Another problem! Bad coil?

[jay79cj7]

My CJ7 258 will turn over but not start.

I hadn't driven it in about 2 weeks, ran it about 15-20 min, and then let it sit an hour or so. I had the radio on for about 20 min. Then the problem started. The coil was hot to the touch, which I think is unusual, but I'm not sure. It seemed too long since I had run it for it to still be hot anyway. I put a TFI upgrade in my 79 CJ7 (258) about 2-3 months ago, so I am not very familiar with it. I haven't driven it much since then due to the weather, but it worked well when I did. I swapped the old coil back in and presto, it fired right up. Switched back, and nothing.

1) Did I just get unlucky and picked up a bad coil or what?
2) Is the coil supposed to get warm/hot?
3) Do I have something wired wrong? I don't know where I could have gone wrong; its so simple to hook up. The wires are the same as the old coil. I don't want to buy a new coil just to have this happen again because of something else. I especially don't want to get stranded somewhere.
4) When I get a new one, is there a brand that anybody recommends, or is the cheapy good enough?

Thanks!

 

[derff96963]

I got one possibilty. Have you or anyone else rewired your jeep. The coil is supposed to have resistance wire running from the ignition switch to the coil to drop the voltage to only 9 volts on the positive terminal of the coil. Do you have a simple multimeter that you can check the voltage? If you running it with the full 12 volts you need to put a resistor in between the green signal wire from the negetive on the coil to the ignition module. I fried two ignition Modules before I figured this out. I ended up using 4 8 ohm resistors with 20 watts disapation each wired in paralell to get the right resistance and disapation. This keeps everything cool and running good. Let me know what you find out.

 

[odjeep]

You say you had the radio on, did you have the switch on run or acessory? If you had it on run that could cause the coil to overheat.

od

 

[jay79cj7]

Ooops. I think derff96963 is dead on. Somebody did a hack job on the wiring and I went through and cleaned it up recently. I replaced wires with insulation going bad, etc. Those were some of them... Man, I feel stupid now. Glad I asked instead of just buying another coil.

I think the ignition module must not be fried because it ran fine with the old coil.

So if I put the key in the run position, I should have 9V on the red wire? Is that 9V between the +/- terminals of the coil, or between + and a ground, or what? Why put the resistors on the green (negative) wire instead of on the red? Where did you pick up these resistors? Radio Shack? Is this equivalent to a ballast resistor, and is there one of these I can pick up somewhere that will work? Or can I buy some of this resistance wire somewhere?

Sorry for all the questions. I just fixed my transmission to transfer case adapter, and the 4wd shift mechanism yesterday and was all proud of myself and then this happened 20 min later. What a downer.

 

[derff96963]

It is supposed to have 9 volts between the positive on the coil and ground. One thing you could always do it just leave it how you have it. If you have 12 volts on the stock coil you will be getting a good bit more power than you are supposed to have just like that. You can leave the spark plug gap at .045. However the TFI coil is much higher voltage and will not work with 12 volts on it with out some limiting resistors, As for the reistance wire if you go to autozone thier Wells Part number is F799. If you go somewhere else they should be able to cross reference it for you. As for the resistors on the green wire. The coil gets power running through it from both. If you got 12 volts on the coil and there is no limiting resistors on the green wire it will pull way too much current and can fry both the coil and the moldule. If you want to go the resistor route. I got 4 8 ohm resistors with 20 watts disapation each from radio shack. They you need to wire them in paralell and mount then somehow with some space between. A half inch or so should be fine. Other than that I would recomend getting a spare ignition module and keep it with you just to be on the safe side. It sucks to be stuck somewhere for only a $15 part. Well I hope this help again. One more thing Odjeep is right too don't leave the ignition switch on for any longer than you have too. It is bad for the module and the coil.

 

[jay79cj7]

Thanks guys! I really appreciate your lengthy responses. I already picked up the resistors from RS and will put them in tonight or next weekend.
Again, thanks alot!

 

[jay79cj7]

What grade gas do you use?

Well, after a couple frustrating hours tonight, I got the old jeep running again. Derf96963's resistor method worked great to get the proper voltage drop across my new coil. My new starter solenoid seems to be defective though, which caused me problems. The dang thing works sometimes and sometimes not for no apparent rhyme or reason. I hear it click, so I know it is engaged, but the starter doesn't turn. Then I can take a jumper and go across the two solenoid terminals and the starter goes. Then all of the sudden it started responding to the key again later in the night. I am clueless as to why it is inconsistent. I guess after replacing my new coil now I can replace my new solenoid. And at Odjeep's advice, I will make sure I don't have the key in the run position anymore to listen to the radio.
Now I can brag about what I fixed... The transmission to transfer case adapter was broken, so there was NOTHING securing it in place. :shock: On top of that, the rubber transmission mount was rotted away, and the torque arm bushings weren't even there! And I wondered why I got such a loud noise every time I hit a bump! Funny thing is it really wasn't as bad as I would think it should be. So I removed the transfer case, both driveshafts, replaced the u joints while I was at it, and put it all back together again. And I replaced the vacuum shifter so I have 4wd again. I was quite stoked when I drove the thing out of the garage and the ride was smooth over bumps and I didn't get the annoying "wheel hopping" when I accelerated from a stop. I love that feeling of fixing something all by yourself. And then the thing wouldn't start... Typical.
Thanks everybody!