What are the best spark plugs for a 90 Cherokee 4.0L Inline 6?

[ltkaknm]

I posted a few problems with my 90 Cherokee, and I just replaced some Autolite Platinum plugs with Champion standard and all of my problems have disappeared. I did not know that the brand of plugs could be so important. If anybody else has problems with stalling or bucking I would check the plugs first.....sounds obvious but sometimes you just think it is more complicated than it is.

LTK

[MogifiedXJ]

Standard NGK or Densos is what I always use in my 4.0l.

[90xj06]

illhave to go check what i have in mine. i thought plugs where plugs

[RichP]

The 4.0L is just very happy with the champion coppers.

[TiRod]

I treid Bosch single Platinums for 20k, then started delivering rural mail. The electrodes had worn down into the insulator, which led to hard starting. I switched to NGK's and had no further problems.

Now whether it was worn out plugs or not, hmmmm. But platinums are not required for vintage 4.0's. Later models with OBDII seem to prefer them - but is it because they throw less misfire codes, or they actually work better?

[90xj06]

iv gone and checked my plugs and i do have champion now im happy. :)

[Michaelarchangelo]

Ive always run copper plugs, even if it called for plat plugs. The only real benifit you get from plat is that they can go 100k miles (have you ever seen plat plugs that went that long?). I figure the plugs are a cheap wear item, and I change them out once a year, since that is where many firing problems start.

[Pioneer84]

NGK FR5's Here

[bewilderedbeast]

I've run lots of different plugs, but I prefer either NGK or Champion.
Do a Google search on the differences bewteen platinum and copper plugs, you may find what you learn interesting.

[langer1]

Champion Truck plug 4430 Has always worked best for me in the 4.0L

[laredo]

I run regular Autolites.A dealer I know that pretty much all they sell is Cherokee's says that's all he'll throw in them.I had Platinums and they told me to take them out of there.I always assumed that a "better" plug would make it run better but that's not the case.

[hotrodXJ]

I've seen quite a few problems caused by non-oem plugs. Even as soon as a day after changing to non-oem plugs, they come in with an issue with them. This does not only apply for jeeps. I've worked at dealers for Jeep, Buick, Subaru, Dodge and Mazda. The only make that I havent seen a problem with non-oem plugs installed is a mazda... and thats because it seems mazda owners don't change their plugs.
Of course I have my Champion rc12lyc's installed in my jeep.

[martin]

I use the stock champions in my 88 XJ 4.0 engine. I buy them at the dealer even though I can buy the same Part number. When I get them at a dealer the box has MOPAR printed on it, along with the champion stuff.

I know chrysler puts requirements on Champion for the plugs that are not on the ones you buy at the parts store. I figure paying $2.50 vs $1.50 per plug is a small price to pay for the value added by chrysler.

I also get my cap, rotor and wires at the dealer. They are good stuff and cost less than what discount big box parts store wanted.

[soarhead25]

I believe the whole reason behing platinum plugs is that they give you an extended service interval, not actually any better performance.

Auto manufacturers exploited the platinum plugs to their benefit. They could advertise to the consumer an unheard of 100k mile tune-up! What a selling advantage for them. What the consumer didn't realize is that when buying that transverse engine minivan with the engine half way under the dash, is that the tune up had to be done from underneath AND you had to be double joited in your elbow & wrist. Platinum plugs was the answer to this problem-who was going to buy a car that had to have a $250 tune-up every 30k miles? Nobody.

There is no reason to run platinums in the 4.0 simply because of the spark plug access. Even if you did run platinums, it would be wise to R&R them every 30k to clean/gap/apply anti-seize to prevent seizing.

Just run the standard resistor champions-
Replace them every 30k miles, gap them properly, use anti-seize even if the cylinder head is not aluminum, use a spark plug socket WITH the rubber insert, torque them properly, and as straight on as possible to prevent an unknown cracked ceramic insulator that could cause drivability problems. Always have it quiet when torquing your plugs so you can listen for a "tink" that might be you cracking your ceramic. Use dielectric grease sparingly in the wire boot, don't use oily hands when handling the new plugs, and for petes sake, change out your valve cover gasket if it's leaking oil into your spark plug recess and onto your wires!

Chrysler did extensive dyno/performance/emission testing with these plugs for that engine and there is no good reason to circumvent their efforts.
I also recommend autolite/motorcraft for ford, and ac-delco for GM, NGK/ND for imports, and Bosch for european-(in general, but always the OEM plug).
And I'm just not a believer in spark plug cross referencing.

[Rob Mayercik]

What IS the torque spec for plugs, anyway? I've never bothered to look it up.

I can honestly say I've never torqued a spark plug (heck, until I bought my rock rails back in June, I didn't even own a torque wrench). It's been a while since I did a set on either my XJ or my old Omni, but I use the method my father taught me:

1. Put the little gasket on the plug, and apply a little antisieze to the threads.

2. Install the plug hand-tight. I usually put the plug in the socket and use the socket and extension to hand-tighten since my hand doesn't fit down in the cubby where the plug sits. When starting to insert plug, use caution so as not to cross-thread.

3. Use wrench to tighten about another 1/8 to 1/4 turn. This isn't so much tightening as it is "snugging it down".

4. Repeat on next plug.

I have never broken a plug, and never had one back out on me. They're still snug when I go to replace them, though I have never needed more than a token amount of force to loosen one.

[soarhead25]

When I said torqueing them, I meant tighten properly, and I think the taper seat is 1/16 turn past fully seated, and compression washer is 3/4 turn past fully seated. You bring up a great point I forgot to mention-always install by hand.

[Phager]

After reading this thread, I decided I couldn't go wrong by picking up a set of Champion plugs to see if it might remedy my hesitation issue. My question is, what is the proper gap for a Renix 4.0L? I know it's kind of a stupid question, but I don't have a service manual yet (Financial aid comes in on the 8th and it's earmarked for a manual and membership) but I'd like to get these plugs in in the next couple of days.

Thanks in advance!

-Pat

[martin]

I am too lazy to walk out to my 88 XJ and look but I believe it is 0.035. Go out to your XJ, open the hood, look at the white sticker on the cowl, the spark gap should be listed on that "emisssions" sticker.

[Phager]

See, now why didn't I think of that? I mean, I know the emmision sticker is there and all the tune up info is on there, and yet for some reason I completely spaced that fact!

Thanks for the reminder Martin. And for future reference on (at least) my '87 the acceptable gap range is .033 - .037, so you were spot on!

Thanks again

-Pat

[black89xj]

I can concur that the champion plugs seem to give the best performance and life in the 4.0. I have a 1989 Xj with a 4.0, AW-4, 326,000 miles. The best plugs have been the Champion truck plug, champion number 4430. My current set has about 50,000 miles on them. When I checked them in the spring, after about 18 months, they didnt even need cleaning/regapping! The next best is the Champion standard copper, RC9YC.

I have used bosch platinum and autolites with poor results. Would not use them again. I have not tried NGK.

[gradon]

I just installed double platinum autolites, Accel cap, rotor, coil, and Magnecor kv85 wires and my 94 is running better than ever! She really impressed me tonight. My Champions were still in good shape, but I wanted to do it all at once.

[anodyne33]

I replaced mine with glow plugs and run jet fuel. ;)

[mikeny59]

private or commercial?!?