My old boat still has the original '74 318 with the first generation breakerless distributor. I've been having rough running/loss of power above 1200 rpm issues for a while. I've replaced every item in the system except the distributor and the pick up coil. I bought a replacement pick up coil but when I tried to adjust the air gap I could only get to 16 thou, spec is 8. I just need to file the slot a hair longer to get a bit more adjustment. Regardless the existing pick up coil tests ok.
I've noticed it seems to get worse after it's fully warmed up (10-15 min) and if I try to rev above 1200 rpm. It revs fine without a load in neutral. My normal cruising speed is 7.5 knots at 1800 rpm, and it's been up and cruising at 22 knots and 3200 rpm. I've also noticed the ballast resistor ceramic heatsink gets very hot to the touch, as does my new coil. I've rewired the ignition primary wiring and it seems ok, I thought I might have high resistance in the original wiring.
Is it normal for the ballast resistor (I've tested it) to heat up that much? And the coil too?

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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight

Is the coil internally resisted. I would verify it is not with an external resistor.

IMO I would convert the system to a MSD 6AL ignition system with an internally resisted coil utilizing the current pickup. I have never thought much of the "pray for spark" Chrysler ignition systems.

Don't have any useful advice except to say that I put a Pertronix aftermarket electronic ignition inside the standard points/condensor distributor in my MOPAR 413 and it worked great.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

No, it's normal for it to heat up like that. The ceramic block is most likely bad. It's less than $30 for another one.

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1987 560SL
85,000 miles

Also, if it has the ESCM (electronic spark control module) it may be on it's way out. I had a '78 Newport with the same engine and went through 4 of them before I pulled the dizzy out and replaced with the old point style dizzy. 20 years ago, the ESCM was around $400 apiece, but they may be cheaper now. You can pull it off and take it to NAPA and have it tested.

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1987 560SL
85,000 miles

MSD or check the MOPAR forums, there are many threads about converting your system to the GM HEI module (cheap) and bypassing the ballast resistor. PO had done the conversion on my old Power Wagon and it ran great.

Don't know how much the GM HEI costs but a Pertronix inside a standard MOPAR distributor runs about $75.

http://www.vintageperformance.com/retrorockets/chrysler.htm

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

Here is some info, there are many others.

Mopar HEI Conversion

I don't know how hot they are supposed to get, but the ballast resistor is (in)famous for burning out with no warning, and when it does the engine will stop immediately and it will strand you where you are. I used to carry at least (1) spare in the glove compartment.

See if you can measure the voltage across the coil and across the ballast resistor with the ignition on but the engine not running. I am guessing that they should be about equal, putting about 6V on the coil and the rest on the resistor.

Best of luck.

I always carried a spare as well. I also learned to carry spare dizzy cap and rotor button. If a dog pissed on the tire, the thing wouldn't start. I've had 4 different mopars with that family of engine in them, each suffered from the same problem...dizzy was in a bad spot on them.

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1987 560SL
85,000 miles

I know those engines quite well from my days at Chrysler. I cannot tell you how many times we had similar issues with a vehicle that simply would not run even though everything checked out fine.

The end result was always the GD ballast resistor. It deteriorates and won't provide the necessary current to the coil.

We even replaced several coils without any benefit.

If you want a quick test, run 12V directly to the coil and drive it. The coil normally runs on 6V but a quick test at 12V won't harm it. It starts on 12V and runs on 6V...........the job of the ballast resistor.

I would not bother with the voltage check as mentioned above. Proper voltage with the key on doesn't preclude a problem with the ballast resistor. You'd need to measure it under load and at high speeds.

Have you ever swapped out the Dist cap, I had a very similar probem in my 73 Road Rummer, Didnt run good under load once warmed up, I replaced the pickup, the coil, even the electronic ignition on the fire wall, (which in the end I wasnt mad because I upgraded to Mopar Performance parts), In the end it ended up being a very very small crack in the dist. cap, I couldn't see it until it started forming little electrical burn marks. replaced the cap and never had the problem again.
something to think about at least.

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Wow guys thanks for all the ideas. I just put a new ballast resistor and spark control unit in a couple of weeks ago, swapped back to the spare set when it didn't make a difference. I've tested the coil for resistance and it's in spec. I'll try a new cap and rotor this weekend and see if that makes a difference. I replaced it last year and it still looked fine.....

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Democracy dies in darkness, you have to kick at the darkness till it bleeds daylight

As weird as it sounds you might try a new set of plugs. I went through this and finally drug the thing to a shop with an ignition computer and they found that all my plugs were normal until the engine warmed up, then one expanded due to a crack in the body of the plug.

New plugs made everything OK.

And about the coil heating up... Yeah, they do that. Fiat 124's used to get so hot their coil came from the factory mounted on the fender in a heat sink. Bumping into one was not as bad as hitting an exhaust manifold or a hot radiator, but you knew you had bumped into something hot.

On a 360 I had same problem. Any time the vac' advance was hooked up it wouldn't run over 1000rpm...so ran it without vac' and was fine.

Next time I looked at it I found the reluctor teeth too far from pick-up head and it got wider with vacuum applied. Adjusted it to as close as possible but without touching, and it's been fine ever since. Gap has gotta be around 0.002' thou' now..



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