73 Roadrunner engine misfire, overheating and under dash electrical.

[MontanaMopar]

First off, I have a head injury and can forget some major stuff and have difficulty communicating. I also have to do this multiple times to get it right. However, I have owned the car since 1980 and know it very well.
The engine has a bad misfire and overheats. I have eliminated all of the typical causes under the hood.
It is currently running on a factory ignition box, new Mopar distributor with a lock plate set at 34 degrees and an MSD Blaster II coil. The engine is a factory .040 over low compression engine with a Hughes Whiplash cam, a custom Dynamic Converter that stalls at about 3,000 RPM. It has a new 26” brass/copper radiator, motorhome water pump, 906 stock reconditioned heads, short tube headers and a Mopar dual plane manifold with a QuikFuel 780 w/vacuum secondaries and 5.0 power valve.
I believe the problem to be in the electrical from the bulkhead connector back. I replaced the ignition switch wiring harness last winter, the starter relay and reverse lockout switch have also been tested and replaced.
I have intermittent trouble starting the car with the key. I recently re-connected the seatbelt switches. I believe that all of the trouble comes down to something in the electrical system from the firewall bulkhead back.
I have tried multiple distributors, ignition systems, MSD Streetfire, points, plugs and wires, currently running the FireCore wires. I have checked the cam centerline.
I am at a loss. No matter what I do I cannot get the car to run right.

 

[Gus chiggins]

First off, I have a head injury and can forget some major stuff and have difficulty communicating. I also have to do this multiple times to get it right. However, I have owned the car since 1980 and know it very well.
The engine has a bad misfire and overheats. I have eliminated all of the typical causes under the hood.
It is currently running on a factory ignition box, new Mopar distributor with a lock plate set at 34 degrees and an MSD Blaster II coil. The engine is a factory .040 over low compression engine with a Hughes Whiplash cam, a custom Dynamic Converter that stalls at about 3,000 RPM. It has a new 26” brass/copper radiator, motorhome water pump, 906 stock reconditioned heads, short tube headers and a Mopar dual plane manifold with a QuikFuel 780 w/vacuum secondaries and 5.0 power valve.
I believe the problem to be in the electrical from the bulkhead connector back. I replaced the ignition switch wiring harness last winter, the starter relay and reverse lockout switch have also been tested and replaced.
I have intermittent trouble starting the car with the key. I recently re-connected the seatbelt switches. I believe that all of the trouble comes down to something in the electrical system from the firewall bulkhead back.
I have tried multiple distributors, ignition systems, MSD Streetfire, points, plugs and wires, currently running the FireCore wires. I have checked the cam centerline.
I am at a loss. No matter what I do I cannot get the car to run right.

View attachment 1533199

You might want to consider using a stock coil.

 

[MontanaMopar]

You might want to consider using a stock coil.

Thanks Gus, but I did, this thing is a nightmare.

 

[Curiousyellow71]

Can you explain your misfire better? What the misfire sounds like over the rpms? Intermittent or all the time? Did the Miss start suddenly or been this way since the engine was installed?

Overheating issue change at all with anything you've done? Where is your timing set?

Maybe hot wire the ignition and see if it eliminates anything?

 

[MontanaMopar]

The misfire is across all cylinders, it has been there with various different cylinder heads, it does it most of the time, at higher rpm’s under wide open throttle it seems to get better, but with Flowmaster 40’s it can be hard to tell. Timing has been set all across the board but is now at 34 total. I have tried isolating the msd from the rest of the car wiring but damn it I just can’t remember right now wat all of the problems were. I remember it still overheating and I believe that the miss was still there. The overheating hasn’t really changed much with changes.

 

[Curiousyellow71]

Anyway to post a video of it missing?

Initial thought pull plug and Verify TDC for #1 and make sure the distributor is not 180 out.

 

[MontanaMopar]

No video right now other than at idle and I don’t think that the site will let me upload video. One thing I forgot to mention is that the tach will jump around. The instrument cluster was restored about five years ago by Redline and upgraded to modern ignition systems. These are the shorty plugs that I recently removed, I replaced them with NGK standard plugs. At the time I thought that the plug wire boots were too long. Now that I’m running short tube headers I no longer need the short plugs.

 

[70chall440]

Based on what you wrote my take is that you are dealing with several problems simultaneously.

1. the overheating: if it has always overheated using the same components on different engines then your components are suspect. First off I would flush the crap out of that system and make sure it flows well. Second I would change the T-stat just because and then see what happens. I once had a 440 that would overheat rapidly, tried everything but to no avail, flushed it out and dog food came out of the water jackets... seems that this engine had sat in a barn for awhile after being rebuilt and mice took of residence. Also, I would have that radiator hot tanked or replaced with another to see if there is a change.

2. the electrical issue: sounds like your ignition switch or perhaps one of the connections is loose, however I would suspect a bad or loose ground/s.

3. the misfire: I agree that in order to get some help here we are going to need more details. Have you hooked up an external tach say on a timing light and rev'd it up and saw the misfire (rpm dropping momentarily)? Based on what you have said it sounds a little like you might have some arc'ing someplace on one or more wires but you should see evidence of that. You might try running it and turn the shop lights out to see if there are any stray sparks from the wires or boots. Other than that its going to be pretty hard to diagnose on a forum. How does the inside of the distributor cap look? Are you are sure the distributor is in good shape or doesn't have a bent shaft?

The spark plugs look a bit rich to me.

 

[MontanaMopar]

Thank you so much for your reply! First the engine is fresh, I knocked out every bit of flashing I could find on both the block and heads. I pressure washed the entire block and heads until all the water jackets ran clean. The radiator is new and cools just like the aluminum one I replaced. I have tried several thermostats and am currently running a high flow performance one with a bypass orifice.

You may have hit the nail on the head with the ignition switch. In my experience most electrical problems come down to a ground. The ground wire from the column to the dash is in good shape and secure.
I had major problems when replacing the ignition switch wiring harness. It’s entirely possible that I screwed up something with the installation. Very common for me these days.

The distributor is a new Mopar Performance one. I have checked the shaft and it spins true. I have tried different caps, rotors and wires. Right now everything is new. The contact at the center of the cap is in good shape too.
I have not tried an external tach but I will check it with my timing light.

I have been very suspicious of the 1973 seat belt ignition lockout and the neutral safety switch. I am also suspicious of the wiring bulkhead at the firewall. I just had hand surgery making it very difficult to work on anything. My head injury doesn’t help me any either.

If anyone has had a mystery ignition problem similar to mine I would greatly appreciate hearing your story.

Thank you so much for your help!

P.S. you may recognize my car as I am originally from the Puyallup area and have raced it extensively at SIR.

 

[Curiousyellow71]

If you think this is a wiring issue run a hot wire to the ballast resister and see if the miss goes away. There are two schematics depending which ballast you have. Posted is the ballast w 4 connections. Also might check the air gap on the distributor. Both initial and advanced. Its suppose to be .008. Unfortunately a lot of new parts arent what they should be for quality.

 

[MontanaMopar]

If you think this is a wiring issue run a hot wire to the ballast resister and see if the miss goes away. There are two schematics depending which ballast you have. Posted is the ballast w 4 connections. Also might check the air gap on the distributor. Both initial and advanced. Its suppose to be .008. Unfortunately a lot of new parts arent what they should be for quality.


View attachment 1533525

Thank you for your reply! I believe I have tried that in the past but I’ll give it another shot. Right now I’m having an issue with even getting power out of the bulkhead. It must be the main power supply wire, normally the fuseable link, at the bulkhead. Just very difficult for me to get in there with my hands being messed up. I’m going to work on it some today, we’ll see!

 

[MontanaMopar]

Update:

I found that I was only getting 10.4 volts to the ballast resistor and 5.6 to the coil and 3.5 out of the coil. I did a little research and found that a MSD Blaster II coil handle 12 volts as long as you’re not using points. I am still skeptical of this, however I ran a wire from the battery, to a switch and then to the positive side of the coil. Car runs great! I know this is just a Bandaid until I narrow down the real problems.
Any advice?

 

[MontanaMopar]

Update:

I found that I was only getting 10.4 volts to the ballast resistor and 5.6 to the coil and 3.5 out of the coil. I did a little research and found that a MSD Blaster II coil handle 12 volts as long as you’re not using points. I am still skeptical of this, however I ran a wire from the battery, to a switch and then to the positive side of the coil. Car runs great! I know this is just a Bandaid until I narrow down the real problems.
Any advice?

So the impossible just happened. I started the car this morning and is was running bad again. When I got to the gas station I turned the key to the off position and the engine shut off without turning off the bypass switch! The negative side of the coil is still connected to the factory wiring. WTF?! Any help would be greatly appreciated!!!

 

[Curiousyellow71]

One thought...make sure the ground is connected from the body to the engine.

Are you going directly to the battery for your hot wire? The miss being back and the key shutting off are both signs the hot wire is not making a good connection....somewhere.

Because just like your thinking...key should not be turning engine on/off if bypassed.

 

[4vnut]

I think you need to do some serious wiring harness investigations/cleaning. When I had my wiring harness (wh) in my hand, during the restoration, I dipped the terminal ends in muriatic acid for just a few seconds. Then flushed with plenty of water, lightly brushed the blades with small brass wire brush, applied dielectric grease and they looked like new. Cleaned all the wh's with this method. 24 years later the car hasn't had any electrical problems. We don't need any electrical gremlins ruining our cruise's when the connections can be much improved.

 

[MontanaMopar]

One thought...make sure the ground is connected from the body to the engine.

Are you going directly to the battery for your hot wire? The miss being back and the key shutting off are both signs the hot wire is not making a good connection....somewhere.

Because just like your thinking...key should not be turning engine on/off if bypassed.

Thanks once again. The engine has a good ground to the firewall. The switch goes directly from the battery to the coil.

 

[MontanaMopar]

I think you need to do some serious wiring harness investigations/cleaning. When I had my wiring harness (wh) in my hand, during the restoration, I dipped the terminal ends in muriatic acid for just a few seconds. Then flushed with plenty of water, lightly brushed the blades with small brass wire brush, applied dielectric grease and they looked like new. Cleaned all the wh's with this method. 24 years later the car hasn't had any electrical problems. We don't need any electrical gremlins ruining our cruise's when the connections can be much improved.

As much as I dread removing the wiring harnesses I. Think you are right. I did inspect and clean the under dash harness about rive or six years ago when I had the instrument cluster restored. Unfortunately with my head injury I can’t remember much of what I did. It sucks! I have done so many things and tried so many different combinations over the years it’s very easy for me to forget or get confused. I do take a lot of pictures and keep notes, but unfortunately I’m not consistent with it. I’m getting to a point where I’m very hesitant to do any major things to the car. It was down for six months over the winter last year, sitting outside no less, because I couldn’t get the steering column back together. Also I’m on a fixed income and can’t afford to pay a pro for much.

 

[Curiousyellow71]

When you went to the coil did you leave the factory wire hooked up? Try to unhook the wires at the ballast to the car and run a hot wire to the incoming side. I think perhaps your hot wiring is powering in "start" and not "run"....hot wire going to the coil. Look at post 10. I don't think your hot wire is correct and the key would still shut it off. It would have worked for points but not electronic.Not sure if it will get it, but worth a try.

I think you gave me a fat finger disagree on post #10.

 

[MontanaMopar]

When you went to the coil did you leave the factory wire hooked up? Try to unhook the wires at the ballast to the car and run a hot wire to the incoming side. I think perhaps your hot wiring is powering in "start" and not "run"....hot wire going to the coil. Look at post 10. I don't think your hot wire is correct and the key would still shut it off. It would have worked for points but not electronic.

I think you gave me a fat finger disagree on post #10.

I’ll give it a shot tomorrow, thank you more than you know!