Sometimes there's spark, sometimes not.

[TripleBlackGator]

My cousin has a 383 1970 road runner. It has always started even after sitting for long periods of time. Now it wants to fire sometimes and sometimes it doesn't. The wiring harness is original and in good shape. The only cutting that was done was to add a Mopar Performance electronic ignition kit. That was done years ago and never hic-cupped. We found that when it has one of it's fits of not starting there is no spark coming out of the coil. We tried the stocker, an MSD Blaster, and an Accel. They all worked fine somedays but each failed to put out a spark on other days as well so we are ruling out a bad coil. It has a new ballast, and a new voltage regulator. Cleaning and tightening all electrical connections is no help. Kinda out of ideas right now. What would cause an intermittent spark from the coil? Any ideas?

[71_deputy]

check all grounds to the engine/ battery

[Plumcrazy]

Next time it won't start check the resistance thru the distributor pick up.
I can't remember off hand what it should be but I'm thinking its 500 to 1000 ohms.   
If you have no continuity at all thru it that's the problem.

[TripleBlackGator]

Next time it won't start check the resistance thru the distributor pick up.
I can't remember off hand what it should be but I'm thinking its 500 to 1000 ohms.   
If you have no continuity at all thru it that's the problem.

I need a more simplified explanation of the "distributor pick up". Your also saying resistance and then continuity. Which is it? I know continuity but not resistance. I do have a volt meter but I am a better mechanic than electrician. That's why I am asking in this section of the forum. Pretend I know nothing about the electrical system. You won't be far off. 

[Plumcrazy]

Next time it won't start check the resistance thru the distributor pick up.
I can't remember off hand what it should be but I'm thinking its 500 to 1000 ohms.   
If you have no continuity at all thru it that's the problem.

I need a more simplified explanation of the "distributor pick up". Your also saying resistance and then continuity. Which is it? I know continuity but not resistance. I do have a volt meter but I am a better mechanic than electrician. That's why I am asking in this section of the forum. Pretend I know nothing about the electrical system. You won't be far off. 

The distributor pick up is the electrical component inside the distributor.  The two wires that come out of the distributor go to it.
You will have to test it while the problem is occuring.  You will need an ohm meter,they're not that expensive.

Unplug the two wire connector that comes out of the distributor and touch the two meter leads to the two terminals.  It will show you a resitance reading if the pick up has a complete circuit (continuity).   If the pickup has no continuity the ohm meter will give you the same reading as if you turned it on and did not touch the test probes to anything,not even each other.

[TripleBlackGator]

Next time it won't start check the resistance thru the distributor pick up.
I can't remember off hand what it should be but I'm thinking its 500 to 1000 ohms.   
If you have no continuity at all thru it that's the problem.

I need a more simplified explanation of the "distributor pick up". Your also saying resistance and then continuity. Which is it? I know continuity but not resistance. I do have a volt meter but I am a better mechanic than electrician. That's why I am asking in this section of the forum. Pretend I know nothing about the electrical system. You won't be far off. 

The distributor pick up is the electrical component inside the distributor.  The two wires that come out of the distributor go to it.
You will have to test it while the problem is occuring.  You will need an ohm meter,they're not that expensive.

Unplug the two wire connector that comes out of the distributor and touch the two meter leads to the two terminals.  It will show you a resitance reading if the pick up has a complete circuit (continuity).   If the pickup has no continuity the ohm meter will give you the same reading as if you turned it on and did not touch the test probes to anything,not even each other.

Ok easy enough. Now, Is this with the key on? Cranking? Or just with the key off? Also, The reading should be 500/1000 ohms? If so, then what? If nothing like you said then what? How far back does the circuit go? Past the coil? Where? Like I said. I'm no electrician as you can tell.

I'll check back later this evening. Thanks. 

[Plumcrazy]

It doesn't matter if the key is on or not because you will have the connector to the distributor unplugged.
BUT!  you must be checking it while the problem is happening.  If the car won't start and the resistance is okay then you have eliminated the pick up from the list of suspects.

BTW I found the spec for the resistance thru the dist pick up, it's 150 to 900 ohms.

As you are finding out, intermittant electrical problems can be very difficult and time consuming to diagnose.  Sometimes you have to start substituting known good components to narrow down the problem.   Even if something doesn't fix it, you have eliminated one more possability

Other possabilities are a bad ECU, coil, wiring. 

[warlock]

If you swapped to electronic ignition, change the ECU, or be sure that it is grounded well. I always carry a spare anyway because they have gone south before. In my experience a bad ECU or a bad ground at the ECU usually causes an intermittent spark. Although I once had a bad wire in the distributor where the pickup wires exit out of the distributor. My $.02

You could also call the Mopar Performance Tech hotline at: 313-853-7290, Monday through Friday, 9:00 am - 12:00, and 1:00 PM - 5:00 PM, EST.

[TripleBlackGator]

Thanks guys. We will try your suggestions this weekend. My cousin and I are pretty busy during the week. 

[74440]

I am experiencing almost the same problem - just got a 400 in a '73 w/ OEM electronic ignition.  The last time I ran it, everything was fine - until it died.  After cracking for a bit I checked and didn't have any spark.  Today I was at it again and after a bit of cranking (no start or fire) I found that I still didn't have spark.  I messed with the wire harness (I just refurbished a lot of it) and, after trying another ballast & control box (no help) I started getting spark again (don't know why).  Now the car runs but only with the ignition switch not fully returned to "run" (I know I have a problem in the ignition switch).  Problem is that it will now run "for a bit' with the key in "run" and then it quickly dies out.  I have jumped the ballast and everthing works fine (feeding 12V to the coil).  I am running an old 140001 Accel super coil and don't have the "additional" resistor in line.  I am wondering if running this coil, without the extra resistor, can make the dual ballast overheat and cause voltage loss to the coil.  My feeling is that an additional resistor would only make the voltage even lower at the coil - already seem to be the problem.  Does anyone know if running the higher voltage to the coil (still retaining the resistor in-line to the ignition module) causes problems for the module?  The strange this is, this car ran just fine (so it seemed) with a 318 and the same coil and harness (never had the extra resistor).

[Nacho-RT74]

as I have stated on earliers topics, I have found at my car oftenly that problem is loosen ecu plug or dist plug

[Chryco Psycho]

the dist pick up  should be around 40 ohms resistance
ECU could be a problem, make sure it is properly grounded, make sure all the connectors are clean with no corrosion , di-electric grease will help keep them from corroding

[Nacho-RT74]

the dist pick up  should be around 40 ohms resistance
ECU could ba problem make sure all the connectors are clean with no corrosion , di-electric grease will help keep them from corroding

Haynes manual states from 150 to 900 Ohms... but maybe on performance picks ups is different dunno.

Usually mine is around 250-290 as far I remember