1999 XJ with 4.0 and AW4 137,000 miles The old trans has been abused by a high schooler PO. When I got it, I had to clean the trans because there was brown crud everywhere (replaced filter twice and did drain/refill 5 times in one year.) It would rev up to 3,000-3,200 rpms to up shift from first to second, then 2,800 rpms to go into third. And it would finally go in overdrive at 65 mph. So when I got my Xmas bonus, I went to a salvage yard and they had a 2000 AW4 that was at 98k miles and they certified it as in excellent condition. So I picked it up and I replaced front and rear seals, new filter. And recently, I swapped that into my jeep. It shifts great, I ll tell ya. It goes through all gears just under 2k rpms. So now I'm puzzled why my gas mileage is much worse than the old transmission? It doesn't make any sense. Am I supposed to flash the ECU by touching positive and negative battery cables together? Any other suggestions?

Is it not related to the trans and the problem lies somewhere else in my jeep?

 

Is the replacement transmission going into Overdrive?

 

I would like to add that I did adjust the TV cable. Even adjusted it and moved a notch forward, and then back one notch. Nothing helps

 

Yes ii can see it up shift three times, and I was able to breeze down the highway 70 mph at 1,500-1,800 rpms

 

Was I supposed to get the TCM from a 2000 and use that?

 

The 1999 and 2000 XJ TCM's are the same part number.

Did you disturb the oxygen sensors at all when replacing the trans?

 

At 70mph I am at 2250 Rpms. Yours are low for 70mph.

 

New sensors around a year ago

 

Really. That's strange. My gf's 98 xj. Goes 1,800 rpms at 70 mph also

 

Oversized tires could do that. What exactly is your mpg?

 

Old trans got me 13-14 mpg on 235/75/15

New trans is getting me 11 on same tires

 

i would add that I got Bosch oxygen sensors.. Should I have gotten ngk ones?

 

Could the oxygen sensors be damaged when I took out the exhaust?

 

You may want to check the oxygen sensor installations for security, cleanliness, and damage.

I hope the Bosch sensors were exact fit and not universal ones that require splicing.

NTK sensors are the best as far as I'm concerned. They're factory equipment anyway. The Bosch sensors vent to atmosphere through passageways where the wires enter the body and the NTK's vent to atmosphere through vent holes in the side of the body. If these vent holes get plugged up it will affect the voltage outputs to the PCM, which could affect rich/lean trim. It seems to me that the Bosch wire vents would get plugged up easier than the NTK body vents.

That's a pretty healthy drop in MPG I'd say. Humm..

 

It was exact fit. Do u have part number for ngk sensors, both upstream and downstream? I could order after verifying the condition of the sensors.


When I took out the exhaust tubing, I left the sensors on the tube and unplugged it, and pulled out of the way. I ll also check the vent holes too.