BigRed93xj

Ok so I've been searching through all the threads on here trying to find the best spark plug, wire, and cap/rotor set-up for my 4.0 xj. Here's what I think,

Spark plugs- Champion (However I don't know which kind to order, the most expensive is the double platinum, then there's the single platinum and truck plug. Which one run's best in our rigs?) I'll probably be upgrading to the MSD offroad ignition in the future if that matters.

Wires- So I wanted to go with the SummitRacing 8mm wires. I'm running 7mm now, is there any difference in running the larger wires instead?

Cap/Rotor- Ok so I read on here that brass terminals are the way to go. So I found the Gold/ Distributor cap and rotor kit from Autozone. Here are the specs for it- (Exceeds OE specifications. Brass blades in the precise size with radio frequency interference suppression coating, ensures accurate spark gap to eliminate RFI. Corrosion- resistant stainless steel contact springs to maintain proper tension). Would this be good for my XJ?

Ok guys what do you think, would that be a good set-up or should I try something different. Thanks guys.

BuckB91XJ

Just did a tune-up on my XJ a month ago. I installed the Duralast Gold Cap and rotor kit, regular old Duralast 7mm wires (the come with a lifetime warranty) so if they ever go bad, bring in your receipt and you get a new set free....and the regular old OEM Champion Sparplugs for the 4.0. The Jeep runs great.

troy fritz

I always run the regular Champions. Never failed me yet. They are a good plug. And 2xs on the 7mm lifetime wires and cap n rotor.

BigRed93xj

What about the Champion double platinum plugs? Would there be any benifit from them? And would running 8mm wires hurt anything?

lifted1994xj

I just did a tune up on mine got regular champion plugs and car quest wires. It runs great. I read in JP magazine that ignition mods don't do anything for the 4.0 because the engine is already so leaned out extra spark won't do anything for it.

BigRed93xj

Oh ok, like before I mentioned I wanted to get the MSD offroad ignition which makes the spark plugs fire twice under 4000rpm. They say the purpose of this is to make sure all the fuel is burned off. Would this mod be a waste with my 4.0? Its like $300 bucks so I won't get it if it's not going to do anything... Any thoughts?

mike albo

I have all Napa life time.I am useing bosh plugs not platinum though the 4.0 don't need them

whowey

No advantage to you whatsoever as long as you have not done a bunch of other things.

Carbs by nature run rich and the big CFM carbs are just worse. So they need the extra heavy spark or extra sparks to get the fuel all burnt. But your Multi-Port, computer controlled ignition runs pretty lean to begin with.

Also no need for the bigger wires, your stock system isn't putting out enough voltage to derive any benefit from them.

lifted1994xj

If you want to get a little more spark JP magazine says that the stock ignition will allow for a 0.045 spark plug gap no problem. The only things that they say really for extra power are cold air intake, cat back exhaust and aftermarket header

sandstone

Platinum plugs just increase their gap more slowly over time, thus they "last longer." I find them not worth the money and just stick to regular Champions.

Jamie57

Absolutely no fuel delivery or combustion system works 100% otherwise we wouldn't need catalytic converters. You guys do know how they work right?
So anything we can do to increase the strength of the spark WILL HELP!
And if we can lengthen the time of the spark that too will help "Burn" fuel and help increase both power and mileage.
The MSD system will help but you have to balance the cost of the system to the benefit derived from it. That is a decision only you can make after some research on your part.
The fatter wires don't need higher voltage to do the job they are designed for. They are designed to allow more voltage to the plug with less "Leakage"
Electricity is like water and will take the path of least Resistance. If you have a marginal plug under compression and a wire that will "Leak" the voltage it's carrying to ground, guess where the majority of that voltage will go.
I can't count how many race engines I've helped get those extra 2 or 3 tenths in the quarter by upgrading the ignition system to quality parts.
We've got to stop believing all the info we hear without doing a little research on our own.
Here is another way to figure this. If the MSD and Fatter wires were just bogus hype don't you think all the racers would have caught on by now and stopped using them?