TJ feeler info

[gtmud]

Wife and I bought a 1998 TJ, 3" Blackdiamond lift, tube bumpers, 31x10.5 R15. The down side is its a 2.5 4 cylinder with the auto 3 speed trans. Yes, it IS gutless. I went threw teh engine( new pistons,rings, rod bearings, oil pump, H-gasket, lapped the valves w/ new seals. It runs great, but need a little bit more "out of the hole" power.
I thought these TJ's had 4.10 gears, no tag on the diff's. What would I be looking at to re-gear this and what ratio should I use. This is just DD, no mudding. Really thinking of flipping the jeep for a 4.0 model.

[ex-tbd85hilux]

I have a '97 with a 4 cylinder, an automatic, and JK Rubicon tires (32's). I can run down the interstate with minimal issues I just have to remember it's not the Hemi in my Ram and don't plan on going anywhere quickly. She will maintain interstate speed on everything but the heaviest of inclines (High rise bridge). It's also running 4.10 gears. The prior owner said they were upgraded from 3.73's but I haven't checked to see if the VIN indicates that it did come with 3.73's. I'll be doing that when I get back.

The argument for a 2.5L vs the 4.0 is a long one and is all a matter of opinion. The 4.0 is more powerful and one of the best engines put in a Jeep (IMHO) but that power comes at the cost of weight. The 2.5L is lighter and less powerful. I haven't heard of many major issues with either of those engines overall. I started wheeling with a 95YJ on 33s and a 2.5L and I couldn't use 5th on the interstate. I then moved for a lot of years to an 85 Toyota Pickup with the 22r 4Cyl and the regear did amazing things. But at a cost. It's expensive in most cases. Figure a good quality shop will do the gears for $1000 to $1500 for front and rear. The thing I don't understand is you say your running 31's with 3 inch lift. 31's should fit with stock suspension and shouldn't effect much over the stock 29's the 2.5L came with. You may want to take a look at the engine sensors. How does the 2.5L run? Otherwise here's some cost effective upgrades or checks you can do that might make a little difference.

3 things you can do to wake the engine a little bit.

A 4.0 throttle body is a direct bolt on from certain model cherokee's and most Grand Cherokee's. There is a tab that might need to be ground off prior to installing but it will fit. This will allow the engine to breath better kind of like a big bore throttle body. $25 or $30 for a used one from PNP.

Another power adder is to remove the mechanical fan for an electric. This will reduce the load on the engine by removing unnecessary accessories. They have setups on ebay for ~$150. You could also use a Taurus dual electric fan setup but it takes a little more work to fit it in and if you aren't electrically savvy I wouldn't recommend it.

The last thing is take a look at the exhaust. If it's been modified behind the Catalytic Converter try to get a stock muffler and tail pipe put on or one that's no more than 2 1/4" dia. Most after market exhaust is for 4.0 and use 2 1/2" exhaust which causes scavenging in the cylinders. The 2.5 really needs the back pressure or you lose your middle power band. Headers are ok but you need to make sure the exhaust is not flowing too fast.

One last thing is when were the bands adjusted on the transmission? On the old Automatics that came on Chrysler's they had a forward band and a rear band that needed to be adjusted when ever a fluid/filter change was performed. As they age I think Chrysler actually recommended for a little while a mid-adjust between fluid/filter changes.

Hope this helps and gives some food for thought.

Paul G.

[gtmud]

Thanks Paul, I have been over this engine with the DRBIII scanner and all sensors are reading per spec. Engine runs smooth. We had a 92 YJ w/ the 2.5 auto and really no problems with power. So unless there is a differant set of gears other than 4.10's that might be my issue.
Yes the lift is suited for 33's, but it was on the jeep when I bought it. I am thinking that due to the auto tranny, that maybe where I am loosing my power. I was told it was a new trans, but once its legal I will run it by the tranny shop to have them look it over. I did adjust the TV cable a bit so that the trans won't shift so early, lugging the engine. OUtside of that I am going to install a 4.0 throttle body and machine the intake to accept the larger T-body.
The exhaust has an aftermarket system ( at least a flowmaster muffler) but it looks like it is running the stock tail pipe. The stock air box is stilll installed, was thinking of a BANKS or AIRAID system to replace that.
Also the electric fan idea is a definate, I instaled one on Matts YJ and was impressed with how well it worked(flex-lite).
I am hoping that after spending all the $$ for these things (minus the T-body-free) that some power will be restored. I am still leaning towards just cutting my losses and selling it and purchasing a 4.0. The jeep is in really great shape, just needs a bit more under the hood!
I know what the problem is!! The wife has been driving either our late 05 explore w/4.6, or at times my Bronco-5.0ltr. She is just used to the power of a V-8! NO WaY am I putting her in a CJ w/ an 8 cylinder:).