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-   -   Bosch 3 pin MSD question, long! (http://forums.pelicanparts.com/porsche-911-technical-forum/110111-bosch-3-pin-msd-question-long.html)

Skip Newsom 05-09-2003 06:01 PM

Bosch 3 pin MSD question, long!
 
Alrighty then...
I have a 72 T that I saved from falling too far apart in the PO's garage.
It had been sitting for a few years and I've gone through the fuel, electrical, ignition, brakes, replaced fluids, hoses and even dropped the motor and tranny chasing oil leaks and cleaning.
A million thanks to this board for all the know how and encouragement on the journey!

The situation I've run into now is this:
In my trouble shooting to bring the ignition back to life, I diagnosed that the MSD and/or coil were dead. I replaced them with a Permatune CDI and new coil. Life got much more fun with a living breathing (smoking, dripping) 911...

After several more months of tuning and even a couple of visits to Mr. Walker (yes! he deserves the praise he gets here) the car is running reasonably well and I got to wondering if the original Bosch box was my problem or a bad coil... so I stuck it back in the car.
It ran better than it ever had, a low RPM stumble was gone and it pulled well to red line. I drove it for a couple of days. (I had the Permatune box + tools along just in case)

Then, trouble, I fired it up to head home from work, it idled perfectly for about 25 seconds, then quit as if I'd pulled the coil wire and would not even spudder. I got out, checked fuses, pulled the cap... nothing, still would not start. I went ahead and changed back to the Permatune box, she fired right up and I drove home, low RPM stumble and miss was back too.

Now I can't help but wonder if the Bosch 3 pin box is repairable?
Anyone with sucess stories? I'd love to know what component usually goes out in them, and if I could repair it and enjoy a better running car again?

jeff m 05-09-2003 10:24 PM

Skip,
I went through this problem.
If the coil "goes", or is on the way out, failing when hot, it can take the box with it.
Coils are cheaper than boxes.
I have repaired a permatune (with Warren's help) I would imagine the MSD is similar.
I originally located my problem by waiting for it fail and checking the 300v output with a 600v neon.
If you search "permatune" and my username you will find a lot of info.
Jeff

Skip Newsom 05-12-2003 05:46 AM

Thanks Jeff!
The nice thing about the Bosch is... no potting!!
I'm still wondering if anyone out there has a wiring diagram with component values for the 3 pin boxs?

Zendalar 05-12-2003 05:58 AM

Well...here goes...there are different versions of this thingie..not sure if this is legal but moderator may remove it if he wishes:

http://forums.pelicanparts.com/uploads/CDI_diag3.jpg

http://forums.pelicanparts.com/uploads/CDI_diag2.jpg


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