CD Box/ Engine missing problem

[Bobby Smith]

I need a little help diagnosing a problem on a friends 70T. The car had a miss/stumble in 4th or 5th gear under load but only when it was warm. When the engine was cold it ran fine. I went to look at it and since I had a spare CD box( new Permatune), we tried that first and the problem was solved. The car ran great hot and cold. He drove it for about a week and all was OK. We met up the following week and after he shut the engine down it would not start again. We discovered NO fire and for grins plugged in his old CD box and it fired right up. It now has the old miss/stumble problem again. The old CD is the original Bosch and the new box is a Permatune. I'm wondering if something in the wiring is bad. Also wondering if something in the car destroyed the Permatune box but will allow it to run poorly on the Bosch box. Any thoughts or ideas would be appreciated.
Bobby

[304065]

Bad ground somewhere killed the CD. Either that or a coincidence. Try an MSD 6AL and make sure the grounds are correct, including the trans to chassis ground strap.

[Bobby Smith]

Will the tach work with the MSD 6AL?

[edmayo]

For originality you could send the Bosch box to Systems Consulting and have it rebuilt. Then nothing has to be changed.

[Bobby Smith]

Thanks Ed. I'm a little afraid of putting on another good box until we find out what happened to the brand new Permatune. Any thoughts?
Thanks,
Bobby

[edmayo]

Just one Bobby, we replace a lot of Permatunes, considering their age compared to 40 year old Bosch's that's not too good. My feeling is, those cars worked great for 40 years with the Bosch C.D. why change things and create yet more difficulties.

[Tom F.]

My two cents' worth: as good as they are, the Bosch CD boxes can work intermittently when they get old. The Permatune ones always suck. I experienced exactly what you describe in my 71. An MSD made the 3.0 liter run great, much better than the Bosch unit ever did. I know that it's heresy, but I think that every non-concourse early 911/930 should be running around with an MSD in it. I still run the stock Bosch in my 73.

When I bench tested my Permatune, it melted the power lead. That made me worry about the state of the wires in my car, but I seem to have escaped any damage, there. Try the MSD on the bench - you'll be impressed by the spark that it throws.

[chiroracer]

My experience is that the bosch units work or they dont. someone told me they ground out from the inside(?) best of luck, try a rebuilt bosch unit.

[Bobby Smith]

Hi. Wed. drove car to dentist ,about 30 mi., 45 mins.to 1 hr. latter ,start car
and it dies and will not start. Plug bosch unit up and car starts and runs. Still
misses a little in 5th and so on but starts and runs. Today (fri) ,plug permatune
up and car runs. Driving me crazy on what is going on. Latter. Boggie down
baby on monday.

Hey Guys, I received the above e-mail from my friend today. Any other ideas what his problem might be?
Bobby

[Flieger]

Bad ground somewhere killed the CD. Either that or a coincidence. Try an MSD 6AL and make sure the grounds are correct, including the trans to chassis ground strap.

I think there is some wiring issue separate from the CDI box.