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Discussion Starter · #1 ·
I was having a problem with my jeep mis-firing, building up and then backfiring. Took it to the dealer after I replaced everything except the coil (thought it was ok about a year old). Dealer told me it was the coil. They took the coil off tested my jeep and it ran fine. Then they put the old coil back on and it still ran fine. I notice now that sometimes it starts hard and other times it starts up fine. I am looking to upgrade the coil. Any thoughts out there? What kind of work am I looking at to make an upgrade to an MSD coil or some other kind of coil? Would it be worth my time and money?
 

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First off, you want to make sure it's actually the ignition coil making the trouble for you.
It's a fools trail when you start changing parts randomly...

With a '93 4.0L you are fully computer controlled, and making bad choices will affect the computer.

If you haven't had a good old tune up in a while, it's probably a good idea to change the cap & rotor for some brass terminal premium ones.

For you and the '91-'93 4.0L guys, Motorcraft was still making the distributors at this point, so there is an upgrade... (nothing for the '94 to current guys... Yet......)
For the larger cap and taller rotor,
Advanced Auto, Cap Adaptor, p/n FR 138
Advanced Auto, Distributor Cap, p/n FR 123M
Advanced Auto, Rotor, p/n FR 134

This will move you up to a large diameter cap and that will help prevent cross fires and ground fires.
 

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See, this is how posts get diluted to where the original poster can't get his problem solved...

Please use search next time...
If search doesn't turn up anything (like about 4,000 posts on this very subject), I'll be glad to answer your questions for the 4,001 time....
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'79 is a 258 CID (4.2L), not a 4.0L, and is an entirely different distributor and ignition system.

If you want the low down on the '79 258 I-6, it's a,
Cap Adaptor, Distributor Cap, and Rotor from a '82 Ford F-150 Pick up with 300 CID I-6 engine.
Plug wires from a Jeep '91-'93 with I-6 4.0L

Try http://www.shortwheelbase.com tech section (a very good site!), or

http://www.jeepz.com/modules.php?op=modload&name=Howto&file=engine_tfi
 
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