78SC Euro New MSD coil, then back to old, still wont start -- any ideas?

[acapella8]

I purchased a used but working MSD coil from a friend.

Car was starting fine, no issues whatsoever, I just wanted to replace the coil (not knowing age of bosch) with the MSD.

The MSD coil says "MSD Blaster 2, for MSD-6, MSD-7 adjustable timing control, dual curve performance towing products AND stock ignition sysem."

I removed my existing BOSCH coil and installed the MSD.

Checked the (+) and neg (-) connections. And the wire coming from the distributor cap.

When I went to test the new, the car would not start. Turns over strong, but no start.

I replaced the MSD with the existing BOSCH.

Checked connections.

Still 78SC euro will not start.

Any ideas?

Help.

[acapella8]

Also, I should note I double checked all wires at distributor cap and wire from coil to cap.

[PorscheGuy79]

Good luck Tom, I wish I knew what to tell you but I will hope for the best. IIRC coils dont really go bad, FYI.

[acapella8]

Thanks dude. BTW - have been reading your brake cooling thread(s). I hope to get to that stage someday....good reading and fascinating stuff.

[Early_S_Man]

Does the tachometer move during cranking? More specifically ... is there a pulse train to the tach during your attempts to start? You can check it with an oscilloscope or CMOS logic probe on the Black/Violet wire on the TD terminal of the tach ...

You should check the output from the magnetic pickup coil [during cranking] in the distributor with AC Voltmeter set to 2 - 4 Volt range.

Green coax cable in good shape???

[acapella8]

Early_s -- Yes - the tach moves during cranking. I went and checked again.

Green coax cable is good.,,

Still no start...

[Howard M]

I believe if you look on the MSD web site for MSD 6A or 6AL CD installation they say that the stock Bosch coil is incompatible with the MSD CD. Reversing the logic, you may have done damage to the Bosch CD by using the MSD coil (lower resistance/higher current?).

[acapella8]

Is there a way that I can troubleshoot the Bosch CD?

[Howard M]

Do a search. I'm sure there is a check-out procedure in the archives.

[Early_S_Man]

MSD coils, at least the ones intended to be used on their own version of CDI, are compatible with Bosch CDI units, since the specs, i.e., turns ratio and primary resistance, are similar.

Documentation for the 6-pin Bosch CDI can be found in this thread:

6-pin SC/Turbo CDI unit repair documentation

Does the Bosch CDI unit whine or hum when power is on? If so, the inverter section is working, at least on the primary side ...

The tach movement implies that the trigger circuit is working, at least as far as T3 and D8! What we don't know about is the SCR and its' trigger, T4.

If the bottom cover is removed ... a certain amount of troubleshooting can be done with the CDI unit on a bench and connected to the car via a 6-pin extension cable consisting of four 18 ga wires and a piece of coax cable, such as RG-58 ... with six male Fastons on one end and six female Fastons on the other.