TFI coil too much for ignition module

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Topic author
mattv
Posts: 35
Joined: Mon Nov 09, 2015 5:01 pm

TFI coil too much for ignition module

Post by mattv »

I've been bringing back to life a 1980 J-20, AMC 360, two barrel, automatic (my dream truck)
It already had front disc brakes and power steering and duraspark ignition
anyway, I upgraded the alternator to 85 amps (to help power an electric fan)
got rid of the amp meter (it had been hot enough to melt the cluster)
and swapped in a TFI coil (with bigger cap and better wires)
I don't remember any "resister wire"
I've got two wires going to the coil (aside from the dist. wire)
it's been running great
I had to replace the timing cover gasket, water pump, starter, solonoid, and now it's eating ignition modules
Does it need a resister wire (after 3 years) ?
should I replace it with a "capacitive discharge" module (Mo' Money)
or will it burn that up, too ?
any help from the jeep lovers would be greatly appreciated
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tgreese
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Location: Medford MA USA

Re: TFI coil too much for ignition module

Post by tgreese »

The resistance wire is a single strand of nichrome wire. Should be there. The resistance wire goes between the firewall bulkhead connector and a splice that goes to the "I" terminal on the starter solenoid. The "I" terminal then goes to the ignition coil as plain wire. Shown clearly on the wiring diagram here https://oljeep.com/gw/elec/80/1980_cher ... yl_pg1.jpg or in your TSM.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

Topic author
mattv
Posts: 35
Joined: Mon Nov 09, 2015 5:01 pm

Re: TFI coil too much for ignition module

Post by mattv »

thanks Tim,
do you suppose if I accidentally attached that to the "s" terminal, I would subsequently "over-amp" the module ?
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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: TFI coil too much for ignition module

Post by tgreese »

NP! The "S" terminal is only live while starting. No danger.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

j10builder
Posts: 92
Joined: Tue Mar 12, 2019 5:28 pm

Re: TFI coil too much for ignition module

Post by j10builder »

I'm going to be doing the something with my ignition. I've already bought the parts (just gotta get the motor back in the truck, it's gonna be awhile). What, exactly does the resistance wire do? Does voltage to the coil need to be tamed? I read somewhere it was just for radio interference but that seems "not right". Mattv, I'm really interested in your opinion on the upgrade. Did it improve performance? I'm also building a 1980 J10 with a 360.
'81' J10 w/all the good same year J20 stuff

Topic author
mattv
Posts: 35
Joined: Mon Nov 09, 2015 5:01 pm

Re: TFI coil too much for ignition module

Post by mattv »

yes, it improved performance.
when I started on this thing it was leaking everywhere and wouldn't idle.
I rebuilt the carb and upgraded the ignition at the same time.
so, I can't give all the credit to the TFI coil
as I recall, part of the "team rush" upgrade was to use a MSD 6 module (I haven't done that)
but, I've read that a capacitive module (eg MSD $$$ )is not prone to letting out smoke (like a part-store-variety module).

does anyone know ? ? ?
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tgreese
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Location: Medford MA USA

Re: TFI coil too much for ignition module

Post by tgreese »

The resistance wire limits current through the coil while running. The resistance wire is bypassed by the "I" terminal on the starter solenoid during starting - presumably for easier starting. The usual concern is not the coil but the electronic control unit (ECU) which replaces the points. There is a big transistor in the ECU that turns on and off to charge/discharge the coil. Too much current will overheat the transistor; usually the potting compound in the ECU melts and signals the demise of the unit.

Yes, you can replace the ECU with the MSD 6 module. You can also use a module from the GM HEI ignition. Any module that accepts a variable reluctance (VR) magnetic signal should work. I'm running a Duraspark distributor with a GM HEI module in my CJ-6. I have the Summit CD module (a MSD 6 copy) for that Jeep, but I have not installed it yet.

Typical problem with this stuff - it usually gets upgraded along with a tuneup. Then it's impossible to say whether the upgrade made it run better or the tuneup, or both.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

j10builder
Posts: 92
Joined: Tue Mar 12, 2019 5:28 pm

Re: TFI coil too much for ignition module

Post by j10builder »

I dove down the worm hole on this subject about two weeks ago when itselliott put the following links up on a different thread on this forum. This isn't directly related to your problem but I figured I'd put it up anyway so some other poor guy can get sucked into it and spend hours reading up like I did.

Good info with pics
http://www.grimmjeeper.com/J-Truck/tfi.html

Here's an interesting thread about hiding a GM HEI trigger in a Duraspark box (post 4 for pic). I seriously considering this instead of MSD box. This guy had all kinds of problems with his conversion, at the end it was a short where the wires entered the box (post 15), might be something to look at on your rig come to think of it, old wires are prone to crack and short from time to time.
https://www.jeepforum.com/forum/f8/stea ... rt-810617/

This goes into all kinds of info and speaks about the MSD box. One note, this mentions in one place to get the cap and rotor for a 89 F0350 with ECC. I WAS NOT able to make that setup work on my distrib. I stuck with non ECC cap and rotor.
http://www.ifsja.org/tech/electrical/ig ... grade.html
'81' J10 w/all the good same year J20 stuff
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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: TFI coil too much for ignition module

Post by tgreese »

Realize there is a big difference between a capacitor discharge ignition module like the MSD or the Summit I listed above and a transistor switch like the Duraspark, HEI or Pertronix. Different operating principle. Both types can be triggered by the Duraspark distributor.

The TFI upgrade depends on the upgraded ignition coil to make a hotter spark. The Ford TFI coil and the GM HEI coil appear to have more turns of wire, as well as a more efficient magnetic design than the cylindrical factory coils that these Jeeps came with. All the other stuff - wires, big cap, big rotor - should be an improvement due to their geometry, but don't contribute anything to spark intensity.

Both the capacitor discharge and the hot EI coils (because the steel is shaped like overlapping Es and Is) make a hotter spark.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

j10builder
Posts: 92
Joined: Tue Mar 12, 2019 5:28 pm

Re: TFI coil too much for ignition module

Post by j10builder »

Thanks Tim. All great info. I've got a feeling the hot rod shop will be selling me an MSD box as soon as I get the engine in.
'81' J10 w/all the good same year J20 stuff

Topic author
mattv
Posts: 35
Joined: Mon Nov 09, 2015 5:01 pm

Re: TFI coil too much for ignition module

Post by mattv »

so, I left my truck outside for five days of snow and twenty below (really) and it fired up.
I've got a NAPA (echlin) module in there, now. are they shy when they"re cold, come on!

as always, I'm thankful to have a sounding board here ( as I don't seem to know any motor-heads anymore).
thanks ya'll

j10builder
Posts: 92
Joined: Tue Mar 12, 2019 5:28 pm

Re: TFI coil too much for ignition module

Post by j10builder »

Great news! Thanks for the info
'81' J10 w/all the good same year J20 stuff
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