Fuel economy

[tbburg]

I noticed the same hunting behavior while I still had the 3.55s. It'll still hunt occasionally on steep hills, but not often any more. (Most recently on the climb out of the valley on 17 north out of Phoenix)
techno1154: I did the 3.73s when I had to rebuild the rear axle, 'Figured what the hell, I had a above-split true-trac on the bench, so the front axle cost was a gear set and master rebuild kit. It actually worked out perfect(speedo is aprox. 2mph off, exactly the same as it was from the factory before I put the larger tires on.)

To everyone with the 30" tires/crappy mileage in 3rd: Can you tell if your torque converter is locking up? I was just wondering about that when I read MoFo's post. The way I shift(manually) is I wait for the trans to drop into 3rd, and accelerate back up to speed, then drop the shifter in 3rd when It's about 1-2mph below the cruise control set point. About 3 seconds later, I'll see about a 4-500RPM drop in engine speed when the TC locks in 3rd.(The TC won't lock in 3rd gear while the shifter is "D", but it should lock up anywhere above 19-2100RPM with the shifter in "3")
An unlocked TC may explain both the mileage and rpm differences we're noting. Also some of the heating up on long climbs.

By the way, I just went out up north last weekend. Spent 45 minutes, maybe as much as an hour in 3rd climbing out of the valley(1500 ft to 6900ft - GPS makes these numbers so easy to get!). For that 155 mile stretch, I got 18.2mpg.(included some of the downhill coming back, about 1000 feet of altitude. The rest of the trip down(about 4-4500 feet drop in 74 miles, I got an amazing 23 mpg! Total combined for the whole trip was 19.2)

 

[CharlesS]

Granted there are variables between vehicles, but the last time the Jeep had 23 mpg was when it was new in 1997.
The best mileage I get in the '98 is 16 mpg with 5.5" lift, 32" MTRs, 4.56s and AX-15 is around 63 mph (2400 rpms).
Two months ago I upgraded the factory original one hole fuel injectors with the new Bosch 4 hole.
The upcoming trip to Moab the end of this month will show any increases in performance and gas mileage the Bosch 4 hole fuel injectors are reported to provide.

 

[srmitchell]

I've complained before about my 265/75/r16 retreads, they weigh 60 lbs each. I think that has a lot to do with my bad mpg.

Mpg at 65mph for me is right around 14-15 mpg. I can see the gauge moving.

 

[techno1154]

To everyone with the 30" tires/crappy mileage in 3rd: Can you tell if your torque converter is locking up? I was just wondering about that when I read MoFo's post. The way I shift(manually) is I wait for the trans to drop into 3rd, and accelerate back up to speed, then drop the shifter in 3rd when It's about 1-2mph below the cruise control set point. About 3 seconds later, I'll see about a 4-500RPM drop in engine speed when the TC locks in 3rd.(The TC won't lock in 3rd gear while the shifter is "D", but it should lock up anywhere above 19-2100RPM with the shifter in "3")

The TC lock up just fine,...or does it? It lock up at about 40 +/- MPH with the lever in 3. In 'D' it lock up at 45 +/- MPH. However,....however I am yet to experiance the high RPM drop that you listed. I see 200 to 300 RPM drop for the years I have driven this XJ. I thought that was normal. Maybe I need to take a good at the AW4. I wonder if that is the reason the RPM always seem to be 100+ above what it should be based on online calculators I have used?

At high way speeds when I shift into 3rd I reduce the RPM to below 3,000 as a way to reduce fuel consumption. Remember, I am almost always using the cruise control which tries to maintain speeds to within 2 MPH or less of the set point. When I am pedalling, it do not matter. The XJ will loose some MPH but will make it up in 4th and OD just fine. Anyway, as already outlined, I regeared to 4.10 to fix the gear hunting. Although I could have lived with it, the old 8 1/4 was howling at me. I had a D44 in the back yard that need some work done so I had it rebuilt to 4.10. Now it seem I have gone a bit too far for my liking,.....nothing a tire size change cannot fix.

 

[MoFo]

Contrary to what I have read here and other places, the AW4 absolutely will lock the torque converter in 3rd gear when the shift selector is in the D position. I am still driving my rig with the bank of LEDs attached to the TCU. I can see the TCU lock the TC at about 35 MPH, shortly after it shifts into third gear, then it stays locked through the shift into fourth.

I would really like to see all the AW4 knowledge here combined together into one FAQ. This information is scattered, sometimes conflicting and difficult to find.

 

[CharlesS]

Years ago a friend of mine had a '98 4.0L, AW-4, NP 242 with 4.10s, 4.5" lift and 33s. He said that on the level highway the torque converter would stay locked, but when there was an increase in grade; the torque converter would periodically unlock and lock. He thought the problem was electrical and took the Jeep to the dealer.... The dealer couldn't find anything electically wrong. The technician said the problem could be that the engine was operating in the wrong RPM range for the torque coverter to stay locked. He decided to get a second opinion and contacted Jeff Sugg at Mechanically Inclined Technicians (MIT) in Santee, CA. Jeff said that the problem was definitely caused by the engine operating at the wrong RPM for the torque converter to stay locked. Several of his customers had the same problem and the solution was lower gearing.
Jeff recommended replacing the 4.10 gears with 4.56s. Once the gears were replaced...; the cycling of the torque converter was gone.