No experience but I can tell you that platinum plugs were never stock in any Jeep 4.0L, and I wouldn't want to waste my money on them.

returning them & getting NGK's recommended by previous reply

I have had terrible experiences with Bosch Platinums.

That's because all you drive is the Renix junk.

Never used them in a Renix

Lost 28 RWHP on the dyno compared to Champions. Datsun Z with triple Mikunis etc. Wish I had a set of NGKs on hand for that dyno run.

Alfa Romeo 2000 with a driveability problem. Switched from Platinums to NGK. Problem gone.

Honda CRX throwing an oxygen sensor code. Failed Platinum. Put NGKs in and continued on.

The second 2 lead us on a wild goose chase and cost an oxygen sensor unnecessarily and numerous hours with mechanical fuel injection adjustments.

i see that there are NGK nickel and NGK copper available at my local parts store. any suggestions on which one to go with?

The electrodes are Copper with Nickel plating.


Take your pick but, not knowing what year your Heep is, I would suggest NGK ZRF5N if it's '96 or later.



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i've got a 97

ZFR5N

I wonder why the difference between 88 and 91. Higher voltage=hotter, shorter porcilin? Just curious.

87-90 Champion used heat range (9), then in 91 changed to (12), but NGK used the equivalent to Champion 12 heat range (5) from 87 to 2001. Go figure. Porcelain protrusion (heat transfer) may be the difference[?].


Cruiser54 uses heat range 5 NGK's (ZFR5N) on his early 4.0's with no issues that I know of.

OK then. "Drop Kick me Jesus". Prayer; " please don't burn a hole in my piston, please don't go "open circuit" please light the mix"... Amen.

I have to admit after many years of using Champion copper core RC12LYC and other Champions with a bit lower heat range exclusively in my OBD1 Hesco stroker, I tried the NGK FR5-1 plugs a couple of years ago and was impressed. The stroker has a Mike Leach header, 99 intake, 62mm bored throttle body, dual 2.5" exhaust, and all the other bolt-on stuff. The NGK's really smoothed out the idle even with the RVOB cam. I'm about due for new plug set, and am thinking about trying the ZFR5N plugs after reading this thread. Heat range, plug gap and reach all compatible with the FR5-1 plugs? I've always used a .040 gap with this engine. What are the differences if any between the two? Or should I just stick with the FR-5 plugs? Thanks in advance for any advice.......

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