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Old 06-15-2014, 04:36 PM   #1
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My family has two TJs, my 2000 and my dads 97, both stockers with 4.0 - just had to run out to town and took my dads TJ, and I noticed that it has a lot more pull and speed than my TJ. I drove the same hills that I drive with my TJ, and his easily did them in a gear higher than mine.

I'm leaning toward a VAC leak because I have a strange idle from time to time, as well as a fading in heat when I get on the gas compared to when I'm idling.

Am I just going nuts? I feel like my TJ should not behave that much differently

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Old 06-15-2014, 04:38 PM   #2
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Gearing, condition, quality of cat. are a couple things that could cause a difference. When's the last time you had a tune up?

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Old 06-15-2014, 04:44 PM   #3
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Did the gearing change from 97 to 00? They're both stock sports. Same tire size too! I got this Jeep a year ago and have not done a tuneup, plugs looked good last I checked, fluids changed regularly, what are some other things to do for a tune up? I know everyone's definition is a little different.
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Old 06-15-2014, 05:02 PM   #4
Knows a couple things...

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You're going to need to tell us the axle ratios for both your and your dad's Jeeps, as well as the transmission types and tire sizes for each. Jeeps came with various axle ratios and yes one of the available axle ratios did change after the '97 model year.

Your axle ratios can be found stamped into the steel tag that should be on the axle differential cover. The below tag is indicating a 3.73 axle ratio is inside the axle.
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Old 06-15-2014, 06:04 PM   #5
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Saw no sign of a tag, there was some imprinted letters on the diff cover, but none of it was indicative of the gearing.
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Old 06-15-2014, 08:36 PM   #6
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You didn't say what trannys but in 97, 3.07 was the standard gear for both trannys and 3.55 was optional for the 5 speed manual. In 2000, 3.07 was the standard gear for both and 3.73 was optional for the 5 speed. The standard gear with a D44 rear was 3.73 but from what I have read, was only available as a high altitude option behind the 3 speed auto. My guess is, the 97 has 3.55s and the 2000 has 3.07s. My son's 97 has 3.55 and runs much better than my 2000 with 3.07s. 3.07s behind an overdrive tranny will stink with any size tire.
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Old 06-15-2014, 08:47 PM   #7
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Both 5 speeds, so from my small amount of knowledge 97 has an AX15 and my 2000 has NV3550
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Old 06-15-2014, 08:50 PM   #8
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That is true. Don't recall the ratios but I think they are pretty close between the two. Does either have the optional D44 rear? If so, then it should be 3.73 gears if they are still stock.
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Old 06-15-2014, 09:30 PM   #9
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Just did a search for the gear ratio differences between the AX15 and NV3550. BTW, I have to search from google to find it but there is a very informative thread on the Jeep forum. Type in SPECIFICATIONS FOR JEEP WRANGLE TJ and it will guide you to it and has a multitude of information for all the TJ years.

AX15
1st 3.83
2nd 2.33
3rd 1.44
4th 1.00
5th 0.79
Rev 4.22

NV3550
1st 4.01
2nd 2.33
3rd 1.39
4th 1.00
5th 0.78
Rev 3.57

So, it appears 1st and rewind would be the only two gears you would probably notice any difference.
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Old 06-16-2014, 02:45 PM   #10
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Thanks for the info, I didn't even thinking about the trans gearing differences. Any tips for a tune up and/or chasing a VAC leak?
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Old 06-16-2014, 05:34 PM   #11
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I would stick with a conventional type plug and stay away from exotic plugs such as SplitFires, E3s and Bosch. The stock copper core plugs are pretty decent but I have had some bad luck with Champions in the past so I prefer Autolite plugs. The Autolite copper number is 985, AP985 for the single platinum plugs and APP985 for the double platinum. I run the AP985 single platinums in our 97 and 2000 and have had great results.

As far as chasing the vacuum leaks, I would visually inspect all the hoses and connections first. If you suspect you have a leak and are just having a really difficult time finding it, you can use a propane torch unlit and just crack the valve open as you hold it around the various vacuum connections and where your tbody mounts to the intake. Do it in a well ventilated area and just do a small area at the time. If the motor speeds up, you have found a leak.

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