Shortly after getting my XJ, I did a full tune up (cap, rotor, wires, coil and plugs). It had champion plugs in it (my fellow technicians at work refer to them as "lawn mower plugs") when I bought it so, that's what I went with and made sure each plug was gapped to 35. It idled pretty good after that............not perfect but, still. After about 15K miles, I noticed the idle getting more and more rough so, I pulled the plugs and found 2 had worn down to a 38 gap and one down to a 40 gap.
That's WAY too soon to be worn that badly.
Up until recently, I've been averaging about 11.5 to 12mpg, even after the tune up. Something needed to be done.
After doing a bit of research and reading numerous reviews I decided to go with NGK V-Power plugs and I must say, I'm very pleased with them.
In addition to a much smoother idle and a notable increase in throttle response, I've averaged about 14.8 mpg for my last 3 tanks of gas.

I've used the NGK's in just about every vehicle I've had and I've always had good luck with them. Been running them in both jeeps for a few years now and no problems.

Whatever problem caused the gap to open that quickly, is still there.

That sounds unrealistically high for only a change of plugs, (sans canning platinum's) Still sounds interesting enough though. I subscribed to this thread, hope that only mails me with posts from here! I keep accurate MPG #'s and am do for an new set, just re-gaped the set I bought in 2011 this winter for the third time.
If the old girl is still sucking oxygen this fall maybe I'll give those NGK V-Power a trial. Do you know anything special about them? (helium cooled, supper conducting?)

Kidding there of course. CF, with high power computers, "materials modelling" is going to take off. Edison needed to test allot of stuff to make a light-bulb. Now that can be done with computers. Watch for batteries, solar panels, conductors...... all down down the line. Being able to narrow down/make new materials without actually needing to build something, then test it will accelerate new materials designs. A whole new "Ball-game!"

I thought you said " a couple of words"

Shoulda said "3 letters". NGK all the way!!

Nothing at all. V-Power is just their branding for a cut in the electrode tip. They're just basic copper plugs aside from that, OE (sorta) in late model 4.0s with coil-on-plug. ZFR5N that we go on about all the time.

Agreed. 0.035" to 0.040" in so little time is suspicious.

How did the old plugs look? Aside from gap.

Yea, I ZFR5N whenever I get the chance. (tiring sometimes). Of course I know exactly what we mean, but maybe you could elucidate some of the less knowledgeable among us what that's about.

I know the v-power plugs aren't anything new...............been around for years and I probably would've been happy with just about any NGK plug but, they were the only type the local parts store had in stock for my XJ at the time and had 6 of.

I've used NGK's in most of my other vehicles including my motorcycle but, this is the first domestic vehicle I've tried them in.

I ran tr55s in all my v8 engines, the best 93 oct non-n2o plug available, imho.


edit: perhaps I should check my plugs. I haven't observed a noticeable amount of mpg loss, but the idle did go from perfect to a little rough lately. I have the champion oe replacements, whatever they are. I wanted ngks, but could not find them when I wanted them. I have about 20k miles on them. I pulled one a few weeks ago and everything looked/specd out ok, though.

I think what Napa sold me years ago are AC. On One highway trip I cleared 21 MPG with my old Renix. Can't be all bad, but I'm ready to try the best.

Oh my god! Get a life ppl! It's just spark plugs! Spark plugs! Most ppl buy any reasonably priced brand, install them and forget about them till the maintenance is due again. And guess what? All of the major brands work just fine. NG effin' K's are not going to be noticeably different than any other major brand. The way some would claim, you put those bad boys in your XJ and you'll be taking down 911's in the quarter. Find something more interesting to debate.

Oh **** guys. Someone asked what people thought of something and they got an opinion.

STOP THE PRESSES AND CALL THE INTERNET POLICE



You're going to do well here, I think.

Glad you're here to help our sorry asses figure **** out!!

What the **** do we know? Your appearance on the scene is manna from heaven.

I don't think he realizes what an "enthusiast" is.

Hard to understand that stuff when you have 2 issues.
One, having a ****-poor attitude and 2 having you head planted firmly up your ***.