1998 GTX LIMITED dead MPEM vs bad voltage regulator

[EdwinBland]

I have a 1998 GTX LTD recently acquired.
History: It had a top end rebuild by previous owner. However, previous owner had wired the battery ground to the starter plus terminal…

I got it running after repairing the rear electrical box and replacing the rear harness with one pulled from a 99 GTX LTD donor. ( it has an unused wire since the 98 only has one coil control line). I also put a good AGM battery in it… borrowed from a running 99 GTX LTD.
Also tested with the other MPEM it came with… runs on either MPEM… with gas/oil manually injected into carb holes. All guages were working…

I put the carburetor back on today and fired it up… it ran for a few seconds and then lights out… the display went out.. it no longer shows any sign of life… I measured the battery at 14.9V on a HF voltmeter…seems too high…
I have two MPEMs… albeit one with a bad pin… I was previously able to run the motor on either of these…
I verified the ground wire lug to battery neg terminal is 0 ohms…
I’m thinking the voltage regulator is bad…
Needing a little guidance.

Ive read that some folks don’t recommend using AGM batteries on the older skis…
It seems like the MPEM is dead…
Any suggestions on how to test the MPEM are welcome.

 

[etemplet]

I'd check replace the rectifier. I have had a couple of skis go dark when the voltage is a tad too high. Once was I had just removed the battery from the charger and installed it. The ski would not respond. I waited a few minutes for the battery to normalize and the ski fired right up. All I use is AGM batteries on the skis.
You can unplug your current rectifier from the charging system to test. You can run the ski, the battery just won't charge. Give it a try. Good Luck !!

 

[EdwinBland]

Tx etemplet! understand the rectifier/regulator on the 98 GTX LTD is internal to the MPEM, so this model can’t be manually disconnected. I’ve ordered an external one to connect in. I’ll also go back and check all fuses, and grounds again.
Does anyone know the absolute highest voltage the MPEM is spec’d for as an input… before it self destructs?
I just need to figure out how to get it back to life…the battery charging is a bit secondary… until it’s running again…
I’ll start with adding the external regulator…

I’ve reviewed a few of the different schematics in this year and subsequent years… the 98 doesn’t show a regulator… but other years and models do… that seemed like a clue…

 

[etemplet]

What might be happening is over voltage so the MPEM might be shutting down. Not saying for certain that is the problem. You can disconnect the yellow wires from the plug and do a voltage test. Or test it in the same way by trying to start the ski.
I'm sure you checked the fuses and connectors on the MPEM and plugs. They are sneaky.

I was surprised at my 1996XP wouldn't do anything when I put in a battery I just took off the charger. Good Luck.

 

[EdwinBland]

I found the problem…
MPEM is OK.
I pulled the MPEM connectors all out and ohm’d all the grounds out…
The ground in the back electrical box was bad…
I didn’t have continuity between the 3.24 ground and the rear electrical box ground on the coil… cleaned it up and reinstalled the harness.

I also installed an external regulator as a retrofit.

Tx etemplet for the suggestions!

 

[Poormanracing]

Take the connector off the mag housing and look at it allot of times green cheese builds up and can be a head ache.usually a voltage spike or reverse of terminals won't hurt the mpem.unless some one put a 15 Amp fuse wear a 5 Amp fuse for mpem was installed by accident or on purpose.i agree with the no agm and new lithium batteries.the new batteries have more cranking amps and they run down more and that over loads the chargingvsystem if you let them run down more and use the ski to charge them back up.the charging system isn't a charging system by design it is a maintaining system.

 

[etemplet]

Yep those grounds will cause problems for sure. Glad you found it !!!

 

[EdwinBland]

Take the connector off the mag housing and look at it allot of times green cheese builds up and can be a head ache.usually a voltage spike or reverse of terminals won't hurt the mpem.unless some one put a 15 Amp fuse wear a 5 Amp fuse for mpem was installed by accident or on purpose.i agree with the no agm and new lithium batteries.the new batteries have more cranking amps and they run down more and that over loads the chargingvsystem if you let them run down more and use the ski to charge them back up.the charging system isn't a charging system by design it is a maintaining system.

Tx for the suggestion!

 

[Solo2882]

1997 Seadoo gtx 787, I kept popping 5amp fuses I checked to see if I had a bad diode on the MPEM and I didn’t. the 5amp fuse holder was not grounded. I did have a fair bit of corrosion in the black box next to the battery. I figured it was the wires connecting the starter relay. The starter relay was replaced.
So clean up all the corrosion, the best I could.

So today. I was going to take my ski to the river. But I always check it to see if it will run before I head out. So I fired up for a couple of seconds just to make sure everything is working. I know it’s prone to pop 5 amp fuses. Ski fired up right away. Ran really good. I shut it off and tried starting it again. Cranked over, but quit right away. No power to the gauges. I figured I popped another five amp fuse. So I put a new fuse in it and turned it over. Engine was cranking over but not firing. I could smell raw fuel coming out of the exhaust. I knew that it wasn’t getting any spark. So I pulled the black box apart. Pulled the positive wire off the ignition coil and I went to test it for voltage with my multimeter. When I Went to turn on the ski. No power to the gauges. I figured I blew another five amp fuse. But the fuse was good. The 15 amp fuse in the black box by the battery Was good. Both 15 amp and five amp fuses on the MPEM. We’re good. Tested for voltage at the MPEM. Was getting full battery voltage. But no power to the gauges no beeping nothing. When pressing the start button with the key in or off the post. I’m really concerned that the MPEM’s bricked? And these things are next to impossible to find here in Alberta Canada.

 

[EdwinBland]

I would check grounds in the black box by the battery. Take the wires off the coil and clean with a wire brush and reassemble. I have several 98 GTXLs and they often times have had bad grounds… with similar symptoms.