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Jacobs Electronics Spark Plug Wire Set for the 5.2L

by Neil Winnemore

Why just do regularly scheduled maintenance when it's such a good excuse to upgrade to performance parts?

Replaceable items such as fluids, filters, spark plugs, wires, tires and brake components are perfect candidates for upgrading. The 1996 Grand Cherokee 5.2-liter owners’ manual, Maintenance Schedule B, recommends replacing the spark plugs at 30,000 miles and both - spark plugs and spark plug wires at 60,000 miles. If your motor is already well maintained, then this frequency is conservative. But if you're always looking for another way to hone your performance edge, then it's a timely opportunity.

Today's case in point - spark plug wires. The subject spark plug wires are from the ignition specialists, Jacobs Electronics. The part number for the 5.2 liter motor is 4007851, this is the 8.5MM Ultra-Fit, Vari-Angle Plug Boots model. Note - the OEM spark plug type is RC12YC, gapped to .035, and torqued to 30 ft. lbs. Make sure any replacements match this specification. I replaced the original plugs with AC Delco Rapid Fires, using the original plug wires, and felt a perceptable difference in smoothness.

Installation

In the strictest sense, no tools are required to change plug wires only. The tools you really need are your spark plug wrench set, plug gapper and leather gloves. It's a real danger zone in there for your skin. Also, think seriously about acquiring a Spark Plug Boot Puller (wrench), pulling the plug boots off is the hardest part of this job. Don't laugh! Here's a great big hint. If you're going to change the plugs or wires, for goodness sakes change them both at the same time. Otherwise it's just twice as much work; don't ask me how I know!

Watch out for the manifold heat shield. Notice I'm pointing with an Exacto knife - which do you think is sharper?

The Ultra-Fits are slightly longer but within one inch length of OEM. The Vari-Angle plug boots come with a factory-prepared 15-degree pre-bend, which can be further bent or straightened. The stock plug boots are straight until they exit the spark plug boot heat shield, then they angle back towards the rear of the engine where the distributor hides. I found it necessary to straighten the Jacobs boots to within 0 to 5 degrees. Jacobs includes complete instructions, even common sense recommendations like - only do one wire at a time so you don't get them mixed up. This sound advice notwithstanding, due to the opposing angles of adjacent plugs, you have to remove two at a time, so pay attention.

Here are some ZJ-specific details:

The stock wire separators are designed to fit OEM 7MM wires. That means it's a tight fit at best to get the fatter wires in.
Don't push on the plastic separators, they snap easily.
Jeep wisely covers the stock wires (7-8 inches long per wire) with corrugated cable shield where they run close to the manifold. While you may be able to salvage them, they will be brittle and break. Do yourself a favor, size it up and buy some new stuff before you start.
You will have to, at least, remove the air intake plenum to reach the distributor.
I'm 6' tall and I still needed a crate to stand on to reach the distributor. (Blame it on the lift kit.)
and take off that rodeo belt buckle, save the paint scratching for the trail.

Finally, Jacobs recommends that "for greater improvement when you install Energy Core wires", increase plug gap by .005".

Results

The skeptic in me thought that if the good wire fairy sneaked in to my garage and swapped in high performance wires, I probably wouldn't notice and just motor happily down the road. After a week with the new Jacobs spark plug wires, I am pleased. It actually cured some low-end hesitation I didn't realize I had and the throttle seems to respond quicker at any RPM. Was it worth it? Absolutely! The slight performance improvement coupled with the extra confidence of knowing I have top quality components is satisfying.

Jacobs Electronics 500 North Baird Street Midland, Texas 79701 800-627-8800

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