1970 Roadrunner isn't Roadrunnering

Neighbor's 70 Roadrunner isn't road running very well. The symptom is that the wire from the coil gives one single spark per try at starting. Each time he turns the key he gets one spark from the coil. Starter keeps turning over the engine but no fire.
We tried swapping out another coil he had sitting around and got the same single spark.
He has two pos and two neg wires connected to the coil.
Dark neg wire goes into what I'd call the wiring harness into the firewall.

Here it is first joining on one side of the pigtail, then here it is going into this slot on the harness, top row, second from the left:

Light blue with a green stripe goes to nothing. It terminates at some end he said has never been connected.

One positive wire goes to the side of the Edelbrock carb.

The other is a somewhat thicker purple color (it's spliced from one color to that purple) and goes somewhere into a taped bundle of cables -- and is one of the four purple wires -- either into what he's calling the OEM voltage regulator on the right or the other device just to the left of it. Or somewhere else and we just lost track of it.

Interestingly, when I tapped on that there was a white powder from the back. He doesn't strike me as the kind to do cocaine, so my second estimate was that it looked like the white powder you get from battery corrosion. We pulled it off the firewall and while there was a bunch behind there, it was in between this piece and the painted firewall.

Any guesses? I think it's a 393 or 383. I don't know MOPARs well enough, sadly.

It died the other day when he went to goose it at a light just around the corner.

Also, he has a '69 RoadRunner dash for sale. As long as I was snapping pictures I thought I'd throw that in there. PM me if interested. It appears to have a bullet hole in it...

It’s been over 15 years since I’ve owned a mopar but I believe the white piece your talking about is the ballast resistor which if I remember right do crap out. I don’t remember how to test it off my head but I’m sure a quick google search will yield you with a way. The ignition systems if stock are pretty basic so yet again I’d do a google search. Should take you 5 minutes with a multimeter to nail down the problem. 

Without being there to look at things and check with a meter I'm gonna guess ballast resistor. The white ceramic piece on the left side of your pic with screw in center. Back in the day we all kept a spare in the glove box of Chrysler products.  Kinda like keeping a DME relay in a Porsche or an ignition module in a car with GM HEI.

Mount the coil vertical. Only certain ones can be mounted horizontal. And I'd replace the one currently in the car with a new one.

That RR has had electronic ignition swapped into it at some point.   I wouldn't try to reinvent the wheel at this point, because it ran before.  The item to the left of the voltage regulator is the ballast resistor.   Pull the plugs off that, and make sure you have continuity across the top two terminals, and also across the bottom two.  (there will be resistance across each, and different values, as well, but it's been years, and I don't remember how many ohms each one is anymore.  Just as long as they aren't open, you should be okay)

Next, make sure all of those butt splices are okay.  I would solder them, myself.  Make sure there is a good ground between the ECU and the rest of the car, including the engine block (the ECU in this one is the orange thing in the 6th photo named, surprisingly enough the "Orange Box".   I really don't like the look of the wire that is being used as a ground strap between the back of the engine and the voltage regulator- I usually use a stainless braided strap from a '70s through '90s MoPar, myself.   

Check for wires that are hot, pull the cap, and make sure the rotor is turning, and not damaged, and check the center button n the cap.    

There's more, but that's a start.

 

Noid light on the primary side to determine continued voltage in?

With a ballast resistor you have two power sources to the coil. One is 12 volts from the key while cranking and when you let go it switches to the lower voltage from the ballast resistor circuit. Possible you have spark when cranking, but not when you release the key.

First thing I would do is use a wire with a pair of alligator clips and jump 12 volts straight to the coil and give her a crank. 

If it starts, then I would grab a voltmeter and start looking for where the voltage is failing to report for duty. 

If it does not start, then I would go looking for a problem on the ground side of the ignition.

It's been forever - does the 12V when cranking come from the ignition switch or does it come from the starter?

I've seen a few no spark when cranking caused by the wire on the starter falling off.

The single spark cements this as the issue.  Remember that ignition coils wire when you are NOT powered up.  So key on, the coil energizes, when you crank, it de-energizes the first time the breaker points (or electronic equivalent) open, and fires a spark, but now since there is no voltage on the +ve side of the coil, no more spark.

A jumper wire from pattery positive to coil positive will confirm this.  Yes it's not good for long term ignition life when a ballast resistor is assumed, but it WILL allow you to run it for a few seconds to verify everything else works.  Assuming you haven't flooded it by now.

Thanks all, I don’t think the neighbor has internet so I’ll print these off for him and bring it over for him to try. I’ll let y’all know when we get it figured out 

The only thing that fails is the ballast resistor on a Chrysler electronic ignition.

In fact the resistor fails so often I get a long screw and put 2 resistors on it so I can just plug in a new one when there is a failure.

In reply to bentwrench :

Don't forget the ground for the ignition module... although this car does not look rusty enough for that to be a problem.  (Or rusty at all)

One of the guys I used to work for was a gearhead in the 60s and he joked that instead of dipping their bodies in primer, Chrysler used to dip their bodies in saltwater before paint.

Knurled. said:

One of the guys I used to work for was a gearhead in the 60s and he joked that instead of dipping their bodies in primer, Chrysler used to dip their bodies in saltwater before paint.

Hahahahahahahahaha!

Does an electronic ignition like ballast resistors ?

If it's just a drop in electronic ignition I would go buy a set of stock points , get it to start on them and then decide if you want to fight with the electronic ignition.

In reply to californiamilleghia :

Mopar electronic ignitions did.

If it has electronic ignition, couldn't you get rid of the ballast resistor all together? Wasn't the purpose of those to keep from burning up breaker points?

In reply to ross2004 :

Chrysler igniton needed it, for whatever Mopar reason.

Looks like a Pertronix coil.  If that is the electronic ignition on there, they do go bad and give similar symptoms to what you describe.  Pertronix replaces the points.  I dig the Plum Crazy color paint jobs

It's been a minute since I've seen an old Mopar let alone work on one, I had a 70 superbee . I'll also vote for bad coil or bad blasting resistor. 

Now is it a pistol grip four speed or slushbox ? 

Burnout pictures will let us know it's back to roadrunning.

Guy I got my 914 from was a Mopar guy.  He had a 1970 hemi Roadrunner convertible.  It had a 383 in it when he got it, rust free and straight, trashed interior and top.  Took him 10 years to get it together, right motor and radiator, new top and interior, original paint, light blue metallic.  He bought a house when he sold it.  It was not as quick as his 440 6 pack Barracuda, which had stupid short gears in it and would lift the front tires when launched with alacrity.

It was the ballast resistor, gentlemen. I was at work but he came over pleased as punch and told my wife and kids :)

Without pictures, it isn't fixed.  lol

And your friend did buy 2 ballast resistors, didn't he?

By the way, I noticed that the car has 2 ignition control units.  The silver box is an aftermarket unit and the orange one looks like a performance replacement unit.  Go with the orange unit.

In reply to noddaz :

Very true! I will present that point to him

and I’ll pass along the note about the orange unit. I’m not very familiar with it so hopefully it will all make sense when I point it out to him

P3PPY said:

It was the ballast resistor, gentlemen. I was at work but he came over pleased as punch and told my wife and kids :)

Nice to guess correctly! Thanks for letting us know.

Meanwhile, tell him to install the coil vertical or that'll be his next issue. Only certain coils can be used horizontal.