Cranks but won't start

[dmc8163]

My car has a Mopar Performance 426 and an MP electronic ignition (orange box). The car will crank but not start 99% of the time. Like now for example. For over a year I, and two professional mechanics, haven't been able to find the problem. We literally chased every wire. The engine harness is YearOne and the main harness is OEM. Every electrical component has been changed at least twice and a new MP distributor in on order. What could be causing this problem? Today I focused on the 4-prong ballast resister. With the key in the run position three of the four connections show 11 volts. The fourth, the brown wire to the ignition switch connector, tests 6 Volts. Where the brown wire meets the bulkhead connector both sides test 6 volts. In the run position both terminals of the coil test at 11 volts. Is the 6 Volt brown wire to the ballast resister normal? Would switching to a 2-prong ballast resistor help? Dave

 

[burdar]

With the yellow wire pulled off the starter relay, check for power at the + side of the coil with the key in the start and run positions. If no power, check the brown wire at the bulkhead and at the base of the steering column. If you are good there, take a spare distributor, and plug it into the engine harness. Hold the dist end of the coil wire 1/4" from ground(coil bracket works) and spin the distributor. Do you have spark? If not, try another ECU. If you have spark, double check that the reluctor gap is set to .008.

 

[dmc8163]

Thank you. I'll follow your instructions asap and let you know.

 

[RzeroB]

Hi there. Had a similar problem years ago and it was related to a ground. The ECU case is the ground for the ECU and normally gets a good ground thru the attachment screws to the cowl. Your ECU might not be getting a good reliable ground to the cowl. Try a jumper ground from the ECU mount screw to the engine to ensure you have a good ground and see if that helps.

 

[dmc8163]

Hi, Im sorry for the delay. My ballast resister is not wired coorectly and I seem to be incapable of getting a 2 or 4 prong BR to work despite dozens of wireing diagrams. Right now I'm trying a 2 prong with a 4 post ECU. It'n not working. on the left side I have a heavy brown wire and the blue coil wire. On the right side I have the blue/yellow wire from the ECU and a blue wire that I think goes to the voltage regulator. No joy and there is no power to either side of the BR with the key in the run position. Sigh..........it's killing me. Dave

 

[burdar]

Start at the ignition switch and work forward. Do you have power on both sides of the ignition switch connector at the base of the steering column? The red wire is constant power in. The black wire is 12v out with the key on. The blue wire is ignition in the "run" position. Brown is ignition in the "start" position. Yellow is accessory.

Then move to the bulkhead connector. Do you have power on both sides of the bulkhead?

 

[Chryco Psycho]

you are wired correctly at the ballast , the blue wire to the VR should connect back to the firewall & through to the ign switch & should have 12v with Key on except in the start position

 

[dmc8163]

Can anyone tell me exactly what color wires go where on a 2 prong ballast resistor? The car is a '70 Challenger, MP 426 and MP electronic ignition. Thanks, Dave

 

[Chryco Psycho]

sure one end will have a dark blue 12v feed from the ign , the other end will have a brown wire start feed from ign & a blue or brown wire the the + coil terminal

 

[dmc8163]

Thank you to all of you helping me sort out this problem. After completing all the tests I decided that I needed to junk my new, albeit cut up, electronic ignition engine harness from Year1. I replaced it with an original, i.e. non-electronic, Year1 engine harness. Spliced the control wire into the feed wire and presto the car starts. Now, happily, I'm back here I started. On the road the engine routinely shuts down without warning and won't restart. I have run out of ideas and I'm beginning to think it may have something to do with the ignition switch. D

 

[Ridr]

Just remember with the four prong resister that in the start position you get 12volts, run position 6volts. Hope it helps.

 

[dmc8163]

Thank you. After the frustrating experience with the four prong I went with the two prong and it worked great.

Just remember with the four prong resister that in the start position you get 12volts, run position 6volts. Hope it helps.

 

[napaguy]

i am having same problem with my 72 challenger, thinking that amp gauge could be problem. getting ready to pull dash and use madelectric bypass for the amp gague. have found melted wire going from bulkhead to switch. won't know untill we get dash out, something that you might look at

 

[Chryco Psycho]

you can simply bypass the ammeter by connecting both wires to one post of the ammeter

 

[dmc8163]

Hi, everyone. Thank you for all your suggestions. I was unable to fix the problem and had to walk away from my very own "Christine" to avoid blowing her (or me) up. Since my last post I have replaced the original dash harness with a new Year1 harness. I now have a new Year1 engine and dash harness. I also have a new voltage regulator, ballast resistor (2-prong), Mopar Orange box, bulkhead connectors, and Mopar Performance Distributor. And...you guessed it----cranks but won 't start. I purchased and installed a restored OE steering column which presumably has a new ignition switch (but I can’t verify). I have the following voltages:
Battery 13v
Key On
Ballast resistor*- Green/yellow wire & Blue wire = 6.7v
Blue/Brown wires = 1.2v
Resistance = 0
Continuity = yes
*During testing became too hot to handle (this is a first)
Voltage Regulator Blue wire = 11.6v
Green wire = 11.6v
Orange Box Grey/yellow wire = 11.6v
Black/yellow wire = 11.6v
All other wires = 0
Coil Positive+ = 6.7v
Negative- = 1.2v
Bulkhead Connector Brown wire = 6.7v
Blue/white wire = 11.3v
Key Start
Bulkhead Brown wire = 9v
Bulkhead blue/white wire = 11.5v
Coil positive = 9v
Coil negative = 2/3v
Once again I turned to those with the expertise to solve this problem. Hopefully, this provides more information to consider. You remember what happened to the original Christine right? -------

 

[Chryco Psycho]

Well do you get spark if you hold the coil near ground while cranking ?
If you have a short inside the tack the coil will ground out & prevent any spark so possibly disconnecting the tach signal wire from the coil will allow the coil to create a spark

 

[dmc8163]

Chryco Psycho, you are a genius. I’m including you in my personal small select group of hero’s. I removed the tach wire and got spark. The engine started. It’s running very rough but it is running. As a test I touched the tach wire to the negative coil terminal. I thought that would shut down the engine. I was surprised when it didn’t kill the engine. There was movement in the tach when I did this. Why didn’t it kill the spark? If I left it connected would it have eventually killed the engine? Many thanks, Dave

Well do you get spark if you hold the coil near ground while cranking ?
If you have a short inside the tack the coil will ground out & prevent any spark so possibly disconnecting the tach signal wire from the coil will allow the coil to create a spark

 

[Chryco Psycho]

Awesome , , I figured after everything you had changed it could be in the Tach , lets just say I have been around a while LOL .
Maybe there is a problem at the coil connection & the wire was grounding there against to coil body or something & removing it fixed the short to ground so when you reconnected the wire the short didn't contact again so it didn't shut down the engine but at least now you know where to look for the problem !!

 

[dmc8163]

Absolutely. But I don't call this car Christine for nothing. I have been working hard to get her to run reliably for three years. She has repeatedly decided to stop running for no apparent reason. I'm hoping that this will be her final tantrum but I have to keep her history in mind. :icon_lol: Thanks again, Dave

Awesome , , I figured after everything you had changed it could be in the Tach , lets just say I have been around a while LOL .
Maybe there is a problem at the coil connection & the wire was grounding there against to coil body or something & removing it fixed the short to ground so when you reconnected the wire the short didn't contact again so it didn't shut down the engine but at least now you know where to look for the problem !!

 

[Chryco Psycho]

Christine was opposite , she would run no matter what they did to her !