Cuda No Start **UPDATE**

[chargerdon]

Okay, I have an update! I jumped a wire, from the battery to the positive side, of the coil, still no start, with turning the key. However, with the coil still jumped, and the key in the "run" position, it started, by jumping the starter relay.

I have had this same problem...Sometimes wont start with key, but with key on and jump the starter relay and she starts.   In my case the reason is that somewhere in the "start" wire lead to the ignition system i'm losing voltage.    Haven't been able to fully track down. 

My car is 74 challenger with the "stock" Mopar Electronic ignition system.   That system has a crazy flaw in its design.  When key is in crank/start position the ignition key does NOT send power on the "run" lead but only the crank lead.   It goes to the 4 post ballast resister right at the coil feed to give "hotter" coil for starting...i.e bypassing the ballast for the coil.  Great...but that means it goes thru the ballast to get to the ECU with its resistance meaning the ECU gets a lower voltage on crank than it does on run.   I have been told that if the voltage to the ECU falls below 9V then it wont fire the coil.    Thus the problem!!   

I tried putting a jumper wire across the coil side of the ballast resistor to eliminate the resistance.   That actually works, but, then the coil would be getting the full 14V of the alternator when engine is running and of course that would lead to it failing eventually.   I have thought about putting a diode in that jumper wire so that when running, it would prevent the coil from getting fed from that jumper.   Kinda sure that would work, but, im better off finding my voltage drop.

PS...testing this problem is ignition is easy...   simply put on a timing light...no light no fire from ecu to coil.   

[dodj]

 
floorit...This thing must be running by now?

[floorit426]

Yes, it is. I've been focusing on a couple of other small gremlins, but got it figured out, Friday. There was voltage to the ballast resistor, but none to the coil. It turns out that there was a bad connection, on the out lead, of the b.r. Thanks, for the reminder to update the story.