Starting in the 80s the 4.2L came equipped with the Carter BBD (computer stepper motor controlled) carburetor & a pulse air emissions system. This generation of 4.2 Liter engines are notorious for hitting a virtual brick wall when trying to rev past 3000 rpm. This behavior, along with the big tires & heavy duty running gear, left a lot of room for improvement in the test Jeeps highway performance and in it's performance off the line.

Jacobs Electronics sent us one of their "Omni Magnum" Ignition Systems complete with a set of the optional spark plug wires. When it arrived it was neatly packed in two boxes. All of the ignition system wires were already loomed together neatly and plainly labeled.

The Omni Magnum is good to 10,500 rpm, the similar Omni Pak to 6,800 rpm. All Jacobs products are emissions legal in all 50 states and carry CARB E.O. #D-19-19.

The instructions were very clear, simple and brief. All of the parts that we needed to install the system were included - down to the screws to mount it. I was very impressed with the quality of all of the components. Top quality waterproof connectors are used throughout and the ignition system components themselves were completely potted and are highly water resistant.

The "Omni Magnum" system consisted of these main components: The "Omni" unit - a combined variable magnetic "Ultra Coil" and electronic ignition computer unit (the equivalent of their "Energy Pak" computer). The Secondary Trigger - this unit interfaces to the stock coil if it is left in the system and uses it as a trigger signal to fire the Omni. If the stock coil is removed, this unit is not used. The Jacobs premium "Energy Core" spark plug wires - very low resistance with fully vulcanized, 100% silicone insulation.

Just selecting the installation location for the box turned out to be the toughest part of this installation - There was not a lot of room left under the hood of the Jeep and the unit should be mounted in a location that will not normally be submerged and not directly attached to the engine.

I finally settled on a location on the inside right fender well just below were the Premier Power Welder control box sits. This is very near the stock ignition components and does not interfere with areas were other future upgrades are planned. (Jacobs does offer an optional L-bracket which sits the unit up on end and would allow for mounting in an even tighter space)

Once the mounting location was chosen the installation literally took less than 10 minutes. The four mounting holes were marked with a center punch and quickly drilled with a cordless drill. The unit was mounted with 4 of the included screws, the Trigger Unit was mounted to two of the same screws as Omni Module. The power wires were connected to the battery, the wire from the trigger to the original coil was installed and the wire from the new Jacobs Omni Module to the distributor cap was hooked up. Once we installed the included fuse on the power wire we were done. The engine started and purred like a kitten with the first twist of the key - none of the cranking and cranking that it used to do and no pumping the gas peddle was needed. I was very impressed with the speed and ease of installation - another reflection on the quality design found in the details of this unit.

One great feature is that the entire stock ignition system can be left intact, this is very important for serious off-road use. Now there is a redundant or backup ignition system that can be switched to quickly in the event that anything should ever fail in the field.

My initial driving impressions with only the ignition unit installed (no wires, no re-gapped spark plugs, no cap & rotor) was that it started much faster, ran much smoother (especially at idle and during acceleration) and had a bit better power. One surprise was that now the engine readily revved past the 3000 rpm mark. This dramatically improved the whole freeway onramp experience as well as everyday freeway cruising from 55mph to 75mph.

The initial impression was positive but rather subjective, so we decided to line up a chassis dynometer and do some testing to see if the actual rear wheel horsepower and torque numbers improved. This is were we hit our first snag - finding a chassis dyno! It turns out that they are very rare indeed in the San Francisco Bay Area! Fortunately we were able to find Streetwize Motorsports in Fremont California, and they agreed to squeeze us into their busy schedule.

We decided to test the unit stock, with just the Omni Magnum Ignition unit installed, and then with the Jacobs Wires and with our spark plugs re-gapped to Jacobs Electronics' recommendations (.055 vs .035 for stock). To make sure that we had all of our ducks in a row we installed a new cap & rotor and a fresh set of Champion HD truck spark plugs gapped to the stock setting (.035) before testing. When we arrived we were able to quickly switch the coil wires and pull the fuse on the Jacobs unit - that was all we needed to do return the Jeep to using the stock ignition system!

The first run was almost embarrassing - the 1990 4.2L was rated at 112HP and 210 ft/lbs of torque measured at the engine flywheel. We were taking our measurements at the rear wheels - but I was still surprised at the numbers. On our stock run we measured 71.8 HP at 3200 rpm and 156.4 ft/lbs of torque at a nice low 1800 rpm. We then quickly reconnected the Jacobs unit and with just the Omni Magnum installed we generated 72.6 HP at 3200 rpm and 167.5 ft/lbs of torque - again at 1800 rpm. This was an improvement of about 1 HP ( +1.3% ) and 11 ft/lbs of torque ( +7% ).

Unfortunately we ran out of dyno time before we were able to install the Jacobs wires and re-gap the spark plugs and make the final run so we do not have exact final numbers for you. The next day we did re-gap the spark plugs and added the Jacobs wire set and the seat of the pants difference was very noticeable. It really felt like we gained several times what we did with the ignition system alone. Now the engine not only revs all the way to redline but pulls much stronger the whole way too. We will schedule some more time on the dyno as soon as possible and run the final tests - we will update this review at that time.

Jacobs clearly met their claims of faster starting and smoother running with no misfires.

I would project (based on the initial postive dyno testing and the seat of the pants estimation of the improvement after the new spark plug wires and re-gapped spark plugs were installed) that Jacobs easily achieves and probably beats their power claims in this application. I must, however, emphasize that much of the raw performance improvement was only realized when the spark plugs were re-gapped and the Jacobs wires were installed.

I would love to be able to give a glowing report about improved mileage and while I am sure that if I was driving the same way I was before the Jacobs unit was installed it would have improved, I have been having so much fun with all of this new found power (chirping those big 35" tires) that I could not make an accurate comparison.

Overall I would recommend the Jacobs Omni Magnum Ignition System for the Jeep - Not only do they talk the talk, in my opinion, they walk the walk.