mention dess post..:/
 
Been a while since I checked in but my project has taken a turn for the good. Sort of.

As a lot of us have discovered there are
No good answers to MPEM problems. Twin engine MPEM are getting real hard to find and I wasn’t willing to buy a 20+ yo solution that is known to fail.

Jess & Nick at Westside have a solution using Oem jet ski Mpems. Nice guys and worth talking to. Search this forum for their info. I decided to go a different route.

I tried a bunch of things and using an Oscilloscope was able to ‘prove’ my MPEM was bad on the starboard engine side. I even bought a dead MPEM so I could machine into the epoxy looking to discover if the board inside was reverse engineer-able to find the issue. No such luck. Getting the epoxy/potting solution out of the board components wasn’t possible. In the end I got creative and used a MSD 4255 on the one engine and the working MPEM on the port side. If the MPEM fails on that side I’ll add a 2nd 4255.

I have now gotten my boat back on the water with 2 strong running engines. The project I bought last fall had not been on the water with the MPEM issue in 4-6 years by at least 3 other owners who had bought this project before me.

The family and I are packing it up and heading to the lake in Maine to play for the 4th. Will be it’s first real outing. Hope I got all the kinks worked out.
 
I have a "new to me" challenger 1800; the port engine starts, the starboard does not. In your most recent post, you said "got creative and used an MSD 4255...."

MSD's Q&A section says that this unit does not replace the MPEM but works in conjunction with the MPEM.

You also said in a previous post that you used an oscilloscope to determine the the MPEM was indeed bad...can you please elaborate? What did you check with the o'scope?
 
If the one engine runs and the other doesn’t which was my issue. First swap the plug in the back of the motor which is where the pickup generates a signal for creating spark. Also swap the spark plug wires left motor for right. 3rd swap the wires that go to the starter relay. Now when you try to start the left the right should start and vise versa. I was consistently able to swap these and see that either engine was able to run and idle well but only when hooked to the left side of the MPEM. Proof 1 that right side of MPEM was bad.

For proof 2 I hooked up scope. The oscilloscope was hooked up to the wire going to the coil. Not from coil to plugs which will toast the scope. But the white wires from MPEM to coil. I found the right motor which wouldn’t run was given a signal that was about the same amplitude as the left but 1/5 as often. A dual probe scope allowed me to see the similar signals but definitely different.

One MSD enhancer can replace the ignition function of the MPEM on 1 engine. If the MPEM still cranks over both engines as it is supposed to, then the MSD should create the spark. You can run 2 MSD with no MPEM. You would need to customize a few more wires such as the starter buttons and everyone says you will loose the neutral safety and no start in gear protection. I think there is a way around that but having other issues before I get there.

This change over is Not very many wires and not crazy complicated. But not for those that aren’t mechanical. The wiring diagrams I got from MSD and the Seadoo factory had all the info but required some thought/logic to get everything together.

I don’t think a 20+yo performance boat is for the unable. Not many mechanics will touch them and the costs to pay someone else to maintain one can’t be justifiable over a newer boat.
 
I follow what you did and I understand and agree that working on this thing requires effort.

I did as you suggested...swapped port/starboard magneto/plug wires...starboard engine behaved the same; port engine ran just fine using the opposite setup.

This boat was idle for a couple years; previous owner had hip replacement surgery and after awhile decided to sell the boat.

Most of the issues to date are a result of having set idle for so long....many cracked (due to aging) lines; bilge pump exploded; sticky/dirty switches...etc.

My current theory is it's a fuel/carb problem. It appears the starboard carbs were taken apart; I recently bought the service manual on e-bay, and between the manual and comparing port to starboard...it appears that the carbs need attention.

A local guy says he can rebuild them; I've owned several 2 cycle engines powered devices; I have many of the carbs rebuilt; and none of them are the same after the rebuild.

I have him rebuilding the carbs now and am also searching for new ones.
 
If the port engine ran with the swapped setup then you don’t have an MPEM issue. Lucky!

Next up is check spark and fuel. These mikuni carbs are very rebuildable. Use Actual Mikuni parts. Beware of after market that look similar. My experience is since it’s unlikely that u can buy a new ready to plug in carb setup Buying something else just to have newer isnt always better. IMO better to Go through what you have. Unless really stored badly the aluminum body doesn’t fail. it may need some gaskets and needles and such. Lots of good info on here for those.

The Seadoo Carb Rebuild Thread
 
I follow what you did and I understand and agree that working on this thing requires effort.

I did as you suggested...swapped port/starboard magneto/plug wires...starboard engine behaved the same; port engine ran just fine using the opposite setup.

This boat was idle for a couple years; previous owner had hip replacement surgery and after awhile decided to sell the boat.

Most of the issues to date are a result of having set idle for so long....many cracked (due to aging) lines; bilge pump exploded; sticky/dirty switches...etc.

My current theory is it's a fuel/carb problem. It appears the starboard carbs were taken apart; I recently bought the service manual on e-bay, and between the manual and comparing port to starboard...it appears that the carbs need attention.

A local guy says he can rebuild them; I've owned several 2 cycle engines powered devices; I have many of the carbs rebuilt; and none of them are the same after the rebuild.

I have him rebuilding the carbs now and am also searching for new ones.


It's not difficult to rebuild the carbs. The hardest part is getting them off the block and on the bench.

GROCERY LIST: (Amazon is our friend)
1. Genuine Mikuni Rebuild Kits. They'll come with all of the gaskets you'll need as well as some additional ones for different carb versions. Just match up the gaskets for what's in the carb as you remove them since some are cut slightly different. DO NOT USE AFTER MARKET REBUILD KITS! The fitting and materials in after market kits could be inferior and degrade more rapidly.

2. Genuine Mikuni Needle Valves. Don't do what I did and do a full rebuild only to get back on the water and not be able to start the engines because the cylinders were flooded due to bad needles. Do the job right the first time.

3. Carb base gaskets: You don't want to reuse the old ones gaskets. If you reuse the old ones you risk running lean due to an air leak. That could result in engine damage. Don't risk it, get new gaskets!

REBUILD:
Don't Rush, take your time. Grab your phone and snap pictures along the way. It's excellent reference material.

Before your rebuild, carefully bottom out the low speed jet taking note of the number of turns. This looks like a T but is not the idle screw. In my case it's 1 full turn out. Gently bottom it out noting the number of turns. This way you can reinstall it the same as it was by carefully screwing it in until it bottoms out, then backing it out the same number of turns. Do the same for the high speed ( you may need to remove the plastic cap from the screw head). Remember some models have the high speed set to 0 turns out. So if it doesn't want to move, DON'T FORCE IT. It's probably already bottomed out. You'll want to remove these to replace the O ring gasket on each as they could dry out and leak. I'd also reference the correct spec for your ski model using the chart listed in the links below. Factory settings are ideal so don't mess with it unless you have to. If you need to deviate from factory setups, there may be other issues to address.
NOTE: There will be 2 O rings in each kit. Both will be slightly different sizes. I believe the smaller of the two is for the high speed and the larger is for the low speed.

Open one side and take note of the parts and gasket placements. Just open the side up and remove the gaskets, noting the locations and gently clean the housings. You'll want to match the gasket removed with what's in the rebuild kit discarding the old gasket. Make sure to remove all parts, and replace all gaskets using the ones from your kits.

When working with the needle and seat, first place a finger over the arm to hold it down, then remove be screw holding the pin in place. You do this so the arm doesn't pop off and you potentially loose the spring under it. Slowly remove your finger. Take each part off. Be careful not to loose the spring. The needle and seat are held in with a small screw and catch. Remove the screw and catch, then pull the seat right up and out. Replace with your new seat and valve set and reassemble. Be sure to install the new O ring on the seat.
NOTE: It may be best not to use a spring from the kits during the rebuild. Instead use the original spring you removed when you reassemble the carb.

After replacing all gaskets and reassembling the carb, do a pop off test. You'll need to do this. Reference the chart below for the pop off PSI appropriate for your carbs. Check out how-tos on;
1. Build a pop off tester.
2. Conduct a pop off test.
(I didn't build mine exactly how the video describes. I'm using a hand pump and not an air compressor. Picture attached.)

Carb Specifications: Sea Doo PWC Carburetor Reference
Build Pop Off Tester:
Conduct Pop Off Test:
Reference: (
Carb setup)

Bottom line, this all may seem difficult but it really isn't. It's a good opportunity to understand how these systems work and give you greater flexibility to get your machine running perfectly. This community if highly responsive and if you have any questions along the way reach out!

image1.jpeg
 
I have the same fault with my 98 challenger
Port engine runs fine
Starboard engine has no spark
I'm thinking of going down the msd path
Does anyone have a wiring diagram for this?
 
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