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Author Topic: 73 Imperial Ignition Meltdown!  (Read 506 times)

Stitcherbob

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73 Imperial Ignition Meltdown!
« on: August 14, 2008, 09:13:38 PM »


This is why my 1973 Imperial would occasionally not start.....melted epoxy in the ignition computer tells me it got a little hot under the collar.....







So I heated it up with a heat gun set on 1000 degrees F to show you what makes that little black box tick....



Not much there....maybe Steve or Bill can back-engineer this thing and build us some hotter set-ups

BTW, I swapped on one that Steve gave me and it started right up....

stitcherbob2008-08-15 02:22:20
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Dan Cluley

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73 Imperial Ignition Meltdown!
« Reply #1 on: August 15, 2008, 01:16:57 AM »

So those must be mounted with the short side at the bottom?
 
The one in the Dart leaked out the long side.
 

 
Did yours make a big mess on the sheet metal too?
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Stitcherbob

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73 Imperial Ignition Meltdown!
« Reply #2 on: August 15, 2008, 06:01:58 AM »

Mine was mounted as picture 1 shows.....dripped all over the heater box because these are mounted on a stepped out sheetmetal bracket (to promote cooling it appears...)

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Bill Mounteer

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73 Imperial Ignition Meltdown!
« Reply #3 on: August 15, 2008, 07:20:00 AM »

Interesting that the stuff melts. Usually these kind of devices are potted with an epoxy mixed with fine sand. The sand makes the epoxy into a better heat conductor and helps to keep the device cool. As far as reverse engineering, I'd bet there are already lots of re-designed boxes out there, however in most cases the best one will still be the original Mopar design. Guys that design automotive electronics really do a great job, their stuff not only works well, it handles all the abuse people throw at them.

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Jimmy

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73 Imperial Ignition Meltdown!
« Reply #4 on: August 15, 2008, 09:22:06 AM »

No need to engineer a better one, just throw a $30 spare in the glove box and install it when you need it.
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Matt Aker

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73 Imperial Ignition Meltdown!
« Reply #5 on: August 15, 2008, 11:49:56 AM »

I don't know what they use on the aftermarket boxes.  It's a black epoxy-like gelatinous goo that you can leave an incriminating fingerprint in.  One wouldn't think that it would take very much heat whatsoever...
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Stitcherbob

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73 Imperial Ignition Meltdown!
« Reply #6 on: August 15, 2008, 05:49:06 PM »

If you use a heat gun and a fine point blow gun, you can liquify and blow the offending mess off of the firewall or heaterbox and then just clean up the residue with mineral spirits.

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Ken

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73 Imperial Ignition Meltdown!
« Reply #7 on: August 15, 2008, 08:14:33 PM »

Bob, I seem to remember hear, via one of my instructors at De Anza Auto Tech, lo over 16 years ago, that the problem with the epoxy melting from the ignition box was an  early problem, and it was rectified quickly after 1973 (the man used to be the head of the department, and also was the instructor for the Plymouth/Chrysler ...later Ford/AAA Troubleshooting Contest).

Obviously it looks like yours is the OE item

BTW, Chaz has a new alternator and electronic ignition system now, and I just had a recommended shop do some tweaking to the carb and ignition system, other than finding the #5 cylinder has lower compression than the rest (75 vs. 100) he runs like a champ.

Now I need to throw the headlamp relays and maybe even one for the blower fan on 'im.


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Stitcherbob

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73 Imperial Ignition Meltdown!
« Reply #8 on: August 16, 2008, 07:11:04 AM »

Great.....the replacement box is from a '72 !

The service manual said not to touch the transistor on the front while the engine was running because of shock hazard. I would also surmise it gets hot, too


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Bill Mounteer

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73 Imperial Ignition Meltdown!
« Reply #9 on: August 16, 2008, 09:59:51 AM »



Yup the transistor will get hot!. The aluminum U-shaped frame around it is a heat sink as are the little aluminum tabs on the inside of the box.  The strips inside the box will conduct heat away from the internal transistors to the steel outer case. The case loses the heat partly through conduction to the firewall via the mounting bracket, but mostly by air flow across the big heat sink on the front. So make sure the mounting bracket to firewall and the regulator to bracket have good mechanical, electrical and heat conduction connections to the firewall. Then make sure the front heat sink is clean and not covered with paint/under coat/ greasy grime etc and that the air flow isn't blocked by wiring or plumbing. If you want to greatly improve the heat conductivity of your various bolted connections, coat the mating surfaces with heat sink grease.

Note there are two types, conductive and non-conductive. For this application you want the conductive one. If you can only find non-conductive, run a short wire jumper from one regulator mounting screw to one of the bracket to firewall bolts. This will give you a good electrical ground.
Fury4402008-08-16 15:19:03
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