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Discussion Starter · #1 ·
I just changed spark plugs in the 4.0l in my '98 TJ. I had noticed a slight power drop-off a while back, just like our '88 LeBaron Coupe (2.5l) does when it needs new plugs. After 29k miles, new plugs seemed reasonable. I bought a set of Champion truck plugs in hopes that they will last longer. The factory service manual specifies 0.035 gap, but the new plugs were gapped to 0.040. I tried bending the side electrode to get 0.035, but it looked like I would risk breaking it before I would get a nice even gap. I recalled that on Mopar 318 V8s, the specified gap was 0.035, but they ran much better with 0.040. I went ahead and installed the plugs with 0.040 gap. Does anyone have experience with running different gaps on the 4.0l? BTW, the old plugs were running a little more than 0.040 gap due to wear.


Another issue, has anyone else found that the original plugs were difficult to break loose? I had to use a 1/2" breaker bar and a fair amount of force to get the plugs loose. I broke the insulator on two of them. I've never had plugs stuck this tight in either cast iron heads or aluminum heads, and have never broken insulators, and I've been changing plugs for 20 years. Granted, these plugs take a 5/8" spark plug socket, so I couldn't use my trusted 13/16" spark plug socket. I used anti-seize on the threads when installing, so next time should be easier. I also spritzed a little silicone spray into the spark plug boots in hopes that they won't be stuck as tightly, either.

Bill

 

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Just curious... and I beg your pardon...but I'm a bit behind on my spark plug technology.....how does a "truck plug" differ from a regular plug? I use Bosch platinums and have had good results for over 40k in one vehicle......I'm trying Bosch +4's in my rice burner Caravan (3.0 Mistubishi)...not much improvement......but I'm looking for the longest lasting installation.
I've run higher gaps on some of my vehicles in the past (before settling with the Bosch platinum) without much noticable effect....who knows? You still have to ask yourself why did the engineers put it at .040 in the first place.....what were their reasons.....would a different gap serve you better due to your specific driving needs?
Yes, I had a hard time getting the OEM plugs out of most of my "30,000 mile plug change interval" engines. It could just be the guy on the lines idea of a joke so he turns up the air on the air rachet when installing them (can you imagine hand threading 800 plugs a day?).

Gary


 
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Discussion Starter · #3 ·
The main difference is that a truck plug has thicker electrodes, and should last longer. I believe that there are other differences. I tried Bosch Platinums in the Mopar 2.5l in our '88 LeBaron with the hope that plugs costing twice as much would last twice as long. Still needed new plugs after 15k miles, so I went back to Champions. We are the original owners of the car, I don't remember having trouble getting the first set of plugs out 10 years ago. Maybe it's a recent issue with UAW.


 
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