Autolite XP985 vs Autolite XP5405

[Steel City 06]

For anyone looking for a colder spark plug, check out the Autolite XP5405. It is the exact same plug as the XP985, just one heat range colder.

Autolite does in fact have other plugs that will fit the TJ; however, these plugs are not extra-long reach like the XP985 and XP5405, and won't start the kernel quite as far into the combustion chamber as the original plugs.

The only difference between the two plugs is that the XP5405 is designed to dissipate more heat than the XP985.

Note that colder spark plugs should only be used for one purpose, and that is to eliminate pinging due to spark knock/preignition, which commonly occurs on tuned engines, higher performance engines, and engines with forced induction.

If a higher octane fuel doesn't eliminate your pinging sounds, chances are colder plugs won't either. But if it does, colder plugs may eliminate the need to run higher octane and save you a lot of money.

If your spark plugs have soot or carbon deposits on them, colder plugs will only make the problem worse. In that case you will want hotter plugs.

Posting this because I found extremely little information online about colder plugs with the same reach as factory for the TJ 4.0.

 

[pagrey]

Great info. It is difficult to find this info now days, the guides are terrible. Most of them are "this vehicle = this plug" the end. I've had to get different heat range plugs for an old Ford and navigating all the part numbers is pretty difficult even for a common plug.

 

[Steel City 06]

A wee bit toasty. And that coloration is not soot. There is a bit of soot in the exposed part of the threaded base, but all the colored stuff on the insulator and top is hard and metallic-like.

No pinging at WOT with the new plugs yet. Just need to drive a bit east and find a big hill.

 

[Steel City 06]

Well, I can definitely say my pinging at sustained WOT and high RPM is gone. Almost feels like I have a bit more power without the pinging as well, but I couldn't say for sure.

If you're battling pinging, definitely consider colder plugs.

 

[Steel City 06]

To update, still running the same XP5405 plugs without any issues. I am running the K-Fab Suspension Viper coil which makes a more powerful spark, and it does not seem to cause any negative issues with these plugs.

No issues with pinging or detonation, even with a tune and consistently high loads across the RPM band.