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Mpem
- Thread starter Jsullynz
- Start date
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Charging is the biggest issue. A defective VTS can fry them as well. Very common to smoke the MPEM when the VTS is bad. If you pull the VTS fuse then you won't hurt the MPEM.
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Spimothy Leary
Well-Known Member
I assume failure is also quite random, after all, they are electronics, stored in wet/musty conditions, used in harsh situations with a lot of bumps and vibration.
I was just discussing this the other day with Tonka, i've probably pulled 40 MPEMS over the years (small sample size) and I have yet to come across a single bad MPEM, (knock on wood), he has seen a bunch of bad ones (well over 100) with a variety of issues and possible causes.
I was just discussing this the other day with Tonka, i've probably pulled 40 MPEMS over the years (small sample size) and I have yet to come across a single bad MPEM, (knock on wood), he has seen a bunch of bad ones (well over 100) with a variety of issues and possible causes.
SabrToothSqrl
Well-Known Member
Jump-starting the ski from another source will fry an MPEM
Hooking up a battery backwards is the biggest culprit. If it doesnt wipe it out on the spot, you have done damage and at some point it will eventually go bad. Could be years...but thats my theory when a guy buys a machine and the 5 amp fuse issue happens out of nowhere.
Like the VTS, the potting can pull away from its plastic housing exposing electronics to the environment. If I have time I typically run a bead of silicone around that seam before I sell/ship a MPEM.
I would really like to know what causes the CDI side (no spark) to go bad. Last summer this was happening at an INSANE amount on 97 GSX mpems.
Typically chargers dont cause problems unless you are using the 50amp "engine start" modes. That will wipe them out almost every time. I dont take chances...even with my Optimate, I unhook the positive wire.
Jumping them off running machines is a very BAD idea. Jumping off another battery shouldnt be an issue.
And lastly...Jump packs...Im not sure if they have circuitry to boost amperage or what...but I always side on only using them as a last resort.
Like the VTS, the potting can pull away from its plastic housing exposing electronics to the environment. If I have time I typically run a bead of silicone around that seam before I sell/ship a MPEM.
I would really like to know what causes the CDI side (no spark) to go bad. Last summer this was happening at an INSANE amount on 97 GSX mpems.
Typically chargers dont cause problems unless you are using the 50amp "engine start" modes. That will wipe them out almost every time. I dont take chances...even with my Optimate, I unhook the positive wire.
Jumping them off running machines is a very BAD idea. Jumping off another battery shouldnt be an issue.
And lastly...Jump packs...Im not sure if they have circuitry to boost amperage or what...but I always side on only using them as a last resort.
DavesNotHereMan
Active Member
Ok, I got a question. The manual says to remove the ground cable from the battery first (and I assume it is therefore attached last). I always thought you disconnected the positive first to avoid inadvertent grounding and the "Oh Sh$&@?!" as sparks fly. Could hooking up the + side first screw with the MPEM?
-Dave
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-Dave
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soccerdad
Well-Known Member
OK, you can't just jab and run. What do you feel the correct info is? This is a really open forum with good information. If you have good information, post it please.
Sportster-2001-951C-Stock
Well-Known Member
Always disconnect the ground of any 12v battery first and reconnect it last, on any vehicle. The reason is, as you swing that wrench around it's more difficult to accidentally cause arcing and sparking, hot metal flying across the garage and messy stuff like that b/c a wrench at ground potential can't short out to nearby grounded objects.
Once the ground terminal of the battery is disconnected, current cannot flow and you can short the positive terminal to ground all day long and still current won't flow.
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Sportster-2001-951C-Stock
Well-Known Member
Voltage spikes basically, are hazardous to semiconductor devices. Too much voltage and/or reverse polarity, electrical problems, all of these can ruin the rather fragile MPEM.
I'd have to guess the CDI eventually fails as there is a capacitor involved I believe, and capacitors tend to fail after some period of time, capacitors are often a sort of chemical device and the chemicals dry out or water moisture enters and shorts it out. JUST my guess, I've never actually denuded an MPEM to uncover the truth.
Ceramic capacitors last a long time id think. Electrolytic would probably fail sooner.
For when the vts fails I believe its the back EMF that causes damage. Its like charging a coil and letting it discharge with quite a bit more voltage than you put into it. Id think thats what is happening when the motor doesn move but the connection is still good to the coil.
Jumper packs. Some put out higher voltage. I had one that was 13.7 at rest!
I'm in for removing the ground first as well. It was also explaines to me once that rhere would be a smaller spark. Not sure how...
One way to look at it is that the spark would happen on the other side of the vent !
For when the vts fails I believe its the back EMF that causes damage. Its like charging a coil and letting it discharge with quite a bit more voltage than you put into it. Id think thats what is happening when the motor doesn move but the connection is still good to the coil.
Jumper packs. Some put out higher voltage. I had one that was 13.7 at rest!
I'm in for removing the ground first as well. It was also explaines to me once that rhere would be a smaller spark. Not sure how...
One way to look at it is that the spark would happen on the other side of the vent !
Sportster-2001-951C-Stock
Well-Known Member
I think to lose the CDI part is not operator error, it's old age or possibly moisture. And by old age, I'm not calling you an old koot!
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DavesNotHereMan
Active Member
Well, now I need a little more assistance, please. Don't mean to hijack the thread, but let me know if I have this right.
If I got this right, removing the battery ground first will not allow the battery to complete any circuit because the negative of the circuit is "open" at that point. A voltmeter from positive to an engine ground will show nothing since there is no way back to the battery.
So trying to wrench the positive terminal first and grounding the wrench will cause sparks to fly because the common ground is still connected to the battery.
Right?
-Dave
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If I got this right, removing the battery ground first will not allow the battery to complete any circuit because the negative of the circuit is "open" at that point. A voltmeter from positive to an engine ground will show nothing since there is no way back to the battery.
So trying to wrench the positive terminal first and grounding the wrench will cause sparks to fly because the common ground is still connected to the battery.
Right?
-Dave
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Sportster-2001-951C-Stock
Well-Known Member
One thing I hope you will check though is the primary resistance of your ignition coil. I think it's possible if the primary resistance is too low this may cause some damage to the CDI transistor. So I guess if you want to play it safe you could replace the ignition coil. Only a guess though.
Sportster-2001-951C-Stock
Well-Known Member
That's correct, DNH
DavesNotHereMan
Active Member
Thx.
-Dave
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-Dave
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Sportster-2001-951C-Stock
Well-Known Member
No problemo. And FWIW, the opposite would be the case if you were an old koot like me, working on a positive ground system.
DavesNotHereMan
Active Member
Well, Sportster, I am an old koot. I used to drag race a 65 Mustang on Sunday, Sunday, Sunday at Detroit Dragway, so somewhere rattling around in the cranium mush, I should have remembered that. You helped reconnect the dots and I appreciate it.
-Dave
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-Dave
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69boss
Active Member
About disconnecting the battery, on cars disconnecting the negative side first is prefered. Reason is you can't short it out. If you disconnect the pos first and touch ground you have a spark, not so the other way around. There shouldn't be a voltage spike either way unless some item is powered up.
Seadoodoc
Active Member
Seriously you guys are killing the forums intelligence electrically. Lets make this really clear from a 25 yr Seadoo Mechanic and Car Stereo veteran. There IS NOTHING you will do on battery via connection sequence or charging method that will affect electronics. The idiot rules stated are strictly for idiots who occasionally appy reverse jump- start on vehicle. Yes.. I am included on list of idiiots! I may have screwed up a lot of expensive shit.. but your 20 yr old MPEM failed same reason my kids civic electric window mtr failed.. no blame just broke! 
AdamXP800
Well-Known Member
I'm not doubting you or challenging your knowledge. This is a laid back forum and we all enjoy discussion. But I've personally witnessed a ski jumped off by a running car fry an MPEM. I don't think it's coincidence it just happened to fail
96 XP800!
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