No clue, please help

For your extinguisher may I suggest

https://coldfiretactical.com/

Spendy, but it wont mess up finishes and everything else like a regular extinguisher will.

You can get it on Amazon etc

Aeronet said:

'73 Charger, 400, Thermoquad, 727, factory electronic ignition.
I start car and drive to work. After work I start car and drive home. On the way home I stop at store, park car, shut it off. I come out of store and car won't start.
The drive to work is ~20 mikes of mostly highway and takes about 30 minutes and I'm stopping after I've driven nearly to my house.
I've owned this car for twenty years and it has never done this. It's not the ECU or the coil (I've used two different ECUs and three different coils all of which are known good). I changed both of those components and it still won't start. After a couple of hours the car will finally fire up.
Anybody know what could cause this? I sure don't.

Click to expand...

Check your grounding wires charge if your battery and look at what is voltage being out out by generator

Aeronet said:

I've also had trouble with the blower motor switch. The previous owner had by-passed it. I hooked it up again. Burned it twice. I by-passed it again because one more burn up and the switch is toast. I could smell it burning.

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I'll bet you a beer it is already damaged. Start shopping, or get ready to use your extinguisher.

The ballast resistor is bypassed for starting, and is used to "cool down" the spark for running. Chrysler had two systems which are functionally identical. One electronic ignition unit has a 5-wire connection. This one has two external resistors in a single package on the firewall. One is called the compensation resistor, which is actually the ballast resistor. It is in series with the coil 12v side, and actually varies the heat of the spark some based on rpm. The other is called auxiliary resistor. This resistor connects to pin 3 on the electronic ign. unit. The other system has a 4-wire connection, and the auxliary resistor is built into the ECU. These external resistors are wirewound resistors encapsulated in ceramic. Sometimes the leads running out to the terminals break, and the connection becomes intermittent. Ignition won't spark. But you said you've swapped out the ECU and the resistor, so rule them out. Check to make sure you're not vapor locked. Get the car warmed up, then shut it off in your driveway or garage. Loosen a plug that's easy to get out quick, put the wire back on. Wait the usual amount of time, and crank it with throttle open wide for a few seconds. Quickly get the plug out and see if it's wet. Ground the plug electrode to the engine and crank. See if there's spark. Might need a helper.

Also, the pickup coil in the distributor could be suspect. Not easy to check without the right equipment. Not easy to get at bare wires. If you're handy with electrical, you could stick a couple thin wires into the connector, attach a voltmeter, and see if the meter is blipping while cranking.

Remote, but possible if the wiring harness is old and brittle - a broken connection that is heat sensitive. I had this recently on the temp gage. You might try popping the hood when you shut it off to see if it makes a difference. Good luck.

I'm still working on solving this mystery. I'm going to do a voltage drop check this weekend. If I shut it off after an 30 minute highway drive and immediately try to start it, it starts. It's when I let it sit for a few minutes that the trouble begins.
I am going to pin point exactly what the problem is so I will know it is solved.
I haven't explored any fuel related issues. It could be vapor lock, I just don't see how since in the twenty years I've owned it I never had a vapor lock issue.
I'll update later.

I'm going with your bulkhead. Sounds like thermal expansion is causing intermittent voltage to your br.
Once those terminals have heated up several times, each time it will get progressively worse until it melts down
Get a jumper wire and run from the br into the car and splice in ahead of the bulkhead and test it making sure to get the engine bay hot enough and enough load going through the connector.

Still working on it. I think I can safely say it's not fuel related. Decided to start from the beginning and looked at the troubleshooting section in my Haynes manual. Vent tubes clogged? Float too high? Distributor pickup coil gone bad? Bad ground? Dirty air filter?
I took the carb off and noticed that the metering rod wells were leaking, a lot. Ah ha! Thought I. I had rebuilt the carb last fall and used regular 5 minute epoxy on the wells. I put my other Thermoquad (had it for decades and used it on this car. It is known good) on and thought I was good to go. Well, I wasn't. Sat at O'Reillys for a couple of hours. I bought a spark tester while there. Here's irony for you. I connected the tester to the #1 plug wire, turned key to run, and jumped the starter relay. The car fired up. Took the tester off and tried again. No fire. Hooked up tester again and no spark.
I'm in the process of replacing the distributor coil pickup. I'll know if that is the problem tomorrow.
I guess that, like the coil, a distrubutor pickup can ohm out good, but short when hot.

Aeronet said:

I guess that, like the coil, a distrubutor pickup can ohm out good, but short when hot.

Click to expand...

It's acting that way, isn't it? I had that problem once with a coil on a 318.

Demonic said:

It's acting that way, isn't it? I had that problem once with a coil on a 318.

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We shall see. I know it's not the coil. Only part I haven't swapped out is dist. pickup.

It was the distributor pickup. Changed it this morning and ran errands this afternoon without a problem.
So, a distributor pickup can have the correct ohm reading, but still short out when hot, just like an ignition coil.
Pain in the rear though it was I did find some problems that needed fixing.
Sometimes I think that car does stuff like this when it feels neglected and needs attention.
Well, thanks for the replies. All very helpful and I learned some things.