I'm suffering from a poor running 1975 cj5 258 I-6. Looks I need an ignition upgrade but I'm not sure about which one to use. I must have the prestolite system? On another thread jeephammer spells out how to do it but I can't always tell what info is for the V8 or I6. I think I need the Stealth HEI system but I need more specific info on the distributor type and the wiring diagram specific for the 6 cyl 258. Thanks.
If a PO (Previous Owner) hasn't swapped the ignition out already, and you have a plastic vacuum advance on the distributor then its factory Prestolite and there are no practical upgrades,
And it's been a problematic ignition in historic terms.
With an AMC I-6 engine, an actual GM/Delco Remy HEI distributor will usually work with the most reliability.
You WILL need to change distributor gears,
And you WILL need to put the cap, coil, plug wires ect together.
This has the added benifit of using the '76 Blazer with 250 I-6 engine distributor, cap, rotor, and EXTERNAL IGNITION COIL, will give you much better spark energy than the coil in cap version of the HEI.
Again, you will have to change the distributor gear.
The other conversion is to use a factory reman distributor that is dead safe and ready to install.
Since the Prestolite ignition module won't work with the '78-'86 Jeep Motorcraft distributor, you will need to swap modules.
The HEI module is the cheapest and easiest conversion.
Just like any other module,
Two trigger wires,
One 'Green' wire to coil negative,
One 'Red' wire to module power/coil positive,
One 'Black' wire for module 'Ground Path'.
Same as any electronic ignition.
Now, what the HEI Clone fans aren't telling you,
All these clones and there component parts are made mostly in china.
The base materials, machining & components are all questionable.
You MUST do some critical clearance checks before you install a clone.
The truth is, if you use either FACTORY distributors there isn't a dimes worth of difference besides the gears.
The centrifugal advance works the same way, fly weights and springs,
The vacuum advance works the same way,
The basic rules stay the same,
Good spark energy transmission is critical.
You work hard and spend money on a higher spark energy ignition just to screw your self on a few bucks for good cap, rotor, plug wire set.
When your cap, rotor and plug wire set can waste 80% of your spark energy there isn't any good reason NOT to buy quality parts for the spark energy.
You can buy cheap wires for cheap,
You can buy cheap wires that are flashy for big money,
Or you can spend about $80 on wires that will last 10 years and work really good.