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post #1 of (permalink) Old 09-27-2000, 04:35 AM
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TFI coil is getting hot.

I did the TR upgrade. Now the TFI coil is getting very hot. I rewired the engine compartment while doing the upgrade. How hot does this coil usually get?
Thanks for any help.

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post #2 of (permalink) Old 09-27-2000, 09:02 AM
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Re: TFI coil is getting hot.

When you rewired the engine compartment, what's that mean? Ripping out the old harness and chucking it, and wiring from scratch? replacing old wires in the old harness...? etc.?

Since you have a '79 CJ, your positive coil wire coming from the module has a resistance built into it. If you replaced that wire with just a straight wire, that'd be your problem. I had to wire my '77 from scratch, and didn't know to put in the resistor, and the coil got extremly hot, and the jeep would run intermittently.

The well's part number is AL795 for a ceramic resistor, I'm not sure what part number the resistor wire is, but you can use one _OR_ the other, do not use both in conjunction, as this will starve your coil for voltage.

If you did put the resistor in there, and the coil is getting hot to the touch, I've been told this is normal, and my coil does seem alittle hotter than the surrounding engine, but so long as it works, I don't worry too much.

hope this helps.

Florida Mud CJ-5
'77 RB304, t-150 D20 4" 35" swampers
post #3 of (permalink) Old 09-27-2000, 09:12 AM
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Re: TFI coil is getting hot.

Does the module have any resistance before it as well? Mine just has straight wires coming from whatever I could find under the dash.... Could be why its melting down [img]/wwwthreads_images/icons/crazy.gif[/img]

Restoring a '74 DJ-5C [img]/wwwthreads_images/icons/cool.gif[/img] Its missing the alternator. At first the Ammeter gauge just didn't work but now its missing an alternator [img]/wwwthreads_images/icons/crazy.gif[/img]
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post #4 of (permalink) Old 09-27-2000, 12:49 PM
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Re: TFI coil is getting hot.

Both power wires to the module get a full 12 volts full time.
Red is the 'Kicker' from the starter solenoid that powers the module during cranking.
White is the 'Run' wire that powers the module during operation.
Both can be wired together so both get power anytime the key is in the 'RUN' position or the 'START' position.
In fact, you will be delivering twice the current to the module, and it can extend the life of the module, and give you a more powerful ignition.

Check the resistor in front of the coil.
The Motorcraft/ DuraSpark ignition used a resistor wire that was 47" long, and 1.35 Ohms resistance to feed the ignition coil.
If that wire was removed, or has gone bad, it can cause the overheating of the coil.
Auto Zone P/N (Wells) F-799, Around $10.
There are also a multitude of porcelain 'Pot' type resistors out there, and they will work, but he resistor wire is far more dependable.

You may also have a ground problem for the coil.
The coil grounds through the green wire to the module.
The wire may be degrading, the connectors may be corroded and degraded.
The entire ignition system grounds through the black wire from the module to the distributor.
If those wires or connections are corroded, you may not be grounding the coil.
ALSO, the engine block it's self may not be properly grounded.

Make sure you have at least 1.35 Ohm resistor or resistor wire in front of your coil when the key switch is in the 'Run' position.

Run a separate ground wire from your primary ground (battery or primary grounding lug) to the black wire that comes out of the module, and SPLICE into that wire.
Don't cut the black wire from the module, just strip a spot back, and solder on the new ground wire. Don't forget to wrap the joint up moisture tight.
(The engine block never was a dependable ground)

Run a new ground wire to the engine block, and use 'Star' washers so the rust/ paint/ corrosion/ mud/ crud doesn't cause problems again.

Check all wiring harnesses, and clean all connectors thoroughly.
Fill connectors with 'Dielectric' grease before you reconnect them.

Check for resistance from the module green wire connector to the coil green wire connector. There should be any to speak of.

See attached wiring harness graphic for the general idea of how everything should go together...

"I Have The Body Of A God... Buddha"
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post #5 of (permalink) Old 09-27-2000, 12:55 PM
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Re: TFI coil is getting hot.

I missed checking the box...
Here is the graphic.

"I Have The Body Of A God... Buddha"
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File Type: jpg 9-223662-PermanentIgnitionHarness3.jpg (37.1 KB, 2 views)
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