Spark Plug Gap Confussion?

[Jeep-I-Joe]

On the hood I see the spark plug gap as 0.040. Haynes states 0.045. I've had cars and trucks that perform better at gaps much different than the recomended gap setting. Does anyone know the optimum gap for the 3.7 Liter? Please, don't spin off into another copper vs. platinum tiraid.(argue)

 

[ridenby]

On the hood I see the spark plug gap as 0.040. Haynes states 0.045. I've had cars and trucks that perform better at gaps much different than the recomended gap setting. Does anyone know the optimum gap for the 3.7 Liter? Please, don't spin off into another copper vs. platinum tiraid.(argue)

I use 40 with copper.

 

[LibertyTC]

Go with the hood sticker.
Once the gap is wider the Kj starts to run worse.
Most replace plugs every 20-30000 miles, and the gap is worn (larger) then.
Fresh plugs with the gap set correctly, seem to have a smoother idle as well.

 

[Jeep-I-Joe]

Go with the hood sticker.
Once the gap is wider the Kj starts to run worse.
Most replace plugs every 20-30000 miles, and the gap is worn (larger) then.
Fresh plugs with the gap set correctly, seem to have a smoother idle as well.

I had the dealer do a tune-up when I had her checked out. The idle is not as smoth as I would like. I am really trying to smooth out the idle. Has anyone tried a gap tighter than 0.040?

 

[Dave]

Mine is an 05 and the emissions sticker under the hood says .040 and that is what I used when I changed my plugs. (actually they were pre-gapped but I double check plug gaps anyway)

Dave

 

[osufans]

i guess it all depends....on another car i used to own, many owners would increase the gap up to the point the engine would start to stutter, then back it off a few thousandths...with the thought that a wider gap makes a hotter spark, which results in increased efficiency, which would equate to more HP (not really making more HP, but helps you to get all you can.)

they would use copper plugs too, and replace them every 20-30K.

my autolite double-plats came pre-gapped at .044", which i didn't bother to change to .040" that the hood specs. not sure about the ignition system on the Jeep, but my other car was a Ford Focus SVT, and even on the factory wires, owners could gap up to .060" with no issues.

heck, just after i bought the jeep i checked my plugs, and they were gapped to .070"+ from being worn down. jeep was still running fine, just a slight stutter under load.

 

[67Customs]

The Autolite sprak plus that are recommeneded for the 3.7 is gapped to .035. I had to gap them to .040. I wish they made them pre-gapped to .040.

 

[LibertyTC]

In your tune up did the dealer perform an emission service/throttle body cleaning??
How many miles on your KJ?
De carbonizing/ clean fuel system/throttle body gets the best result for a smooth idle.
I also use a bottle of Chevron Techroline (TECHRON) in a half a tank of gas, with 1 hour highway run, keeps things clean twice a year.

 

[Jeep-I-Joe]

wider gap makes a hotter spark, which results in increased efficiency, which would equate to more HP (not really making more HP, but helps you to get all you can.)

Is that true though? Is a wider gap preferable? I always thought it was more important to ensure the spark with an optimum gap than to go for intensity. From the optimum gap, is it better to be wide or close? Obviously it is better to be at the optimum, but...

 

[LibertyTC]

There is no need to increase spark as the Liberty coils already provide a hot spark.
Chrysler would have tested different gaps, and found the best gap for the motor/ignition.
One thing is certain as the gap gets too large it will run like crap, and worsen fuel economy.
Anyone want to burn the plugs or worse top of piston?

 

[Jeep-I-Joe]

In your tune up did the dealer perform an emission service/throttle body cleaning??
How many miles on your KJ?
De carbonizing/ clean fuel system/throttle body gets the best result for a smooth idle.
I also use a bottle of Chevron Techroline (TECHRON) in a half a tank of gas, with 1 hour highway run, keeps things clean twice a year.

I'm sure they didn't break it down like I would. They probably sprayed some throttle body cleaner and moved on. I'm not going to take it back to them. I'm going to get in there and do it right. The only way to make sure it is done right is to do it myself.

 

[Jeep-I-Joe]

One thing is certain as the gap gets too large it will run like crap, and worsen fuel economy.

That's what I always understood to be the case.

 

[ridenby]

At first plug change I did,about 130,000m,plugs had very little of the center electrode left,outer one was wore back a good 1/16th of inch,gap looked like a mile,found it amazing that it still ran. Have read that ignition does not put out enough juice to run big gap,multiple electrodes,after seeing those NGK's I took out,just don't know.

 

[LibertyTC]

The Kj does have a hot ignition, which is why it eats the gap fairly quickly on all the plugs.
This means change the plugs about every 30k miles and restore the correct gap= good fuel economy and a have a "Happy Jeep"

 

[Jeep-I-Joe]

The Kj does have a hot ignition, which is why it eats the gap fairly quickly on all the plugs.
This means change the plugs about every 30k miles and restore the correct gap= good fuel economy and a have a "Happy Jeep"

It's good to hear that the ignition is hot. Does it handle a miltiple electrode well?

 

[LibertyTC]

It's good to hear that the ignition is hot. Does it handle a miltiple electrode well?

As in V-power and this sort of product?
Stick to what others have said, stock NGK plugs or Autolite Platinums.
You are not going to gain any extra horsepower from plugs, all you are doing is igniting the fuel..use what is known to work well and not cause codes to appear.

 

[Ry' N Jen]

I called the Chrysler dealer today and asked them about the spark plug gap for the NGK
Platinum plugs I bought...
(According to the instructions on the NGK plug carton, it says not to regap the plugs!)
The mechanic I spoke to at Chrysler said to just install them without re-gapping them!

 

[LibertyTC]

Mechanic may be correct. The NGK's should come already gapped at .040
Still worth checking though.

 

[riptricket]

I run champion platinum in mine and they are gapped at .044 so i change them to .04.

 

[Jeep-I-Joe]

Mechanic may be correct. The NGK's should come already gapped at .040
Still worth checking though.

I checked the plugs that the dealer installed during the tune-up. I too thought NKGs came gapped at .040. Even though this is the case, I have always been in the habit of checking the gap when I install. If the technician had been in the same habit, he would have realized that these NKGs were gapped at .030. I re-gapped the plugs to .040. Jeep is running much smoother now. I feel better that I know for sure the gap setting. I, also, checked the throttle body. Not a lot of carbon. I think the gap setting resolved the rough idle.