I didn't know much about the 258 I-6 until recently. I do know a considerable amount about ignitions. I put the information and know how together to create this document.

Ignition Up Grade For The Jeep 258 Cubic Inch Displacement, Inline 6 Cylinder Engine

The Jeep 258 CID I-6 from 1978 to 1990 are eligible for this upgrade.
The 258 I-6 from '78 to '90 used the same Motorcraft distributor for all variations.
(If you have a 258 CID I-6, 1977 or older, I urge you to see below*)

The distributor type is one of the most dependable ever released from the factory.
The distributor it's self is a very good unit, and can easily be tuned and used for even extreme performance upgrades.

Jeep used the small 'well' type distributor cap, short rotor, low energy ignition spark plug wires and low output ignition coil are the problem.
The distributor cap design is left over from the 1920's. (WWI technology)
The plug wires haven't changed in any distinct way since the 40's. (WWII technology)
The ignition coil is still based on the oil filled units that appeared in the 1920's. (WWI)

The below described upgrades use as many stock, off the shelf parts, as possible, so they can be replaced at any parts store. This keeps cost and replacement parts availability problems to a minimum.
I also try not to get away from factory groupings. If I use all parts from the same year, then it makes it easier to remember where things come from.

Stock Parts To Replace: (stock jeep components)
Distributor Cap, Rotor, Plug Wires, Distributor Advance Springs, Ignition Coil.

What To Use For Replacement UPGRADE:
FROM: For A 1981 Ford F-150 Pick Up Truck With A 300 CID I-6 Engine.
Distributor Cap Base,
Distributor Cap,
Rotor,
Spark Plug Wires,
Ignition Coil,

Distributor Centrifugal Advance Springs;
FROM: Aftermarket Supplier.
Mr. Gasket P/N 925D

This upgrade will bring your Jeep ignition system into the mainstream 70's technology.

HIGH PERFORMANCE UPGRADES:
Once the cap, rotor and plug wires have been upgraded, then you can use some 80's technology in the form of the THICK FILM INTEGRATED (TFI) ignition coil.
The TFI coil is Motorcraft's answer to the GM HEI coil, and out preforms the common GM HEI coil by about 1-1/2 times.
(yes, that's correct, the TFI coil stomps the GM HEI coil)
The TFI coil will work with ALL of the DuraSpark modules. It's an odd looking thing, but can be mounted in any orientation (even up side down).
The coil from a '84 Ford F-150 Pickup with a V-8 engine (WITH-EEC). The coil runs about $20 in discount stores. GP Sorensen P/N GC407S. AC Delco P/N F503Z.
Borg-Warner P/N E-92,
Standard Ignition P/N FD479,
Niehoff P/N FF-179

The next HUGE jump in ignition performance is the CAPACITIVE Discharge Ignition (CDI).

All factory ignitions, and most aftermarket ignitions supposed to be upgrades for the Jeep are still INDUCTIVE discharge ignitions (IDI), including the extremely expensive D.U.I. ignitions and all JACOBS ignitions.


Multiple Spark Discharge (A CDI module upgrade) gives vastly superior ignition energy on all counts. Spark Duration, Spark Voltage, and Spark Amperage. In all areas the MSD Capacitive discharge module driven ignition will out preform the Inductive ignitions in all areas, from 100 to 1,000%.
MSD is the biggest and best bang for your bucks.

The MSD 6 series units are compatible with all Motorcraft distributors and ignition coils.
The MSD 6A unit is enough for most stock or lightly modified applications. Around $135.
The MSD 6AL unit is the Cadillac of the 6 series with compatibility with all of the usual MSD timing devices, and it has a built in Soft Touch Rev Control. Around $175.
The MSD 6 Off Road, This unit is built like a tank. Epoxy sealed for water resistance and equipped with Weather Pack water proof connectors. Around $215.

Use Wiring Adaptor P/N 8869 to connect the Motorcraft distributor connector to the MSD harness. (Around $10.) This wiring pigtail keeps you from having to cut into the distributor wiring or the MSD wiring, and it keeps the distributor pick up coil polarity correct.

*1977 And Older 258 CID I-6 With The Delco Breaker Points Style Distributor.
You have three choices,
1. Up Grade to the Motorcraft distributor & DuraSpark ignition module, and add the upgrades described above for the Motorcraft distributor.
2. Use an electronic ignition conversion kit for the Delco distributor, and use the DuraSpark or MSD ignition modules, but you will have to go to the aftermarket for adequate distributor caps & rotors.
3. Use a MSD ignition module that will work with breaker points. You will still have to go the aftermarket for adequate distributor caps & rotors.


So many cats, So few recipes....