TFI voltage results not good.

[irbob]

I finally got around to checking my TFI coil volts and here is what I found:

Key on engine off
5.4v at coil

Engine running
-2.2v across coil
8.4v batt. to coil pos.
10.5v batt. to coil neg.
14.7v across batt.

The brown resistor wire isn't connected to the coil. It is tied off and wrapped around another wire to keep it in place. It reads the same volts as the pos. coil wire.

Anybody know why I'm not getting the 12 volts to the coil? TIA

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[Bnjnz]

i just did the TFI myself and would like to check the voltage to compare. i bought a multimeter to check it but have never used one before. could you maybe give me some instructions on how to test the voltage? thanks

benjamin
1991 GW

[irbob]

Set the meter for DC. Check the volts across your battery to see if it's working. Should be 12-14 volts. Hold the negative lead on the neg batt terminal then touch the positive lead to each side of your coil and record the results. Also check across the pos and neg of the coil and check the pos side of the coil with just the key turned on with engine off. Let us know what you found.

[Bnjnz]

thanks for the info. i got exams this week so all wag work is postponed. but when i am done i will check it out. hopefully we can figure out the low voltage problems

benjamin
1991 GW

[wagdriver]

Bob I just went out and check my 88 GW coil voltages. They are as follows,
Bat- coil + ign on ~7,3Vdc
Bat- coil - ign on ~2.6Vdc

Bat- coil + eng run ~11.6Vdc
Bat- coil - end run ~8.3Vdc

My system uses the Ford ignition module so it may be different from yours. If you measure the voltage at the + terminal of the coil and end of the resister wire, that is not connected,

coil plus wire----------[+-----end of resistor wire

You are essentially measureing the same point hence the same voltage.


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wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[This message has been edited by wagdriver (edited May 06, 2001).]

[This message has been edited by wagdriver (edited May 06, 2001).]

[This message has been edited by wagdriver (edited May 06, 2001).]

[wagdriver]

Bob I have been kicking around your voltage readings and have come to a conclusion you might want to check out. From all of the wire diagrams I have been able to find, I may have found some of your problem. Did you use the original wire from the old coil to hook up your TFI coil? If you did I suspect that you still have the resistance wire in the circuit, which would account for not getting a full 12V at the coil + terminal. It would appear to me that you need to some how get a full 12V from the run wire on the ignition switch. Do you have access to a Haines manual #50029? It gives most of the ignition start wire diagrams for most of our Jeeps. I think the way the circuit works is that, when the start solenoid is activated, it by-passes the run wire temporaly and applies the full 12V to the coil to start, when switch returns to the run position, the resistor wire is in the circuit limiting the voltage to the coil. Check it out and see what you think http://www.ifsja.org/ubb/wink.gif I'll do some more checking, I am insterested in doin this mod myself!

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wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[This message has been edited by wagdriver (edited May 06, 2001).]

[irbob]

Some good words wagdriver, I will get to checking it out a little better prob next week. A lot going on around here right now. Thanks.

My system uses the Ford ignition module so it may be different from yours. If you measure the
voltage at the + terminal of the coil and end of the resister wire, that is not connected,

coil plus wire----------[+-----end of resistor wire

You are essentially measureing the same point hence the same voltage.

I'm kind of confused about this. Couild you maybe refrase it so I can better understand what your trying to tell my little brain. http://www.ifsja.org/ubb/biggrin.gif

------------------
My FSJeep Site (http://fsjeep.homestead.com) <----Click one of these----> IFSJA Sticker (http://fsjeep.homestead.com/stickerpage.html)
http://FSJeep.homestead.com/files/Sig_Pix/sig_pic.jpg
"Mystery Machine",360,K&N,TFI,Custom Turbo II 2.5" Exaust,999 Auto,NP229,F/Dana 44F,R/AMC 8 7/8",32X11.5 Cooper Wildcat MT's,RS 9000's,AALx4,2" blocks,3" Body Lift.

[wagdriver]

If you measure the voltage any where along the dotted line up to [+ you will get 12V if you continue down the dotted line to the right you will still get 12V because it is the same point http://www.ifsja.org/ubb/biggrin.gif

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wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[Michael F]

I have been using a Jacobs replacment coil for the duraspark system and was told by Jacobs the coil was a 12v coil, so I ran 12v to it and the ignition module has always ran to hot to touch and replaced it with a different one, same thing. I then put the resistor back in to drop the voltage and the ignition module cooled down.

I looked at the diagrams for the TFI fords and found the TFI coil has a resistance wire to them that would suggest that they also do not use full 12v. I also started to have intermittent ignition failure that would suggest the duraspark module can not handle 12v being fed to the coil.

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81 Cherokee Laredo WT
56,000 orig. miles (not the engine I6 to V8 conv.)
360/727/208/3.31w/tracklock/35x12.5 ProCompMT/double diaphragm brake booster
4" BDS lift/TrailMaster SSV shocks
79 Cherokee Chief WT (snow plow)
360/400/QTw/LR/3.54/31x10.5

[wagdriver]

Irbob, maybe you are chasing something we don't need to be chasing, from what MichaelF is saying, granted the text of article stated that the coil is capapable of handling the 12V, and more power in equals more power out. We'll just have to do some more research I guess. I got to the article from your web site, and it said there was a schematic with it, however I could not find it, am I missing something here? http://www.ifsja.org/ubb/smile.gif

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wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[irbob]

The schematic no longer exists I guess. I didn't see it eather. I would like to see how it acts with 12 volts going to it though.

[Veepster]

I am quite familiar with the lack of a resistor wire..as last year I went through 3 coils, and 2 ignition boxes...what I had always thought was that the coil could not handle the full 12 volts....maybe the ignition box can't handle it either??........

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Peace.............BartG

the Green Flash!
360ci
Custom 4v TBI
Edelbrock Performer Manifold
TH400, QT with low
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Thorley headers, 3" exhaust, Dyno Max
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Custom billet shift knob by Millerluck
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[nograin]

Dr. Jacobs suggests in his book that the resistor should be used for most situations, but a clever way to get a more intense spark is to have switch and relay to bypass the resistor at WOT.

[wagdriver]

I guess that with all the kicking around we have done here, it would seem that running the resistance wire is the way to go, from a reliability stand point. As Nograin and Veepster have suggested you could by-pass the risistor and pay the consequences. How many times are you going to run wide open throttle? I would think that if you are getting a noticeable difference with what you have now(are you?)it may just pay to leave it. My suggestions were based on the assumption that running 12V to the coil was the goal for more spark power and reading the article suggested that that was possible. I don't think you want to get in to a position where you could be left stranded for a marginal power gain, and an ignition module falure will leave you sitting beside the road. Been there, done that, and it damm near ruined a good vacation to boot. http://www.ifsja.org/ubb/frown.gif

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wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock

[Veepster]

so the conclusion is......

Leave the resistor wire no matter what ignition you are running..

right??

which means I better put mine back in!!!

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Peace.............BartG

the Green Flash!
360ci
Custom 4v TBI
Edelbrock Performer Manifold
TH400, QT with low
4" skyjacker suspension lift, 3" body lift Rancho 9000's
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
Custom billet shift knob by Millerluck
50%Luxury Car, 50%Tractor
http://www.teamgodspeed.com

[wagdriver]

Veepster'
from what has been revealed here it would seem that would be the case. After all, we want reliable vehicles. That is one of the things that attracts us to these beasts isn't it? With your experience I would say that the resistor wire would be the way to go. You can't argue with success, and I am sure you have much more experience in these matters than I!
Irbob,
It would seem that these guys have a pretty strong case going here, as I said previously I don't think you want to sacrifice reliability for a marginal gain in power. http://www.ifsja.org/ubb/biggrin.gif
I wish we could see the original wireing diagram, I have looked for it, but have not been able to locate it, maybe I just plain missed it, it probably got trashed with he hack job. May be some of the other guys know how to get to it.

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wagdriver
88 Grand Wagoneer
135k and still going
K&N everything else stock
95 Dodge Ram 2500 360 stone stock