I drove the Challenger this morning and then shut it off. About 2 hours later, I went to restart it and it would not fire. It turned over fine and the battery was at full charge, but no spark at the end of the coil wire.
I changed coils and no spark. First coil back on.
I swapped ECU's and got a spark. I put the first ECU back on and got a spark. I then started the car and it idled fine but I am now worried about what caused the no spark. I now have the first set of coil/ECU back on and it started fine.
Something caused the no spark, but I am not sure what component is showing an intermitant problem.
Note: Non-ballast ignition system.

Thanks

iffy ground

yeah make sure it's making good contact somewhere on the bottom side

id check grounds,ballast reistor,ignition switch ive all these give the same result.

Thanks everyone.
I do have a ground on the frame for the ECU but I will move it from the firewall to in-between the ECU and the mounting bracket that mounts to the firewall.
This just seems weird because I have been running this system all Summer and not an ounce of a starting issue. I do not know why all of a sudden this starting happening. I will move the ground and see what happens.

Thanks again.

Run a dedicated ground to it, never have too many grounds

Check the bulkhead connectors..
After 40 years they get oxidized and need kleening.
Pop them part, wire brush the terminals kleen and coat with dialectric grease..


Just my $0.02...

Bulkhead connectors are clean with dialectric grease.

One thing that I noticed during these tests, when I swapped in the second ECU, I just layed it on the valve cover and then turned the motor over and noticed no spark. Then I realized what I did and then ran a pigtail ground from it to my ground source and then turned the key and found spark for the first time again.
This is proof that the ground to the ECU is very important. Since mine is currently grounded thru the mounting frame of the ECU and not the body of the ECU, then hopefully this is the problem.
But, I still can't think of a reason that I have run this setup all Summer as is, with no problems until now.

Note: Before this ECU swap, I had the ground at the body of the ECU, then when I swapped in the new ECU (non ballast setup), I moved the ground to the base of the mount bracket. I will keep the one at the base of the mount bracket and add a second at the body of the ECU.
Note 2: The picture is old but it shows the ECU mount bracket that I am referring too.

Could this be the connector or the harness causing the issue?

Thanks again.

Is there anything that comes to mind that I might need to check?
Brown wire?
Ballast bypass connection (ballast removed)?

Thanks

""The only change was the ECU & when you confirmed the ground the prob went away""

After replacing the first coil with a known good second coil, then I grabbed a second good ECU and laid it on the valve cover. Once I added a ground wire to the second ECU, that was when the voltage came back at the coil wire. Then I just moved the harness off of the second ECU back to the first ECU (which I never removed) and then I got spark from it again. This is why it does not make sense, unless I have an issue in the harness.

Would the pickup gap cause this? The last time that I checked it, I had it set at .008".
Thanks

air gap could cause this but i would like to think it would be all the time. i think plugging and unplugging the harness 'pushed' the ECU into making a ground. in looking at the pic, it appears your ECU is mounted on a bracket and the bracket is mounted to the firewall? if this is true clean up all the mounts and maybe put some of that grease between all the areas. i used to put stainless washers behind the box and scraped the firewall bare. now i use MSD so i don't have that problem anymore.

I added a ground wire to the ECU body mounting bolt and checked the one on the mounting bracket. I also removed the ECU connector and added dielectric grease and put it back on a little more snug than the last time.
Don told me to make sure of the reluctor gap so I pulled my dist and the gap was about .006". So I cleaned the connectors and restarted the car twice with no issues.
I did not see anything obvious so I will keep an eye on the issue.

Thanks to everyone for the replies.

""being paranoid about a potential breakdown is no fun & takes the fun out of it""

That is exactly what I was thinking Saturday when I finaly got it restarted but I did not know why. I was gun-shy to drive it until I had the time to investigate it. I hate that feeling.

Thanks Robert.

IT DID IT AGAIN!!

I drove the car twice this afternoon with no starting problems. I tried starting it again for the third drive and no start. So I pulled the coil wire and confirmed no spark to coil. This time the engine only sat for 10 minutes or so and then a no start. So I pulled the harness at the ECU and just put it back on and no spark at coil. I ran out of time but I will swap ECU's later to see if that it the issue.
This is exaclty what happened last time. It seems that after an hour or so of driving, something goes and it wont give a spark.

Thanks for listening (or reading )


Update:
I tried two hours later to check for spark at the coil and nothing. I was thinking that maybe something was getting hot. Then I swapped out the ECU and had major spark. Then I swapped back to the first ECU and found very minimal spark from the coil at start. It appears that the first ECU does not want to fire at startup.

Put the new ECU back on & if that takes care of it for several days w no probs give the 1st one a good toss against the wall (it'll make you feel better)

Have you checked the air gap on the reluctor & pick up coil... A weak pick up coil can also cause the issue...

Two weeks ago when this happened, I was directed to check the pickup gap. The gap was apx .006". I did not recheck it this time because swapping from ECU #1 to ECU #2 gave me spark again. Then swapping back from ECU #2 to ECU #1 gave me no spark again.
I am contacting the manufacturer today to try and get the #1 ECU replaced.
Note: #1 ECU is only about 4 months old. #2 ECU is about 4years old and it appears to be still going strong.

I would throw #1 ECU against the wall but I want my warranty.

Thanks