Low voltage at coil

[JG1966]

Hey guys. 1972 RR with 340 and mopar electronic ignition (blue box) and MSD coil. Long story short, I have a MSD Blaster 2 coil that has served me perfectly for nearly 30 years. Two days ago, I decided to install a Blaster SS coil that I bought on sale that had sat on my work bench for two years. After install, car idled like crap and tach was bouncing around. I checked voltage at coil positive with key on and got 3.4 volts. Called MSD and guy told me, "That's a low resistance coil and it doesn't work well with Mopar ignition. Put back on the Blaster 2." I wish the first MSD guy had told me that when I called two days ago before the initial install! So I put back on my trusty Blaster 2 and I'm still getting low voltage. 3.7 with key on, and 6.3 with engine running. I swapped out my blue ignition box for an orange box (which I admit I'm not positive is good) and got virtually the same numbers. The two-pin ballast is showing 1.4 ohms, the ECU is definitely grounded (.04'voltage drop). Two things are strange. I'm getting 11.6 volts on two wires going to the ECU when unplugged with key on -- the blue wlre from the ballast and the black wire from the coil negative. I thought only one wire powered the ECU. When I unplug the ECU, I get 11.6
volts at coil +, if that makes a difference. The only thing I changed during the install of the Blaster SS is I had to cut and lengthen two wires (the blue wire from ECU to ballast and the black wire from ignition to ballast) because I had to move the ballast a couple inches. I'm getting 11.6 volts into the ECU but only 6 at the coil. Is it possible the Blaster SS cooked my ECU? Can a ballast resister read 1.4 ohms and still be bad? Any help is greatly appreciated

 

[Geoff 2]

Is that the E core coil, #8207? I think it is quite possible that the extra current the coil was drawing has damaged the ECU. If it is damaged, any voltage readings are probably suspect.
If you have the #8207, now would be a good time to convert to a 4 pin HEI module. No bal res reqd, you get a more powrful spark & cleaner look in the engine bay. Wiring pics are on the web.

 

[JG1966]

Is that the E core coil, #8207? I think it is quite possible that the extra current the coil was drawing has damaged the ECU. If it is damaged, any voltage readings are probably suspect.
If you have the #8207, now would be a good time to convert to a 4 pin HEI module. No bal res reqd, you get a more powrful spark & cleaner look in the engine bay. Wiring pics are on the web.

Yes Geoff, it was the #8207. I put back in the Blaster 2 and I'm getting rid of the 8207. I went through the connections and my tach is no longer jumping around and my idle is back to normal. I'm still only getting about 6 volts at coil + with the car running (and only 8.8v when I start the car) but she's running and idling well. I have voltage drop that I'm trying to track down and fix. I'm also not certain I'm running the correct ballast (1.4 ohm) for a Blaster 2.