Okay, my MSD6AL which worked perfectly for two years decided to get funky on my 89 RSconvt ZZ4TPI. I sent it back to MSD and they fixed one small part inside for no charge. I put it back on the car, same problem. I swapped the MSD over to my stock 92 Z28 convt 305 TPI, worked perfectly, no hesitation. So I swapped out the following from my 92 Z28 to the ZZ4TPI to try and eliminate the hesitation.
Cap, Rotor, ignition module, coil, distributor, coil wire pigtail from the ignition module to the coil. I put on new plug wires yesterday, no joy. The ZZ4TPI has a new AC Delco ignition module and O2 sensor, No abnormal readings on the Autoxray, though normally my BL is 108 ( I know, computer is pulling fuel) but now it's missing and showing a 114 BL. I have new SVO #24 injectors. Pulse width seems good, no knock retard under exceleration. Plugs are new AC Delco R44LTS. The ZZ4 cam with MR43LTS, which are Marine application plugs. Could I have too hot a plug? Do I need to step down to a R42LTS? I am really baffled. I have a $172 6AL box and a $100 timing controller I cannot use. The car is definately stronger with the MSD. Any ideas?
Fuel pressure gage says all is well in that department. I also plugged the MSD directly to 12volt battery and good ground to rule out a bad power source.
Thanks


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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

The MSD runs off the pickup coil in the distributor, what sorta shape is it in?

 

Madmax,
I swapped two different coils into the car. Including the one off my 92 Z28 convt (the car the MSD box works perfectly on). I thought perhaps the coil was too weak for the MSD also but I doubt two coils would be bad.

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Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

 

not the coil, the pick-up coil. its inside the distributor.

 

Oh, the distributor in the car has under 40K on it. I also swapped that once.

However I think I fixed it! I clean up the plugs and found a few exhaust leaks, #8 header tube and the header to y-pipe connections. I was pulling plug wires one at a time trying to find my dead solid miss. When I pulled #8, spark shot out of the bottom of the coil wire on the coil and grounded to the metal frame that holds the coil. I remembered my 92 Z28 had a rubber gasket between the coil bracket and the mounting bracket. The ZZ4TPI motor did not have this so I added one. ( I understand the two 10mm bolts holding the coil to the bracket probably still provides ground but I replaced it anyway). I also replaced the coil wire with the shortest one I could make. Problem solved. NO more miss and the MSD box works perfectly! After several months of trying to track this down I'm very pleased.

------------------
Rob P
89RSconvtZZ4TPI Edelbrock Intake
SLP Dual Cold Air Intake 1 5/8" Headers Semi-Siamesed Runners, IROC
suspension, alum shaft. Numerous mods.
92Z28convt5spd (stock)
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

[This message has been edited by Rob P (edited September 16, 2001).]