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battery disconnected stops running
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Sportster-2001-951C-Stock
Well-Known Member
The battery needs to be connected in order to limit the voltage spikes to a reasonable value, the battery functions as an instantaneous voltage spike limiter once the SCR's are switched on, else if the battery wasn't there to absorb current the full voltage across the stator would be on the output of the rr.
The battery limits the voltage spikes, it serves to condition the DC voltage by virtue of it's very small internal resistance.
Sportster-2001-951C-Stock
Well-Known Member
Here you can find the transfer function of a lead-acid battery:
http://www.mathworks.com/help/physmod/sps/powersys/ref/battery.html
Note this battery has a very low internal resistance, lower than your battery cables even, and large hysteresis. These factors act as a closed loop to limit the instantaneous system voltage that could otherwise cause the semiconductor junctions in the MPEM/PCM to break down and avalanche currents to occur across the junctions.
MPEM damage will be the result if the MPEM's semiconductors are exposed to voltages beyond their avalanche threshold voltage capacities. It doesn't take much current to damage a semiconductor if the avalanche voltage of the semiconductor junction is exceeded, especially in the case of a reverse biased junction.
http://www.mathworks.com/help/physmod/sps/powersys/ref/battery.html
Note this battery has a very low internal resistance, lower than your battery cables even, and large hysteresis. These factors act as a closed loop to limit the instantaneous system voltage that could otherwise cause the semiconductor junctions in the MPEM/PCM to break down and avalanche currents to occur across the junctions.
MPEM damage will be the result if the MPEM's semiconductors are exposed to voltages beyond their avalanche threshold voltage capacities. It doesn't take much current to damage a semiconductor if the avalanche voltage of the semiconductor junction is exceeded, especially in the case of a reverse biased junction.
68ragtop
Well-Known Member
Hense the little "do not boost battery" stickers that nobody ever notices..... .
(referring to the dirty voltages some of the chargers produce)
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Sportster-2001-951C-Stock
Well-Known Member
You're welcome.
Now back to our previously scheduled threads concerning pop-off pressure and maybe even an oil thread or two!
Space coast
Sportster-2001-951C-Stock
Well-Known Member
None available AFAIK, but feel free to post it if you find or make one by reverse engineering yours.
Inside you will find transistors, diodes and several IC's, probably a few capacitors as well.
68ragtop
Well-Known Member
There is no schematic of the MPEM itself as its not considered a serviceable item. Its one of the reasons everyone is so cautious with them. when seadoo went to the "all in one" design MPEMs in the late 90's, it really cleaned up the skis wiring process & I am sure it saved a lot of time in mfg the skis. But it made the electronics even a little less serviceable. there are a pile of pins on the "newer" mpems that are nothing more than a connection to another pin. They just pass right through in many instances. They build them, then fill them with an epoxy type potting material that's makes working on them all but impossible. I have tried removing that material from other components like VTS modules, & normally all that happens is you create more damage. This is assuming we are talking about the 98 GTX in your profile. Not sure on that.
If your trouble shooting a specific electrical problem, I would disconnect everything you can from the ski & work backwards. You never really told anyone what your trying to hunt down, or what model ski so I am not sure what to say, but I can tell you that normally if your blowing the 5A fuse its probably not good news for your MPEM. But again, I'm just making an assumption because you made a reference to the 5A fuse earlier.
Getting everyone's opinions on the forum takes a bit of a filter & an open mind. You have to take what you can from the information given from everyone's experiences. Collectively there is more experience & knowledge in this forum that would rival, & more likely embarrass seadoo dealers themselves. So if you ask the right questions its amazing what you will find here!
I am constantly learning more things on this site.
If your trouble shooting a specific electrical problem, I would disconnect everything you can from the ski & work backwards. You never really told anyone what your trying to hunt down, or what model ski so I am not sure what to say, but I can tell you that normally if your blowing the 5A fuse its probably not good news for your MPEM. But again, I'm just making an assumption because you made a reference to the 5A fuse earlier.
Getting everyone's opinions on the forum takes a bit of a filter & an open mind. You have to take what you can from the information given from everyone's experiences. Collectively there is more experience & knowledge in this forum that would rival, & more likely embarrass seadoo dealers themselves. So if you ask the right questions its amazing what you will find here!
I am constantly learning more things on this site.
Ya 98gtx problem was I thought was rectifier but it is not. And certainly not fuel related. An issue I have had for awhile bogging at mid throttle. Been through the fuel system twice. Swapped carbs. Removed selector valve and placed inline filter from tank to carb. I'm going to swap coil when I get home from Texas.
Sportster-2001-951C-Stock
Well-Known Member
Do you mean feels like a lean hesitation mid-throttle? Does pulling the choke perk it back up?
Sportster-2001-951C-Stock
Well-Known Member
Well, I also had a lean hesitation with my 951 and went through checking everything with a fine-toothed comb which was kind of a blessing b/c I found plenty of things that needed repairing, but finally I ended up increasing the pilot jets by two sizes and the lean hesitation is no more, no sign of it, nada, arguably 2 sizes larger may have been more than necessary b/c it does 4-stroke SLIGHTLY between 2000~3000RPM no wake speed.
One thing for sure, it's a strong runner and no longer falls on it's face.
One thing for sure, it's a strong runner and no longer falls on it's face.
Sportster-2001-951C-Stock
Well-Known Member
I'm running an #80 pilot jet with the original #162.5 primary jet and 2.0 seat orifice with black 80gr spring but my carbs are a little newer than yours, these are the later vertical shaft type.
I think I would've been okay with just a #77 pilot and the original 95gr spring and I bought the #77 to give a try but it runs great with the #80 so there's no hurry to make any changes.
Just some info about my current 951 setup that may or may not be helpful for you...
Another thought, have you given your reeds an inspection? I've noticed on reed motors if the reeds are a little tired and about ready to fall out it will begin spitting fuel out the carb throat at idle (intake reversion).
http://www.circletrack.com/enginetech/ctrp_1008_intake_reversion/
I think I would've been okay with just a #77 pilot and the original 95gr spring and I bought the #77 to give a try but it runs great with the #80 so there's no hurry to make any changes.
Just some info about my current 951 setup that may or may not be helpful for you...
Another thought, have you given your reeds an inspection? I've noticed on reed motors if the reeds are a little tired and about ready to fall out it will begin spitting fuel out the carb throat at idle (intake reversion).
http://www.circletrack.com/enginetech/ctrp_1008_intake_reversion/
Sportster-2001-951C-Stock
Well-Known Member
An engine running under high(er) load requires a higher gap voltage in order to make the spark jump, so yeah it's possible a weak coil can also cause similar symptoms. This is why we have to runs a narrow gap like we do on 2-strokes otherwise it's requires too much voltage to make the spark jump the gap through all that nasty wet oil and fuel.
In the case of 4-stroke FI engines, the leaner mixture requires a fatter spark (wider gap) thus higher voltage is necessary for it to ignite reliably, this is why the lean FI engines run such large plug gaps.
Sportster-2001-951C-Stock
Well-Known Member
That's what I'm thinking, the dead zone was really wide on mine, it occurred just off idle at no wake all the way to about 70% throttle, so it was a huge gaping hole.
One size larger should make a positive difference if your hesitation is just a fraction of that.
The #80 in mine is plenty fat though, it four-strokes slightly off idle from 2~3k RPM, but I have the 2.0 seat and 80gr spring in there also, which is different than yours, not sure if your air box is the same but man, your pop spec is considerably higher than mine.
And if your're not running a 2.0 seat then I'd do that too, the 951 is too lean on the top end without a 2.0 seat, and your primary jet is smaller than mine as well.
I'm not sure what other differences there are between your carbs and mine but if you have the SBN46 as opposed to the SBN46i then your fuel pump is smaller too, I think. I'm not sure if there was an non"i" version.
One thing's for sure, you seem to need more fuel.
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