Aftermarket MPEMs and Ignition Components 1996-1997 787s

[hafweigthr]

I am tired of fighting with old electrical components - reg/rectifiers - spark coils and wires - MPEMs. Have tried Arieltech MPEM on my 96 XP but not real impressed since I am getting intermittent running issues which are appearing like they are coming from the MPEM. What is out there to make these 787s more reliable and consistent?? MSD, etc. or are the OEM stuff the best. Also big problem is the reg/rectifier - does anybody make an upgrade or better one? The aftermarket ones are so far not worth much.

Maybe the Matt Braley's or others that modify these can help me out. Would like to keep my 787-2 strokes and make them more reliable.

[hafweigthr]

Re: Aftermarket MPEMs and Ignition Components 1996-1997 787s

Any input from the aftermarket/race guys???

[SpitAndDirt]

Re: Aftermarket MPEMs and Ignition Components 1996-1997 787s

At least with the rectifier/regulator, I can't figure out why they designed it to be "dual half-wave" design instead of a true 3 phase design used in nearly every automobile since the mid 1960's. A true 3 phase rectifier has a separate "diode bridge" with 6 discrete diodes for rectification. The voltage regulator portion is also discrete from the rectifier bridge.

In the OEM "Tympanium" design, they use only two Silicone Controlled Rectifiers for this purpose. Now, let me disclose that I am only an AMATUER electronics hobbyist. I've still got a heck of a lot to learn. Maybe SCR's were the way to go in the 90's in this marine specific design. Maybe the automotive style required some sort of external heat sink? In any case, here is my schematic drawing of the voltage regulator that I tore apart. Maybe you can use the information to improve upon the design. That was my original intent. I'm honestly surprised that after all these years, that all the original MPEMS haven't been mapped and schematics published on the web for other hardware hackers. I guess the potting material really kills the desire to open it up and see what's inside.

Now as for MPEM's. More than likely, the original designs used the highest quality components by Motorola and electrolytic capacitors by Nichicon, Rubycon of Japan, and United Chemi-Con. Read up about the great capacitor lawsuit of desktop computer manufacturers due to industrial espionage. Pretty interesting stuff. There's a freaking forum dedicated to the subject www.badcaps.net

Since there are so many other shady oriental companies manufacturing clones of brand name components, it brings the price down, but the life expectancy is probably a fraction of what the OEM stuff is. As a side note, electrolytic capacitors do have a finite life span. Once the electrolyte dries up or leaks out, the capacitor can no longer perform it's function of filtering or isolating voltage levels. This can lead to damaging the $10 Microprocessor that makes everything possible.

The Motorola Processor that has been pretty commonly found in dissected MPEM's is Motorola (Freescale and now NXP) MC68HC705PCP. This microprocessor has a operating temperature range of -40 to +85 degrees C. 28 pin count, 2,104 bytes of Electronically Programmable Read Only Memory (EPROM), and 128 bytes of user RAM. This thing is archaic by today's standards but so few people understand embedded systems which is why the original B.U.D.S programmer cost an arm and a leg and was only available to dealers.

I always find it ironic that D.E.S.S debuted at the same time that the automotive industry was mandated by the U.S. Gov and it's standards defined by the Society of Automotive Engineers to adopt On-Board Diagnostics, 2nd Generation or OBDII for short.

Hopefully this info helps in some way. It's not much but it's better than nothing. Cheers

[scensor]

Re: Aftermarket MPEMs and Ignition Components 1996-1997 787s

Why don't you go for MSD?

[scensor]

Re: Aftermarket MPEMs and Ignition Components 1996-1997 787s

Woah great research and knowledge!

[hafweigthr]

Re: Aftermarket MPEMs and Ignition Components 1996-1997 787s

I was wondering how different the DI - high current regulator was . Also was thinking I could use a full wave bridge on each phase and then a high amp regulator from a tractor/etc. for regulation. Putting in a water vehicle would be a bad idea since this would be a source of possible spark and seat liftoff if there was a gas leak.
Again all the aftermarkets have proven to be crap and not reliable unless somebody has some feedback on one I have not tried.