ZmOz, please explain about your gas mileage.

You just wrote (in the thread about removing roof rack)

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"Well, I know when people put a spare tire up there, they lose 1-2mpg. Even if it was only .3mpg, I would think over 1000 it would be worth it to take them off. I was going to take mine off when I was only getting 11mpg, but thank god I fixed that problem. "
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Assuming it's the same '96 stock XJ you're talking about, how on earth did you jump from 11 mpg. to the 20/25 mpg. you say (recent thread on gas mileage) you're now getting?

Very embarrassing. I just went back & re-read your post on the gas mileage thread & see that you credit the gain to replacing plugs/wires/cap/rotor/fuel filter w/original parts. So what kind of parts did you replace that were cutting your mileage so much?

I just had all that done to my '96. It didn't occur to me to ask the excellent shop that did it what kind of plugs/wires/etc. they were using. Can I assume they'd use OEM parts or should I have specified them?

When starting out you need to baseline the XJ, best way is to use OEM parts, Champion plugs FROM THE DEALER, cap, rotor, wires. The dealer supplied plugs do differ from the ones you buy in a parts store. Once thats done and you get the 'sticker milage' or better you can then start playing around with the aftermarket stuff. The aftermarket stuff generally does not give you any improvment. The manufacturers have pretty well nailed down what works and what does not when they go thru the federal cafe tests. One of the biggest hits on milage is tire pressure, big time, too low and you really suffer, most don't air up with cold weather like they should. If you get the sticker milage and then a few months down the road see a hit in milage it's time to check whats wrong, O2 sensors play a big part in milage, they can run you too rich or too lean, unfortunately there is no simple test for this except to replace it or them, OBDII XJ's, 97 and newer have two for sure, 96 may, not sure about that. My 98's milage goes up and down. It took a big hit about dec or jan which was interesting because ALL our vehicles took the same hit, the jeeps and the oldsmobile as well as some other people that I know. This had nothing to do with 'winter fuel' either, my 98 and the 97 Olds both run very well on the oxygenated winter mix so I blame whatever happend on the gas companies. Personally I think they cut the base fuels with something that was cheaper and does not work as well as whatever they were using.

I just used the cheapest parts I could find, because I planned on selling it soon. I have decided to keep it now. Cheap $1/plug Champions, $12 set of Bosch wires, and the cheapest cap and rotor they had. All these parts had about 200,000 miles on them. After I replaced them, it had absolutely no effect. Then I reset the computer, and BOOM, from 11mpg to 18. Now that it has warmed up I'm getting about 20. Something is seriously weird. I think that's against the laws of physics. That's with usually pretty short trip driving, most often about 10 miles on the highway at ~70. If I drove like my grandma and went the speed limit I would probably get 22+ city.

There are still several things I could be doing to get even BETTER mileage:
Remove roof rack
Use synthetic/thinner oil (using 10w40 dino now)
Convert to electric fan
Upgraded coil
Switch from full size spare to donut spare (or remove it all together and get AAA)
Go on a diet

What year is your Jeep? How did you reset the computer? My '90 XJ is getting about 8-11 mpg . Thanks

Mine's a '96. I reset the computer by leaving the battery disconnected overnight. I believe you can also disconnect it and leave the key on for 30 seconds.

JeepSC said:

What year is your Jeep? How did you reset the computer? My '90 XJ is getting about 8-11 mpg . Thanks

Click to expand...

The '90 is a Renix system. There is no long-term memory. The Renix system resets itself to the defaults every time you turn off the ignition.

Eagle said:

The '90 is a Renix system. There is no long-term memory. The Renix system resets itself to the defaults every time you turn off the ignition.

Click to expand...

So I shouldn't bother trying to reset my computer? I have left the battery unplugged over night, and turned the ignition on a few times. I still had my radio stations saved, so I am assuming it didn't reset.

??

The computer didn't save your radio pre-sets. ODD... aftermarket stereo? Usually once you diconnect for that long you'd lose them...

That was very helpful, Rich. My tire gauge got misplaced in the shuffle of changing cars but I'll buy a new one immediately. A new O2 sensor is going in momentarily. And of all the parts you mention, you seem to emphasize the plugs. Do you think it worthwhile to change out my brand-new plugs, if nothing else, for the dealer ones or just wait for the next tuneup?

ZmOz, this will probably confirm my status as stupid-questionmeister, but let me get this straight. Is there a connection between your replacing those parts w/dealer ones & resetting your computer? That is, would resetting the computer not have helped--or helped so dramatically--if the plugs,wires, etc., had not been the factory components?

I heard on the news today that gas might reach $3 before summer's well underway, so I'm studying your list of other gas-saving options. I refuse to remove my roof rack; it's too handsome on my beautiful red car. I'll go on a diet first. If I move the front crossbar to the back as someone suggested, how many lbs. do I have to lose to compensate for it?

(Of course we could always drill ANWAR )

Churchlady said:

ZmOz, this will probably confirm my status as stupid-questionmeister, but let me get this straight. Is there a connection between your replacing those parts w/dealer ones & resetting your computer? That is, would resetting the computer not have helped--or helped so dramatically--if the plugs,wires, etc., had not been the factory components?

Click to expand...

I didn't use dealer parts. There's no reason to waste your money at the dealer on parts like these...they are exactly the same as you can buy anywhere else in a Mopar box for 3 times as much. I used the cheapest parts I could get at Schucks, because at the time I had planned on selling it soon. Resetting the computer wouldn't have done anything if I wouldn't have changed the plugs, it's just that my old ones were REALLY worn out. They had 195,000 miles on them...they should have been changed at like 60k. :shhh:

In case you're still on, should I try resetting my computer right now after my fresh tuneup, or should I wait til the new cat/O2 sensor are in?

You can try it now if you want...it certainly isn't going to hurt anything.

I've done all this except the computer and am getting 10mpg still.

How does one reset the computer?

ZmOz said:

I just used the cheapest parts I could find, because I planned on selling it soon. I have decided to keep it now. Cheap $1/plug Champions, $12 set of Bosch wires, and the cheapest cap and rotor they had. All these parts had about 200,000 miles on them. After I replaced them, it had absolutely no effect. Then I reset the computer, and BOOM, from 11mpg to 18. Now that it has warmed up I'm getting about 20. Something is seriously weird. I think that's against the laws of physics. That's with usually pretty short trip driving, most often about 10 miles on the highway at ~70. If I drove like my grandma and went the speed limit I would probably get 22+ city.

There are still several things I could be doing to get even BETTER mileage:
Remove roof rack
Use synthetic/thinner oil (using 10w40 dino now)
Convert to electric fan
Upgraded coil
Switch from full size spare to donut spare (or remove it all together and get AAA)
Go on a diet

Click to expand...

You reset the computer on the 91+ models by disconnecting the battery for 5 or 10 minutes. However, that's a shortcut. After 5 complete start-shutdown-restart cycles it will adapt to any new conditions automatically.