best spark plugs for a 4.0 (02 grand cherokee)?

[brdhntr]

i'm going to change plugs for my father in law in the future. i was just wondering what you guys have found to be the best in this application. also, his cruise only works on occasion. when he gets it set it may be fine, or it may fail at anytime. sometimes it won't even engage. it's very hit or miss. any ideas?

[dasbulliwagen]

Being a dealer tech, I have NEVER seen a problem with factory plugs. I have seen problems with other brands, but I'm not sure that it has ever been with a 4.0. I myself love the Bosch Platinums, but I'm sure other people will have better opinions as to what works best, as I don't own a 4.0.

 

As far as the cruise, check the vacuum line going to the cruise module under the hood. The WJ is known for the vac lines going bad, at least the rubber parts. Another thing to check if that is ok is the buttons on the steering wheel. If they have a problem they could cause the problem youre describing. If you have access to a good scan tool, you can hook it up and go into sensors, or inputs/outputs, and try to work the cruise buttons and see if the values change or not. If they don't then you would have an issue with the buttons or the harness, usually the buttons. Good luck!

[jpdocdave]

stick with the o.e plugs. if its a late 4.0 w/ direct ignition (coil on plug) they are ngk platinum. earlier 4.0's like regular ole champion.

[brdhntr]

any idea on the specifics for the plug? the exact plug? i want to be able to tell him what to go get so he doesn't mess something up when he's looking them up. it'll be easier if i can just call him and give him the brand, plug type, and number.

 

i know some plugs work better than others in some engines, as well as different heat levels. is ngk platinum the oe plug? it's on an 02 gc with 4.0.

[CWLONGSHOT]

IMHO, Stick with factory recommended Auto-lite/Champion copper plugs. Ours are old technology, don't try to polish a turd...

 

CW

[aemsee]

stick with the o.e plugs. if its a late 4.0 w/ direct ignition (coil on plug) they are ngk platinum. earlier 4.0's like regular ole champion.

 

NGK yes, platinum no. DO NOT USE platinum plugs in a 4.0L. period.

[jpdocdave]

i was about to go on a rant about the o.e's in the late 4.0 was platinum, but i'm gonna agree w/ everyone else, i got screwed up by an idiot dealer parts guy though, toldme they were platinum, but when they arrived they were regular ngk

[GaruMJ]

Why I shouldn´t use platinum? I just changed mine with champion platinum and it is working fine.

it is a 4.0 1990MJ

[Comanche County]

IMHO, Stick with factory recommended Auto-lite/Champion copper plugs. Ours are old technology, don't try to polish a turd...

 

CW

 

 

:agree:

 

Everytime I think I'll get better mpg or hp with fancy plugs, they foul out prematurely. Stay away from splitfires, v-fires, etc. You could replace regular plugs 2 or 3 times for the price and get way more mileage out of them. I'm not a fan of any platinum, but some people have had better luck with them than I. Stick with regular plugs and gap em right. Also, check inside the plug boots for damage. Sometimes if you pull em off a lot the wire will tug free of the metal connector inside the boot and make an intermittent connection or none at all. The plug wire could look fine but be damaged on the inside.