Sluggish Highway performance... (Not a BS gear thread)

[american_zero]

Your tires are obviously not helping, but have you looked at all your maintenance items? I would check all of that stuff and see if you can make any improvements there first.

 

[srmitchell]

Ive done everything.
New -
Belt
Air Filter
Clean TB
New oil
Spark plugs.

Nothing has been neglected. I even messed with the kickdown cable today, and didnt see much difference.

 

[sunburned]

Rolling mass will make a huge difference in how the Jeep feels. I remember on my Mustang going from stock wheels to bigger, wider saleen wheels, the weight was very noticable when accelerating. Taking even 10 lbs off each corner will be a big improvement, especially because all the weight will be from the outside of the mass since you already have aluminum wheels. I bet going to an aluminum pro-comp wheel or something like that will be even better, but I'm not sure what Moabs weigh.

 

[srmitchell]

Moabs are about 24 pounds.

 

[anthrax323]

I find that on my 4.0 (2001 as well), engine speeds of 2600 RPM and up are fantastic on the highway. I also have a bit of a weak/dead spot between ~2000 and ~2500 RPM - once I get past 2500, passing power improves tremendously.

Bear in mind I'm on 31's with 3.55's, and this behavior is noted in D (3rd). You might just be ever-so-slightly under-geared.

 

[jeeperjohn]

I think you should run a compression check and see if your motor is getting worn out. You shouldn't be sluggish with that gearing and tire size.

 

[collkid]

Well, my Treadwrights don't seem to be heavy compared to a normal tire. That seems odd.

 

[srmitchell]

I think you should run a compression check and see if your motor is getting worn out. You shouldn't be sluggish with that gearing and tire size.

That's a great idea. I have reason to believe it's fine, this motor was never neglected in the 124k miles before me. I have a stack of service records.

I'm driving down to the bay today, and I'll report the power and mpg results.

 

[cal]

Would I be better off reving at 2300 at 65, or 2500 at 65?
Same tire, Maxxis Bighorn.

Higher RPM's will always be better. We have a local who ran 4.56 gears with p235/75/15's for most of last year, ran great and got pretty good gas mileage (17?). I have a stroker, 5.13's and 37's - he would outrun me on the freeway. 4.0 looves to spin up to 3000+ and stay there.

 

[srmitchell]

Mine averaged 17 on the trip down to the bay area. However passing power was horrible, and mileage significantly dropped off given any uphill.
I took a cruise from San Jose to Dublin, and back to San Mateo today, mileage was probably 14. I can't afford to drive this thing anymore, And it's not like I did not know that mpgs would go down given bigger tires, but I search a lot on here, and compared to others, somethings wrong.

 

[jeeperjohn]

Mine averaged 17 on the trip down to the bay area. However passing power was horrible, and mileage significantly dropped off given any uphill.
I took a cruise from San Jose to Dublin, and back to San Mateo today, mileage was probably 14. I can't afford to drive this thing anymore, And it's not like I did not know that mpgs would go down given bigger tires, but I search a lot on here, and compared to others, somethings wrong.

Check for a plugged cat, dirty injectors, bad sensors, vaccum leaks.

 

[american_zero]

Mine averaged 17 on the trip down to the bay area. However passing power was horrible, and mileage significantly dropped off given any uphill.
I took a cruise from San Jose to Dublin, and back to San Mateo today, mileage was probably 14. I can't afford to drive this thing anymore, And it's not like I did not know that mpgs would go down given bigger tires, but I search a lot on here, and compared to others, somethings wrong.

My last XJ was a stripped down '94 sport, 5spd, 4x4 and that would get 17-19 regularly. Saw 21-ish on all highway on a couple of trips. Could still get 17+ with a rackrack on.

My current '93 Country, loaded, A/T gets 15-16 regularly (sometimes 14) highway or not. This was stock with the same tires (30") that my '94 had. It has 65k miles on it and runs great, but the mileage leaves something to be desired. Now its lifted 2.5" or so with 31" tires and I haven't noticed a change in MPG's. Maintenance is all fresh except the O2 sensor which I have ready to be installed. I calculate mileage at every fillup and adjust mileage for the larger than stock tires based on GPS readings.

Just throwing this out there for comparison sake. Oh...stock gearing on both. Leaves a lot to be desired in terms of performance with 30 and 31" tires.

 

[srmitchell]

It seemed to do a lot better when I drove back up. I ran a full can of seafoam through it, and it used less than a tank coming up. I would be fine with 16-18 mpg if I had 33's, but I'm only running 32's, so the mpg isnt worth how small the tires are.

My main gripe is that its just not fun to drive between 50-65 mph. It really starts to pull fast past 67 mph, but mpgs drop off considerably.

Thanks for the input _zero.

The guy who has been helping me with a lot of stuff lately has a lot of tires laying around his shop, so I asked him to find me a set of cheap 265/75's with highway tread, so I can at least run those until I get my new maxxis tires in summer.

 

[blondejoncherokee]

how is the TPS? test it for dead spots? good input output voltage?
how new are the 4 - 02 sensors? good time to replace them if you havet in a while.
any exhaust leaks? have you verified? coolant temp sensor and all that other stuff...
cps ? cts ?
have you adjusted the throttle valve cable? does a 01 have an adjustable TV cable?

14 isnt great but its not terrible for going uphill.

17mpg is not bad at all.
i get around 14mpg when im lucky with 4.88s and 35s.
of course you will loose MPG going uphill with a lifted jeep so im not surprised there.

 

[srmitchell]

I dont know how to test the tps.

All other sensors are clean, the upsteam 02 sensor are new.

Throttle cable is adjusted.

Im really wishing it was a 5 speed. Automatics are FAIL.