7ate9

I've heard just a good old copper plug works well
Can someone give me a part number # or recommend a good plug?? This is for my 90 renix 4.0 Ho i6 aw4
Thanks for the help

Firestorm500

I don't like Champion or Fram. Get Motorcraft if you can. Parts stores have the numbers.

7ate9

Just ask for motorcraft copper plugs for a 4.0?
Is this the best plug for our jeeps??
Thanks again

Firestorm500

You said you wanted copper.

I use NGK iridium plugs in mine. 100,000+ miles. Put 'em in and forget 'em.

7ate9

Thanks I'll check those out too,just wanted to know what the best plug was I guess there's not a whole lot of difference it's just preference?

mschi772

There is nothing better than NGK ZFR5N or Champion RC12ECC gapped to 0.035" in a stock 4.0. These were the factory recommendations. I would do Champions if I were you. If you're doing a full tune-up, I recommend NAPA--cap and rotor with brass contacts, Belden wires, and lots of people forget to do their fuel filter at tune-up time, so remember to change that, too.

Don't do platinum or iridium unless you're willing to do other changes to your ignition system to better deal with their lower conductivity. Don't gap any larger than 0.040" unless you're willing to do other changes to your ignition system to ensure spark will reliably jump a larger gap.


My personal setup is:

MSD coil
Magnecore KV85 wires
Kelley's Work in Progress (aka 5-90) battery cables
Autolite iridium plugs gapped to 0.050"

Firestorm500

Well as they say, YMMV but spark plug technology has moved on since the 1970's lawnmower-type plug for engines.

My 4.0s never skip a beat with the NGK iridiums. I have absolute confidence in them. I have low to zero confidence in conventional Champions. I have had too many fail when they were still very young. Some were defective right out of the box.

Fred/N0AZZ

Dam I must be dumb as I still run lawn mower plugs in my race car that has over 10x the hp of my 4.0.

SomeGuy138

Never had a problem with Champions and I have used them in ever Chrysler I have owned.I even had a 1986 laser XT that would eat plugs up like crazy but it ran like crap with every other plug I tried in it other then Champions so I went threw a lot of Champions.I bet I used over 40 plugs in the car in the few years I had it and never had a out of box crap one.Plus there dirt cheap.

scottmphoto

I also run Champion coppers and haven't had a problem with them in either of my XJ's. They are pretty much what the 4.0 was deigned to use.

Firestorm500

Switching over to iridiums might help you win more races. If your ignition system can handle them.

Assuming your rules would allow them.

kyledye25

Am I wrong in saying this? But last I knew copper plugs have the best strongest spark. Then platinum plugs have lesser of a spark, not by much, but last longer. Then iridium plugs last the longest but doesn't have the spark of the platinum or copper. I run copper plugs, champions to be exact, in both my 4.0 Cherokees. Zero issues.

mschi772

Correct...mostly. Copper plugs have the best conductivity but least durability.

Iridium has the best durability and has a very small electrode which can be beneficial for flame kernel generation. It is slightly more conductive than platinum, but still significantly less conductive than copper.

Platinum is more durable than copper, but less durable than iridium. Platinum is the least conductive of all three.


I use iridium with a large gap in order to maximize flame kernel generation for the, theoretically, best burn possible. I can do this because I have a powerful enough coil to ensure a dependable spark through the less conductive material and across a larger gap and wires that are insulated enough to handle that power.


If I re-did it, I'd probably just use copper plugs and check and regap them periodically.

I used Champion coppers with Belden wires and a stock coil in my old 96 XJ, and it ran fantastically.

Turbo X_J

Stock ignition and plugs from the factory have run 15 years/100k miles no problem, it don't take much. Even if the gap is .250" they still start and run every time.

7ate9

So I'm going to get some of the champion copper truck plugs and I was wondering does the Cap/ rotor have to be copper as well??I think I'm running bosh iridium with the set of wires from Summit that say ford on them didn't realize that, but they say they're for 4.0