I would think...
You would want to wait to see what his 'Additions' were before commenting.
I would also think truthful comment would be a good idea...
If it is the original factory coil changing it will make a difference. The original factory coils had a very low output because jeep were scrimping on parts to save money.
Actually, from '78 to '86, CJ's used a very good FACTORY style ignition coil.
They used the Motorcraft ignition coils, and they were a very well wound (good wires sizes, good winding ratios) that didn't put out excessively high Voltage that sacrificed Amperage or Duration.
The distributor cap is too small a diameter to work with high voltage because of cross arcing. I think the coils were only 18,000 volts.
Wait, first off you said the coils wouldn't produce sufficient voltage,
Now you say the distributor caps can't handle the voltage the coils produce!
Which version do you want to go with!?
Actually, you will find the Jeep/DuraSpark ignition used from '78 to '86 worked pretty well and produced spark energies that were high enough to get the job done.
Usually, from 20,000 volts to 30,000 volts,
They produced those voltages while still producing reasonable Amperage and having reasonable spark Durations.
Anything above about 22,000 Volts, to 25,000 volts is too much for the small distributor cap and short rotor that AMC/Jeep chose to use!
That small cap and short rotor design was dropped by Ford/Motorcraft in '75 when the electronic ignition started being used in most of it's vehicles.
The Ford engineers knew that the small/short cap/rotor couldn't handle the increased spark energy the electronic ignition was going to produce...
AMC/Jeep just didn't take the advice and use the larger/taller cap/rotor when they bought the ignition.
I used the the ignition components from the Ford 4.9 6 cylinder of the same year, they fit straight to the motorcraft base. There is a spacer/adapter which allows you to use the large diameter cap, the Ford standard leads work great and I used the coil also from the Ford which even has the right fittings to match the OEM wiring and fits the existing bracket, it's just a bit longer.
Yes, it's called the 'TeamRush' upgrade,
And it's simply using Electronic Ignition Ford/Motorcraft parts on the AMC/Jeep Motorcraft distributor.
They are drop on-- Direct fit parts from Ford/Motorcraft, and the increase the High Voltage Electrical Current Handling part of the stock AMC/Jeep/Motorcraft ignition.
The Ford/Motorcraft ignition coil will directly replace the AMC/Jeep/Motorcraft ignition coil BECAUSE IT'S EXACTLY THE SAME THING...
AMC/Jeep used Ford/Motorcraft coils, so your 'Change' wasn't a change at all...
I was then able to open the plug gap up to the Ford setting. It works so much better than standard and cost very little to adapt.
The opening of the plug gap IS NOT the 'FORD SETTING'.
When I tell people to open up to 0.045", that is the MAXIMUM you should open up the plug gap...
Most Ford settings are LESS than 0.045".
I know you don't know the electrical or mechanical reasons WHY you can or should open plug gaps up,
But at least you were listening to the instructions and did so...
You have your Mileage Master set up but wil benefit from a better coil, I don't think huge voltages are needed for the 258, just a better OEM coil like the Ford one I used will make a big difference and only cost about $15.
The 'Super Duper' coils have more turns of windings most of the time...
But they are actually LESS EFFICIENT like that.
Most of the 'Super Duper' coils are just quality, factory type coils with odd color paint, chrome, or stickers.
Others have insane turn ratios that drive up VOLTAGE,
but they sacrifice Amperage and spark Duration to do so.
It's much better to use a QUALITY, STOCK TYPE Factory Coil instead of going with one of the 'Super Duper' coils you have no idea of it's performance.
Being able to run a bigger plug gap giving a fatter spark makes all the difference.
Bigger plug gap only increases the VOLTAGE required to ionize the plug gap and does NOTHING for 'Fatter' spark...
Actually, how 'Fat' the spark is has NOTHING to do with the ignition of the cylinder.
The gap will take 'X' amount of VOLTAGE to ionize the gap so the spark can happen.
The larger the gap, the more Voltage it takes to ionize that gap.
The more Voltage it takes to ionize that gap, the longer the ignition coil (step up transformer) has to produce VOLTAGE, and rob AMPERAGE and DURATION to make Voltage.
AMPERAGE IS THE 'HEAT' in the spark.
Amperage is the actual ability to ignite the fuel & air mixture...
DURATION IS THE AMOUNT OF TIME THE SPARK LINGERS OR LASTS IN THE GAP.
The longer the coil is stuck making voltage, the less time the actual spark gets to stay in the Gap to get the job done.
If the Mileage Masters are as bad as Jeep Hammer says and you may want to just lose the whole thing.
Depends on what 'Mileage Master' he has.
If it's one of the 'Do Nothing' modules, there is nothing there to break down.
If it's a Jacobs (which I expect since the OP mentioned the Jacobs 'Super Coil') I've never seen one last this long...
They usually broke down within the first year of use, then Jacobs would stiff arm you when you tried to get warranty.
For a cheap/reliable good functioning set up, switching to the Ford 4.9 components is a great way to go and leaves everthing with an OEM look under the hood.
AMC/Jeep reman Motorcraft distributor for $50,
A cap adapter, distributor cap, rotor & Plug wires from a '82 Ford F-150 with 300 CID I-6 engine will give you some real advantages over the stock version AMC/Jeep used,
And it will clean up the Jacobs stuff if it's failing.