**Low Voltage at MPEM fuses** HELP Going to beach in one day!!

[IDoSeaDoo]

1997 SPX 787: I'm getting no beeps and no diagnostic beep when I press the start button 5 times. The ski ran just fine a week ago. I have the old type of MPEM, the messy one with all the wires everywhere. It has two fuses sticking out. They were both 15A fuses, and I quickly realized that one is meant to only be 5.

Anyway, when I measure the voltage at the fuses, I only get 8.5V or so. The battery is at a cheery 12.5 (and good, trust me, I've even hooked on another fresh battery to verify). I have another 800XP and checked the voltage at those fuses, and it's 12.5, like the battery.

I noticed that if I pull out the square magneto plug, it goes back to 12V. So the plug is somehow cutting my volts down.

So.... I did a risky experiment: I took a live wire straight from POS and touched it to the fuse lead on the lower fuse. Instantly, I got happy beeps and cranking back.

So what's my problem, bad MPEM, or a lousy magneto?

Please get back to me asap, I'm trying to achieve my lifelong dream of taking this thing to the ocean this monday for my vacation...

 

[IDoSeaDoo]

PS the other XP with the good MPEM is all apart and needs engine parts I can't take it instead...

 

[IDoSeaDoo]

rectifier seems fine

unplugging rectifier doesn't seem to solve anything

 

[IDoSeaDoo]

when I push on the start button, the voltage goes down to about 3V, then when I release, it returns back to 8.5, but not right away. It starts at 8, then slowly climbs up. When holding the 12v to the fuse, the plugs fire, and the engine cranks. Can I just rig a wire to constantly feed it voltage? Is this a stator problem?

 

[IDoSeaDoo]

well, just pulled the stator from the XP. put a ground on it and plugged it up to the ? MPEM, and same thing... 8.5V. Is this a diode problem?

 

[Bills86e]

Disconnect the VTS harness, just to rule that out.

 

[IDoSeaDoo]

I did, besides, it's been dead/gutted long ago. I made a custom relay assembly to work the trim up and down. I've tried unplugging that with no avail. Is this the bad diode problem I've been reading so much about?

 

[IDoSeaDoo]

Just went out to the ski this morning, put the key on the DESS post, and got two cheery beeps. Hit the starter button once, and now nothing. Wish I would've checked the fuse voltage before I hit the starter, but now it's back to 8.5V Anyone know where the diodes are on the MPEM's with all the wires coming out (two embedded fuses)? I think for now, I'm just going to hot-wire it.

 

[IDoSeaDoo]

The Hack seems to work...

So my MPEM hot-wire hack seems to be working. It may be eating the MPEM alive while it's doing so, but the ski runs great, and I'm gonna ride her for all she's got. After my vacation, I'll look further into the problem. I do believe it's that diode though. Anyone else ever replace the diode on a 1997 SPX mpem (the one with all the wires, not with big square connectors) Any suggestions would be greatly appreciated.

 

[IDoSeaDoo]

Just got back from the beach, the hot-wire worked great. I had the wire on a switch, and while I wasn't riding, I'd switch it off (in case it's bad for the MPEM). On the 2nd day, with the switch OFF, the MPEM decided to work again... Then yesterday, I had to turn the switch back on as it died in the water. Do I have a phantom problem, do the bad diodes cause intermittent voltage leaks?

 

[Bills86e]

I'd say yes. VTS is also a potted electrical module, and the internal reed often fail from moisture permiation. Grease is our friend. Even it can't prevent the inevenable.

 

[IDoSeaDoo]

The VTS on this machine has been gutted and rewired. Since the unit was totally dead, I removed the circuit board, and wired the motor to two relays that interface with the handlebar switches. The motor works, but the gauge doesn't. Also, I never know when exactly to stop pressing the button, so maybe, when the VTS bottoms out, it sends a voltage spike when the motor tries to keep turning... This could be what's making it freak out... If I put a reset-able relay on this circuit, would that help with voltage spikes?

 

[Bills86e]

Options: Replace the module houseing, or trimfix.com

Check your rubber boot, before that fails.

 

[IDoSeaDoo]

Rubber boot is new as of last year. Will check for leaks this weekend though. I don't want to spend 100's of dollars on VTS (have another XP with working trim). I was thinking of rigging up some sort of custom led indicator in the housing, sort of like the fuel sender, but simpler... only concern is the current spikes when motor bottoms out. Anyone know how many amps those motors are supposed to draw when they first start changing the trim? I'm thinking 10A should be good...

 

[Bills86e]

NOT. The protection fuse is rated 7.5 amps. Its a friggin Nissan window motor.

 

[Bills86e]

I think he is talking about the DEI 451M. Intended to control auto door locks on alarms but apparently works well for failed VTS boxes.

 

[IDoSeaDoo]

so if I use the DEI 451M, would that not send a voltage spike through the system when the motor bottoms out?