TFI conversion "NEED HELP!"

[Bozz]

Got everything (I think) installed and the jeep won't start????? Have 3.4 VDC at the Red w/blue strip of the ignition coil. Looks like the same wire runs to the starter soleniod and then splices into a orange w/green stripe wire running back to the firewall, which I would assume goes to the key. The orange w/grn stripe wire is getting hotter than hell??

SUGGESTIONS?????

Thanks.

[Stuka]

take a spark plug, and plug it into one of your plug wires, have somebody turn the engine over while grounding the thread area of the plug on the intake or something. You should get a consistant blue spark.

if you dont, then we can start tracing back everything. But it sounds like you may have something wired wrong if one wire is getting hot (btw: colors dont help us, amc liked to change colors like... every 6 months lol)

[Bozz]

Stuka,

I pulled the plug off the ignition coil and have 12 VDC with it unplugged as soon as I plug it in the voltage drops to 3 VDC. I checked the wire going to the cap, from the coil, and it also reads 3 VDC. Pulled one of the plugs and there is no spark.
When I replace the stock coil with the new TFI coil there was 3 wires going to the top of the coil. A green and 2 reds. I spliced the 2 reds together and connected them to the red wire off the new TFI coil. The green (ground) went to one of the green wires off the plug of the TFI coil and the other green off the TFI coil went to the stud of the bracket. There was a little module that the wire busted off of and I ran down to the NAPA store and they said it was not needed since it was a noise suppressor for the radio system. Other than that the wiring is as it was???

Thanks.

[Hand's End]

Sounds like the wires are crossed to me. I was working on mine today. It should be similar ('89 G/W). I had 1 wire with a stripe that goes to + on coil. The other 2 wires were spliced and went to - of coil and to resistor for radio noise.

Maybe you got the + and - wires mixed? You said you had a green and 2 reds. Maybe the colors don't match up from harness to new coil.

[Bozz]

Yeh,

Pulled the plug and the red's are positive. If you follow the red back to were it splices and then back it goes to the positive of the soleniod.

I think I have a bad coil. I took a ohm reading across the coil and only have .6 ohms. I believe it should be about 50 ohms according to the guy at NAPA.?????

[Hand's End]

I can check ohms on mine in AM if you like...

[Bozz]

Hand's End,

That would be great unless someone knows what it really should be. The guy at NAPA that I talked to said the book indicated it should be between 48 - 5? ohms. I have a IC24SB. Now that I think about it the guy used the part # IC24 when he checked the book....I wonder if they thought the SB was the same but, it really is not. Not much I can do tonight, will continue tomorrow.
Thanks.

[4x4n In A Cherokee In Colorado]

Go from the positive side of the coil to the output(coil wire to dist) with your ohm meter. What is the reading?

That is primary resistance...Should be 8500 to 11500 ohms for TFI coil.

Also if you have not replaced the wire coming from the spark box to the coil, then you still have a resistor wire....It could be bad, that would explain voltage loss. It may read 12 volts without a load, but when you plug it in, there is current flow, that will lower voltage. It should only lower voltage around 5 volts if working properly.

The reistor wire is around 5 feet. It splices from about the brake booster, and splices where you see the splice going to the starter solinoid.

[4x4n In A Cherokee In Colorado]

I just done the TFI thing last weekend, had a few questions myself...heres a link:

http://www.ifsja.org/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=2;t=024411

[Bozz]

4x4n In A Cherokee In Colorado,

The readings from the positive wire to the coil to the coil output to the cap is 7850 ohms??

[4x4n In A Cherokee In Colorado]

Thats a little low according to Motorcraft specs. But may not be according to NAPA's. I used Motocraft parts so there may be a little difference there. Your still in the ball park and you should still be getting spark with 7900 ohm resistance. I would try looking into the resistor wire. Mine was in very bad shape when I pulled it out and replaced it with a standard wire.

The red is the pos. the green is the ground on the Jeep. Look inside of the coil where it plugs in and you should see a plus and minus. Make sure your green from the jeep is actully going to Minus on coil. And red from the jeep is going to Plus on coil just to double check you are not wired backwards.

The TFI needs at least 8-9 volts to spark.

[Bozz]

ok.

Took the resistor wire out and ran a new 10 ga. wire. Have 11.05 VDC at the + of the input to the coil with the key on, (engine not cranking). Tried to start it and the engine turns over but, no spark. Pulled a plug and no spark??

[Bozz]

Rande,

I did remove the plug from the coil and had 12 VDC. Yes, resistor wire was getting VERY hot.

The jeep ran fine until the TFI upgrade, now it does not run at all. Yes, I realize that you cannot measure coil voltage with a multimeter while turning the motor over. I am an electrician by trade but, not a auto mechanic though.....obviously!!!

[Rande]

Ok, I deleted my post while editing. When you mentioned testing the wire from the coil to the cap, I thought about your poor meter!

Electrician here too, 24 years as a Journeymen.

[4x4n In A Cherokee In Colorado]

Rande if you read a manual on TFI primary coil resistance testing it tell you to go from the Pos. side of coil to the output of coil(coil wire)...
When I just checked my TFI coil the way you said it reads .4 ohm just as BOZZ's is reading .6 this means nothing! If you want to check a coil, any coil, you go from Pos. to coil output. That is the primary resistance per motorcraft manual. By the way my volt/ohm meter still works great.

[Bozz]

Any other thoughts on this guys? I really appreciate the help so far and I have learned something! Hate going to bed with it not working but, hey, tomorrow's another day!

[4x4n In A Cherokee In Colorado]

Rande you dont test the coil while it is plugged in with key on. You can test any coil in vehicle or out of vehicle this way. Bat. Pos. to coil output.

[Rande]

I wonder if you have a bad coil. With the coil mounted, do you get continuity from the + to the mount?

The resister wire is going to get pretty warm but shouldn't be getting really hot. If it is, there may be a short.

Check the connector at the distributor to make sure it didn't get pulled apart during the work.

[Rande]

Ok, I'll shut up now.

[Bozz]

Rande,

Yes, from the + to the mount is .6 ohms. I did double, triple check the connector from the coil output to the distributor cap.

The wire's that I got were from a 1990 ford with a 460. There were two different sets of plug wires available, one for an engine with electronic control and one without. I first got the set for an engine that did not have electronic control but, the wire from the coil to the distributor was the wrong one. I then returned to NAPA and tried the other set and it had the correct wire. Just trying to throw stuff out here.....

[Rande]

The connector at the distributor I am talking about is the wiring from the distributor to the harness and back to the ignition box, not the coil wire to the cap.

[Rande]

Should you be getting continuity from the + terminal to the mount? Its the ignition box that provides the path to ground for the primary side of the coil.

[ January 17, 2004, 10:07 PM: Message edited by: Rande ]

[Bozz]

I am not really sure. If you read thru any coil it will normally have very little resistance, as you probably know. So without any other info, I would say, yes, you should be getting continuity from the + of the coil input to the mount since the mount is ground.

BUT! That does up a VERY GOOD POINT!!!! I lifted the second green wire that I had landed to the mount and.....drumroll please..........WE HAVE IGNITION!!!!

Thanks a million! Hey, what about the resistor wire that I removed??? Do I need to re-install it or am I good with just a regular wire? Sounds like there are two different theories on this???

Thanks,
Dan

[Rande]

The rsister wire should be reconnected. The ignition module won't last very long with 12 volts going to it.

The TFI coil can handle the 12 volts but the ignition module can't. Some on the site have had theirs last a good long time but most have had them burn out in short order.

[Rande]

My understanding of the ignition system on these Jeeps is that the ignition module provides the path to ground for the coil when the distributor tells it to. Instead of the module providing the voltage, it provides the ground. By grounding that second geen wire, you bypassed the module. That second green wire apparently went to a radio supression capacitor.

The + terminal of the coil should not read through to ground when the engine is not turning over.

[Bozz]

Rande,

Appreciate the input and thanks. Reconnected the resistor wire and test started again. Does start much faster than with the old ignition.

Stuka and 4x4n In A Cherokee In Colorado, thanks ALOT for the input and help!

I am going to bed a happy man!

[4x4n In A Cherokee In Colorado]

This is info from a Chiltons shop manual, the 3 inch thick one for your jeep.
Testing ignition system:
Disconnect the coil to dist. leads at the connecter and connect a test light between the + and - coil terminals.
Turn the Ign. switch on. If the test light doesnt come on check the sparkbox ground lead. If the ground lead is in good condition, replace the sparkbox.
If the test light does stay on leave the test light in place and short the terminals on the coil to dist. connector together with a jumper lead,(connector seperated) at the coil side of the connector. If the light stays on replace the sparkbox.

The mag. senser resistance can be tested by connecting an ohm meter to its leads. Resistance should be 1.8 ohms +/- 10% at 77 deg. F. Replace the sensor if it doesnt meets these specs.

Maybe this will help.. Possibly your sparkbox is bad or the Mag. p/u is bad.

According to the manual primary resistance is tested + to - as Rande said. Should be .3 to 1.0 ohms. Secondary resistance should be 8000 to 11500 and tested as I said from Pos. to coil tower. So your coil is out of spec. slightly but I dont think that little would create a no spark situation.....Maybe Rande would know that one.

Any more questions. I have the manual for your jeep handy. Let me know.

[4x4n In A Cherokee In Colorado]

Rande would having a coil that has more or less secondary resistance have anything to do with the module lasting longer or shorter?

[Rande]

I doubt it. The module is providing the path to ground for the low voltage to the coil. I would think that secondary resistance would not have any effect on that. My experience is with transformers. In transformers the primary and secondary windings are usually completely seperate from each other. These coils may be done differently.

I have never checked myself, but I would think the primary winding would connected to the power source and the then over to the module. The + and - terminals being completely seperate from the secondary winding. The secondary winding would then be connected to the distributor cap and the engine block, probably through the mount.

If your manual says to check the coil by testing between the + terminal and the high voltage output, then the secondary windings - connection and the primary windings - connection must be connected together. You are then testing the entire length of wire inside the coil, primary and secondary windings. I should probably test this out myself someday.

My take on the module not being able to handle the constant 12 volts of a bypassed resisiter wire is that it uses a transister to ground the - wire coming off the coil. A transister can only handle so much power. The heat will cause it to fail. How much heat it has to handle is related to the voltage it has to pass, the internal resistance of the transister and the amperage it has to pass. Increase any one of those, and you increase the heat. An electronic signal from the distributor energizes a circuit in the module to enable the transister to conduct.

So, if the coil requires more amperage, then the module has to pass that higher amperage to ground (the chassis). If you feed it with higher voltage, the module is having to pass that on. Either one of which is going to increase the heat produced during the time the transister conducts.

I would like to see a schematic of the ciruitry inside one of these modules. I am just guessing that the module works in that manner. Transisters are used a switches quite often. They can be switched very rapidly and with no arcing like a regular switch would have. They can be controlled by a simple electronic circuit. It makes sense to me that it would done in this way.

Somewhere there has to be a schematic diagram of an automotive coil that I can get a look at. That would show if the primary and secondary windings are seperate or not.

[Bozz]

One other question guys....I drove the Jeep this morning and man what a difference, really impressed. But, the idle would not kick down when I came to a stop??? Related? Do I have to make another adjustment somewhere?

[Bob Barry]

You may have knocked your electric choke connection loose, in which case it would never heat up and never open. Check that the wire is firmly attached to the round cap on the passenger-side of the carburetor.

[Bozz]

Yep, good call. Thanks. Pulling the resistor wire out and then back in I must have pulled it off the connection. Thanks.

[andy d]

coils work by induction. there is no direct path (0 ohms) between the primary and secondary windings of the coil. if there is , then the coil is ng