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TR upgrade question...

517 views 16 replies 5 participants last post by  **DONOTDELETE** 
#1 ·
OK, What's the real scoop? Do I or do I not need the resistor on the firewall that I used with my old ignition? The instructions said to use it, but I read recently to eliminate it. Which way works better?
Thanks.



'86 CJ-7, 360, TFI, 727, OEM Dana 44 rear w/Truetrac, Dana 30 w/Powertrax No-Slip, 4" Superlift, 4:11s, Warn HS9500i
 
#2 ·
mmm.. the instructions i have.. say.. NO resistor.. that the tfi coil takes all 12 volts..

any ford guru's here.. i am about to put it on mine this weekend.. if the junkyards around here ever open up.. jeesh.. youd think it was a holiday or somethin...

http://www.jeepgod.net

84 CJ-7 401/T-18/D20/D44/D60w/4.10&Detriots/YJ frame & tub/35x16x15 Boggers
survival is instinct, but living takes guts
 
#3 ·
Bill, and Jeepgod... your questions and answers are good...however there seem to be mixed results in coil longevity using the full 12 volts to the coil. A TFI coil is engineered to be used with the FOMOCO TFI ignition system. The OEM Jeep FOMOCO system uses a different ignition module and distributor. This raises questions about pulse time, width and TFI coil saturation using the OEM Jeep FOMOCO ignition module. I believe this is where the variance occurs. If the module produces a wider, longer lasting pulse the coil become saturated for a longer time. There is little time for the coil to cool before the next pulse. This leads to premature failure. Another ignition module (AutoZone, Pepboys, etc.) may produce a shorter pulse and the timing works out OK. This does not burn up the coil. Like my kids are fond of saying: "It's the same thing, only different." I don't have the insturmentation or the desire to do follow up on this question so I'll just stick to my GM HEI ignition.

 
#5 ·
ok.. so you are running.. 4.6 volts.. mmmm.. Elusive is running the full 12 volts in his.. and they are not lasting.. but a month maybe..
and i understand what you are getting at leve.. mmmmm... ill will some drinkin tonight.. and some thinkin.. and maybe some research this weekend... if im not that hungover.. /wwwthreads_images/icons/laugh.gif..
ill see what i can dig up.. and expeirment with..

http://www.jeepgod.net

84 CJ-7 401/T-18/D20/D44/D60w/4.10&Detriots/YJ frame & tub/35x16x15 Boggers
survival is instinct, but living takes guts
 
#6 ·
lindy80cj7, 4.7 DC volts does seem very a low coil voltage. I'd be happier with it being between 8.2 and 8.9 DC volts. If you're using a resistor, try replacing it with one of a smaller ohm value. The smaller the ohm value will result in a larger voltage to the coil.

If the resistor is in the form of resistor wire then cut out about 1/3 of it's length. That should bring up the voltage to about the correct voltage.

It is true that with the higher voltage to the coil, a higher spark output will result from the coil.

Jeepgod, let me know what you come up with. If Elusive's using the full 12 volts and the coil is not surviving, then the problem is clear.... full voltage is killing the coil. Resistance should be placed in series with the coil to cut down the voltage to the coil.

 
G
#7 ·
jeepgod,
Your instructions may say no resistor because the stock positive coil wire is already a resistor wire. If it has been replaced, then yes a ballast resistor is necessary. Elusive will have better luck with coils if he would step it down to about 8.5 to 8.9 volts.

'75 CJ5,258 w/Howell EFI,T18a,4.27's,33's,On-board air,Warn 8274
 
#9 ·
I took the ballast resistor out of the circut, and didn't notice any difference in starting or acceleration. I just re-installed it back into the system to help the coil last longer.
BTW, I'm getting about 5.2 volts at the coil at key-on and around 10.5 volts while running. Does this sound about right?


'86 CJ-7, 360, TFI, 727, OEM Dana 44 rear w/Truetrac, Dana 30 w/Powertrax No-Slip, 4" Superlift, 4:11s, Warn HS9500i
 
#10 ·
Bill, it seems something is not quite right.

Ususally in the START mode full 12 volts are applied to the coil. This gives the hotter spark and aids in starting a cold vehicle.

When in RUN mode the voltage is lowered to between 8 and 9 volts to pereserve the coil.

 
#11 ·
LEVE- Now you lost me! How would a ballast resistor adjust the voltage to the coil? I could understand it being hotter while running, due to the alternator's input to the system. These readings were taken AFTER the ballast resistor was hooked back up, and the readings are at the coil's terminal. I'll try to get some readings on the other side or the resistor tomorrow.
Are you saying I may have a crossed wire from the module?
I'm confused...:)

'86 CJ-7, 360, TR ignition, 727, OEM Dana 44 rear w/Truetrac, Dana 30 w/Powertrax No-Slip, 4" Superlift, 4:11s, Warn HS9500i
 
#12 ·
The ballast resistor is switched in and out by the ignition switch. When the ignition is in START mode no resistor is present. When the ingnition is in RUN mode the resistor is switched into place, in series with the coil.

When a two resitive devices are placed in series they form a voltage divider circuit. The voltage divides between the two devices according to the resistance of each device.

If your system were working normally, the higher voltage would be measured when the ingnition key were turned to START. When the key were moved back to the RUN position, there would be a lower voltage applied to the coil.

It does seem you've got:

1. Some mis-wiring.
2. TWO balast resistors in series with each other. Is is possible you have the resistor wire still in place and an external ballast resistor wired in as well?

Click on the figure bleow for a better description of the ballast circuit...


 
#13 ·
Thanks for the info. I went back and looked at the installation diagram, and I see now where the module switches the voltage during starting. Now I understand!
I'll chase some wires and see what's up.
Thanks again.

'86 CJ-7, 360, TR ignition, 727, OEM Dana 44 rear w/Truetrac, Dana 30 w/Powertrax No-Slip, 4" Superlift, 4:11s, Warn HS9500i
 
#14 ·
Sorry for butting in but I've got a question for you Leve. The input voltage to my tfi coil is 12 in strt and run. at one point somebody put in a starter relay for a 4 cylander but I am going to fix that soon. But the voltage at the coil is about 2 to 3. MY question is how to I get that up to at least 8 or 9 volts. I dont think its the resister wire because I am getting 12 into the coil but it is dropping it to 2, this is a new coil and modual. thanks

88 YJ:4.2 I6 TR upgrade and MC2100
 
#15 ·
If the input voltage is full voltage (12) at the coil, in both start and run modes, then there is NO resistance in series with the coil. The coil then expends full power.

When you describe 2 to 3 volts at the coil, where are you taking the reading? It should be the Plus side of the coil, but it sounds like you are measuring the voltage drop across the coil. This would be incorrect.

The minus side of the coil is the pulse return line to the ingintion module, and is not where you'd want to measure the 9 volts. That would mean the coil would only drop 3 volts... and that's not a lot of power being expended in the coil!

Also when taking the voltage reading at the Plus side of the coil, unhook the starter cable. Often when you put such a huge load on the circuits, crazy readings can occur depending upon what type of meter you're using. The voltage can be drawn down and you get an inaccurate reading.

So, by putting reistance between the 12 volt source (run mode) and the coil the two devices will form a voltage divider circuit. The voltage then drops in accordance with Ohm's law between the three devices (1. Resistor; 2. Coil; 3. Ignition Module). The resistor now being in the circuit drops some of the voltage... and depending upon how high a resistanc value, the amount is about 3.5 volts, which then means that about 8.5 volts is now avaliable at the Plus side of the coil.

Is this any clearer?

 
G
#17 ·
when you test the voltage at the coil the engine needs to be runing. Other wise there is no current flow through the resister and the voltage will not drop acrossed it. therefore you will read 12v at the coil even if the resistor is installed.

bandhmo

 
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