SWT-XJ

I feel like the 4.0 engine I have has more in it. I am suspecting that the ignition system is just a little bit flaky.

What can I do that makes sense on this 4.0 I6 that is worth the expense?

Or do I just stick with stock wires? It's probably not running the original wires, but it has been a while...

Roler

Fancy sparkplug wires will add very little imho. But if you do, buy red ones...

XJlimitedx99

Years ago I bought "Kolak's Ignition Kit" from someone who goes by the username Kolak on Jeep Forum. He is/was a very prominent member. It came with 8.5mm Magnecor KV85 wires, as well as an MSD ignition coil, cap, rotor, and plugs. Its claimed you can gap the plugs to 0.040" with this setup, which is really a very marginal increase and won't get you much. If you really need to spend money on it like I apparently did, you can. Probably wouldn't recommend it.

Ralph77

I got rid of the coil rail in my '00 and did the coil mod.
I did it thinking it makes maintenance and diagnosing a no spark issue a little easier.
I never really understood a high performance coil in an XJ.
I just used a Mopar coil for a JK for the mod.
That being said I did use 8mm spark plug wires.
Don't ask me why cause I don't know.
But they had to be black.
Not a paint my valve cover or diff cover a bright color type so....
LOL.

RockyMtn96XJ

Good quality wires with low resistance, good internal shielding to prevent electrical interference with other electronics (think AM/FM signal) and sufficient outer insulation is what matters. Then if you wanna add more spark from a coil or cap & rotor, go ahead. Just make sure you get wires that are suitable for the extra spark. if that means you need thicker wire, then so be it. Not sure if you'd see gains, aside from MAYBE fractional mpg increase from the POSSIBLY more efficient burn, but you might if your current spark setup is faulty.

UKXJ

Like most things, if they need replacing, may as well upgrade - if it's not going to cost too much more.

RockyMtn96XJ

Not to hijack, but i have to rebuild my motor due to a major oil leak that happened very quickly on the highway, obviously causing internal damage and loud noises. Like UKXJ said, why not stroke it while Im at it....?

SimpleDad

Are you going to take the valve cover off so you can put larger size looms? I like stock size because it's simple to run. I went with the UNITED MOTOR PRODUCTS 27625 tune up kit on Rock Auto. It was fairly cheap, fits in the factory wiring looms, and is kevlar reinforced in case my wires have to take a bullet.

RockyMtn96XJ

Loom schmoom. Hahaha. Unless you like it looking clean and tidy under the hood. I did away with mine a while back.

redmuck

Summits red 8mm wires, just gotta put them on.

That Jeep Guy XJMJ

I'd side with a "cold air intake" from Amazon for a performance upgrade before I spent beyond a stock price range on fancy plug wires for a factory 4.0

97grand4.0

Years ago I had a 67 skylark with a Buick sb 300 in it, dual exhaust, big accel coil, valve job with new valves and springs, 3 spd manual with hurst on the floor. drove it cross country for a couple years. At one point my brother worked for an electronics guy and I made some solid core plug wires. Yes, solid wire core. No shielding. Well, the radio really suffered, as well as anyone’s radio within a block or so, but boy was the spark hot and it did make a big difference.

UKXJ

That's why when copper core wires were the norm, radios had a bunch of suppressors.

97grand4.0

lol. FM wasn’t TOO bad but forget the AM.