Spark Plug Weirdness

[2K6 LJ]

Hi there! I'm new to the forum and wanted to ask some questions about spark plug "finickyness".

I bought my 2006 LJ Rubicon last year in October. We flew out to Florida from Arizona to pick it up and drive it back. It's been great up until yesterday. I decided to change the spark plugs because I was noticing some power loss and very crummy gas mileage. (10-12 mpg)

I switched them out with Bosch 9656 Iridium spark plugs (pictured). After switching out the old ones (pictured), it ran really nicely for about five minutes and started running really crappy. It smelt like it suddenly began running REALLY rich and sounded like it was thinking really hard about stalling and the check engine light began to blink. I immediately shut it off as I didn't want to do any damage. I was getting P0300 and P0118. I changed out the engine coolant temperature sensor this morning, but no difference. It may also worth mentioning that I did a coolant flush and put in a new thermostat before summer hit. My rationale was that since I live on the surface of the sun and don't know if it's ever been switched out, maybe I would try doing a little cheap preventative maintenance with a 180 degree thermostat. (It still gets up to about 212, which isn't overheating, but it kind of feels like it might be trying to creep up a little when pulling some of the hills leading up to my house.)

Anyways, it isn't my daily driver; it's just more of a toy. It is our second jeep; my husband bought his JK in 2014.

I haven't plucked out the new spark plugs to test them, which probably would be a good idea. I'm half tempted to stick the old ones back in because before I put the new ones in, there was a little power loss and bad gas mileage, but nothing close to what it's doing now. But, with as old as those are, the gaps on those are anywhere between 0.060 and 0.085!

Any advice or suggestions would be greatly appreciated!

Thanks for reading!

 

[JKP]

Bosch don't usually run well in the 4.0. Not familiar with the double Iridium ones though.

Go with the NGKs that came in it, or Autolite 985 if you use reg plugs.

Or use double platinum APP985 or XP985 Iridium if you want long life.

 

[Jerry Bransford]

Generally speaking, Bosch plugs don't work well in our Jeep engines. It's a heat range issue. I'd switch to the Autolite XP985 which is also iridium but it works well for our 2.5 and 4.0 engines.

Also replace that 180 degree thermostat with the proper 195 degree version the computer is programmed around. Not to mention your engine won't run any cooler in your hot Arizona conditions with a 165 or 180 degree thermostat.

 

[JKP]

Also, the 180 deg thermostat might cause problems if it ever gets cold there. The computer is expecting it to get to normal temp in a certain amount of time. 210 is about right where the gauge should read.

 

[L J]

Hi there! I'm new to the forum and wanted to ask some questions about spark plug "finickyness".

I bought my 2006 LJ Rubicon last year in October. We flew out to Florida from Arizona to pick it up and drive it back.

welcome to the site

Any advice or suggestions would be greatly appreciated!

I'd start with the easiest/inexpensive "fix". Buy some NGK (3459) ZFR5N plugs which are the NGK aftermarket equivalent of the OEM MOPAR/NGK SP000ZFR5N (check for or set the correct gap). That will at least give you a baseline to start with.

* I am on my second set of the Autolite XP985 plugs because I get them for ~$1/plug with rebate but they don't last nearly as long as I would have thought.


Also while I doubt it's related to this issue the correct thermostat is a 195⁰. The lower temp thermostat doesn't help the engine run cooler because once it's open the engine is going to run at the same temp as a 195⁰

 

[JMT]

Generally speaking, Bosch plugs don't work well in our Jeep engines. It's a heat range issue. I'd switch to the Autolite XP985 which is also iridium but it works well for our 2.5 and 4.0 engines.

Also replace that 180 degree thermostat with the proper 195 degree version the computer is programmed around. Not to mention your engine won't run any cooler in your hot Arizona conditions with a 165 or 180 degree thermostat.

This^^^