96 XP 787 electrical issues

[Waternut]

I have a 96 xp with the 787 engine that I recently purchased. I cleaned up a ton of stuff and got it running properly but there is an odd electrical gremlin that I can't seem to figure out. I don't recall this being an issue before I removed the gauges and reinstalled them but when it's in the garage, I typically leave the DESS key on the ski so it could've been like this all along and I never trigged the problem.

The DESS key works but only if it's connected before power is supplied to the MPEM. If I run the engine and then pull the key regardless of whether it's running or not, the starter button does nothing...no clicks, nothing. There is still 12v running to the MPEM and relay inside the e-box but nothing happens. If the DESS key is connected prior to connecting the battery, it'll start, stop, and restart as many times as I like providing I don't pull the DESS key.

Here's a video I took of what's going on. Of course, I managed to fumble the restart after reconnecting power but you should be able to get the idea and that hasn't happened before. Normally I reconnect the fuse or a switch and it fires right back up.

 

[artr]

So in your video you do not get 2 beeps when you attach the key to the post. The beeper is probably not working which would not be an uncommon problem on an older ski. I would try the following:
Clean up the inside of the key cap and the connections on the DESS post with a pencil eraser and then some rubbing alcohol.
If that does not fix the issue then test the Black and Black/Yellow stripe wires that run from the DESS post to the MPEM (at the MPEM box). They should read 0 ohms with the key on the post and open circuit with the key removed when tested with an ohmmeter.
If you do not get the 0 ohms with the key on the post then try placing a stronger magnet near the post or check the connections of those 2 wires to the post. If you cannot get the 0 ohm reading with those tests then the magnet switch inside the DESS post may not be working and the DESS post needs to be replaced or the magnet on the key cap has weakened where it will not close the switch in the DESS post. It would make sense to replace the DESS post first.

You should replace the beeper if it is not working because it will alarm if the ski is overheating. It gives other error conditions also. They are listed in the shop manual.

 

[etemplet]

As said above do those checks. I would add a check of the mag plug. Sometimes the wires and connectors inside the plug corrode. I've had this happen a number of times. Instead of powering up the battery, leave the battery connected and unplug and plug in the mag harness. Also, there is a ground wire at the back of the ski that connects to the battery. I've had those wires corrode internally or a bad connection. If that ground is weak the ski will not do anything. Good Luck !

You should fainly hear the battery disconnect solenoid pull in when you install the key. Check that fuse but I doubt it is bad. On my 1996 GTX I had an intermittent start problem. I worked on it off an on a number of times. I removed the rectifier in the gray box and found a wire smashed underneath the rectifier. That was my problem. Also clean all of your plugs. A bad connection is a bad connection.

 

[Waternut]

@artr and @etemplet The DESS key and post are all good and check good. I even swapped them for a known good one with no change. I tried changing out the rear electrical box with one from a 97 SPX with no change. I tried disconnecting/reconnecting the mag harness but that doesn't do anything. At this point, I've literally spent weeks and and countless hours trying to understand what's going on. Everything works as it should when testing and giving it voltage. Everything is getting voltage the way it should but doesn't do anything. I feel like the relay inside the forward ebox could be the culprit since that's what clicks when I reconnect power but it gets power all of the time and works perfectly on the bench. Maybe it's really the MPEM and I can't properly test it.



Anyway, today I decided to just completely canibalize the forward ebox from that same SPX with DESS key and it fires right up and acts perfectly normal. Something is going on inside the 96 XP ebox. Hopefully I don't lose too much but I think there may be a slight rev limiter drop and maybe some spark timing differences. I lose the multifunction gauge with the SPX box but that didn't work anyway.

 

[artr]

I would test the 12V output of the holder relay that is shown in your picture above. That is the red/purple stripe wire that powers the CDI module when you put the key on the post. It must be at 12V when you get the ski to start and run. Test with a voltmeter that it returns to 12V when you remove and replace the key on the post. If it does not supply 12V after removing and replacing the key on the post then try removing the 15A fuse and replacing it with the key on the post to see if the 12V returns to that wire.

 

[etemplet]

I thought I had trouble with the holdr relay on my 96 GTX. My hearing isn't very good but I could hear it when it pulled in if the shop was quiet. LOL If they don't pull in, you'll get nothing. You might have an internal issue on the MPEM. I probably have a spare.

 

[artr]

I had a problem with my holder relay where it pulled in but intermittently but lost contact when the engine tried to start. I started to look at the relay more closely when I heard 4 beeps when I put the key on the post which indicates the MPEM cannot communicate with the CDI. I can not remember if it did not respond to the start key when that happened or not. Since the beeper is not working in this case it would be a simple test to rule out the holder relay. The only way to effectively test an internally malfunctioning MPEM is to replace it.

 

[etemplet]

YOu can run a lot of tests on the MPEM but they don't tell the whole story. When I troubleshoot these skis I don't look so much for the problem but find out "what isn't the problem." That is much easier to proove. LOL Too bad you don't live near me. I have complete gray boxes. Good Luck.