Novak Conversions Jeep Wrangler TJ radiator

Can new spark plugs really make a difference?

Lilbomb

Lilbomb

TJ Enthusiast
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Oct 10, 2018
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155
Location
Reno, NV
I'm going to answer my own question with a resounding YES!

So I bought my Jeep with 142,000 miles on it. Did the usual oil change to start and then transmission fluid and transfer case fluid. I've been driving it for a few months now and it seems to run great. This past weekend I decided to replace the spark plugs and WOW.....it runs soooo much better. The throttle response increase was pretty incredible. It seems to rev up faster and just all around run better.

The plugs that were in it were Champion and they look like the originals but I don't know for sure. I have attached photos below. They seem to be burning good but the one thing I noticed was the gap seemed really big. I installed the Autolite XP 985 per recommendations on this forum and the gap on those was much less. I also noticed that the spark plugs were VERY easy to remove, I did not need much force at all to break them loose. That leads me to believe they were not the original plugs but who knows.

Anywho, I figured i'd post up about my experience just in case anyone is not sure if they need to or should change their spark plugs. I would recommend it if you don't know the last time they were changed. The Autolites were $7 per plug and super simple to replace. My next endeavor will be the wires. Someone put some aftermarket ones on it, not sure what kind but I know they are not stock. I read that the Mopar ones are the way to go so I will be getting those and installing them in a few weeks.

Hope this helps!

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Also the electrodes on some of them were "slanted" or just burned up I guess. The photos are not the best but that probably had something to do with it.
 
I bought the same plugs a few weeks ago and had every intention to install them. Looking forward to hopefully putting them in this weekend. No complaints about how the Jeep runs at the moment, but I don't know when or if they were ever replaced.

Next on the list after this is new oil for diffs, transfer case and transmission because again, I don't know when it was last done but certainly hasn't happened in the past 40,000 miles or two and a half years.
 
Very nice. I installed double-platinum APP985s after I bought my 2000 and have been very happy so far. Curious how much longer the iridium plugs last.
 
Autolite, for one, is not even exactly sure how long Iridiums last but over 200k miles is known so far. A friend of mine works in their training/education department and Autolite installed iridiums into his car and after they reached 200k miles they put them under an electron-scanning microscope and no wear was observable. Actually I can't say they still don't know, that was 5 years ago when he told me that.

So far as if new plugs can make a difference, yes but only when the old plugs are worn out. If the existing correct model plugs are in good condition, even installing one of the gimmicky "performance" spark plugs won't make any difference at all. :)
 
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I noticed a much smoother idle when I replaced mine at 92k miles. Gaps on what I assume were the original plugs were all over the board. I went with Autolites APP985s
 
Jerry Bransford said:
Autolite, for one, is not even exactly sure how long Iridiums last but over 200k miles is known so far. A friend of mine works in their training/education department and Autolite installed iridiums into his car and after they reached 200k miles they put them under an electron-scanning microscope and no wear was observable. Actually I can't say they still don't know, that was 5 years ago when he told me that.

So far as if new plugs can make a difference, yes but only when the old plugs are worn out. If the existing correct model plugs are in good condition, even installing one of the gimmicky "performance" spark plugs won't make any difference at all. :)
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What's the perfect spark plug for a 2000 TJ 4.0? 120k miles
 
I'd go with APP-985s since the 2000+ 4.0s use a distributorless rail system wherein the sparks fire more often, I think for emissions purposes. Correct me if I'm wrong. In any case, the general consensus is double-platinum APP-985s or the iridium plugs like the OP used. Careful not to get the AP-985s, which are for pre-2000s with traditional distributors.
 
EROCK said:
I have the rail.. no distributor cap.
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There are three widely recommended plugs that are known to work really well for your engine. The double-platinum Autolite APP-985 and Champion 7412 will both perform well for somewhere around 100k miles. Autolite's XP-985 iridium plug has been shown to perform well for at least 200k miles. There are others but these three are all safe good choices.
 
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Jerry Bransford said:
There are three widely recommended plugs that are known to work really well for your engine. The double-platinum Autolite APP-985 and Champion 7412 will both perform well for somewhere around 100k miles. Autolite's XP-985 iridium plug has been shown to perform well for at least 200k miles. There are others but these three are all safe good choices.
Click to expand...
Just ordered the XP-985s. Thanks
 
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superduty said:
What about for the pre 2000?
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Single platinum Autolite AP-985 or Champion 3034 also good for 100k miles, or the 200k mile Autolite XP-985.

Actually the same plugs recommended for the >2000 model 4.0 engines can be used in older engines too with distributors. You just can't use plus like the AP-985 or 3034 in 2000 and newer distributorless 4.0L engines without experiencing problems like backfiring, misfires, etc.
 
Lilbomb said:
I'm going to answer my own question with a resounding YES!

So I bought my Jeep with 142,000 miles on it. Did the usual oil change to start and then transmission fluid and transfer case fluid. I've been driving it for a few months now and it seems to run great. This past weekend I decided to replace the spark plugs and WOW.....it runs soooo much better. The throttle response increase was pretty incredible. It seems to rev up faster and just all around run better.

The plugs that were in it were Champion and they look like the originals but I don't know for sure. I have attached photos below. They seem to be burning good but the one thing I noticed was the gap seemed really big. I installed the Autolite XP 985 per recommendations on this forum and the gap on those was much less. I also noticed that the spark plugs were VERY easy to remove, I did not need much force at all to break them loose. That leads me to believe they were not the original plugs but who knows.

Anywho, I figured i'd post up about my experience just in case anyone is not sure if they need to or should change their spark plugs. I would recommend it if you don't know the last time they were changed. The Autolites were $7 per plug and super simple to replace. My next endeavor will be the wires. Someone put some aftermarket ones on it, not sure what kind but I know they are not stock. I read that the Mopar ones are the way to go so I will be getting those and installing them in a few weeks.

Hope this helps!

View attachment 73716

View attachment 73717

View attachment 73718
Click to expand...
Those plugs have a beautiful brown color indicating a nice healthy burn and a good fuel air mixture
 
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EROCK said:
Hmmm I wonder what the gap is "supposed" to be on the XP-985 for a 2000 TJ?
Click to expand...
Also I should mention. To this day I have never had a "pre-gap" plug actually have the correct gap it's suppose to. That includes these plugs. I use these same ones for my boat motor and everyone is a different gap every time and yes I'm aware you have to adjust this plug with the special tool that doesn't put pressure or touch the center.
 
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