1997 2.5 only getting 8 mpg
- Thread starter Tarpon230
- Start date
8 MPG is pretty awful. What gearing do you have? I would bet your jeep isn't geared properly to handle 33's therefore its struggling to move and burning more fuel.
Yes you should be getting better mileage.
How old is your 02 sensor?
If you don't know, I would spend a few bucks and replace it with a Bosch # 23506 upstream 02 sensor.
02 sensors have a shelf life and become inefficient over time.
Edit: insert NTK, delete Bosch. I know better. I had the right part number, wrong brand.
Please slap me if I do this again
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A thought is that your speedometer is off. there is a small gear on the outside rear end of the transfer case that is easily changed to correct speedometer. you do need to know your gear ratio. This chart can help determine if maybe a previous owner has changed the gear already if the Jeep is new to you. It is a quick and easy job. I have a 2.5 with 31 inch tires and 4.56 gear ratio. I get 15 miles to a gal. max so far on one tank fill up is 286 miles.
Good advice above. Did your mpg suddenly drop to 8 mpg? If so that's the usual sign of the upstream O2 sensor having failed. If it has always been 8 mpg that could be from not having regeared your axles to raise the engine rpms back up to where they need to be for your 33" tires. An engine operating at lower (or higher) rpms than it is most efficient at will have a negative effect on its mpg.
This is the only upstream O2 sensor I'd install... https://www.amazon.com/dp/B000C5O02M/?tag=wranglerorg-20
Make sure not to go with a Bosch if your local auto parts store tries to push that brand on you, Bosch O2 sensors do not work well for long in our Jeeps. Stick with NTK/NGK which is the OE brand.
Make sure not to go with a Bosch if your local auto parts store tries to push that brand on you, Bosch O2 sensors do not work well for long in our Jeeps. Stick with NTK/NGK which is the OE brand.
No the speedometer gear is in the Transfer case. only one is needed. here is a pic. undo the connection by sliding the red keeper up, then you may need to push the side in with your thumb a little where the keeper was. Loosen the bolt for the forked clamp and gently tug the gear out. its quick and simple honestly. oh you may want to order a new O-ring. when I pulled mine out the O-ring was good so I just used the one I had.
oh I don't think I answered your question. using the chart I posted about draw a line from the size of your tires and then intersect with a line of your gear ratio. you come up with a 31 in a green box. order a 31 tooth green gear.
For 33's and the 2.5, 5.13 is what you want. The fours just do not develop much torque so you need the extra rpm's to keep up momentum. For reference, I run 4.88 with 31's with the lower geared 6 spd and slightly more hp/tq 2.4, works awesome.
Read this before choosing gearing. https://wranglertjforum.com/threads/2-5-re-gearing-questions.4804/
I hope the new sensor solves your issue.
I hope the new sensor solves your issue.
Sorry I'm more confused after reading for 2 hours. This is what I have 1997 2.5 automatic 3 speed transmission dana 30 front dana m35 in the rear 3.73 rear axle ratio 33in tires. I ordered a new upstream o2 sensor will be here tomorrow, Also ordered the correct speedometer 31 should be here on Friday. Daily driver not much off road, live in Florida no real hills, not much highway driving. Mostly around town. Its a dog off the start and my gas mileage is 8 mpg, if I regear will this help?
The 3 spd auto changes things, and not in a good way. 4.10 would help some, 4.56 is too deep. 4.30 would be great, if they were available.
Definitely run through the recommended fixes first and see if they help; full tune up, o2 sensor/s, correct speedo gear.
Definitely run through the recommended fixes first and see if they help; full tune up, o2 sensor/s, correct speedo gear.
Yea something is off. 8 mpg if your rocking a Bronco or blazer is about right. That’s way below a “my jeep gets bad mpg”