Hello, I just had this problem happen the other day. I noticed that at 45 mph my '92 Wrangler (6 cyl..150k mls) started vibrating pretty bad. Then this morning I noticed that my fuel gage was going down pretty quick. I used a 1/2 tank of gas to go 18 miles!!! Still vibrating!! <img src="/forums/images/graemlins/scared.gif" alt="" />. So I changed rotor and distributor cap in case I was misfiring. No help. Any clues??? Thanks in advance.
oh yeah, theres no smell of gas or a sign of leaking and its only noticeable when I'm at 40mph (the gas needle moving, that is )

First thing to do is to seperate the gas guage problem from the vibration problem..
For the vibration I would get to speed and put it in neutral to see if the vibs lessened..
I would go fast to see if they stopped..
I would apply the brakes slightly to see if they stopped..
Vibs at certain speeds can lead to out of round tires or bad tire balance.
Is the vibration in the engine itself? Running the engine up slowly while parked should tell this..
Is the vibration in front or rear? The steering wheel shaking usually means the front..Not shalking usually means the rear..
For the guage I'd fill the tank when 1/2 was showing to see if it truly WAS 1/2 tank..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thanks Big Jim. This is a tough one. Parked and reving the engine up..it goes smooth as normal. At 45ish under throttle I feel the vibration the most, then if I switch to neutral I think less vibration but its hard to tell because I'm slowing down. No steering wheel vibes. Could it be water in the tranny?? I went thru an boot high puddle(sorry, I just remembered that). And the tank was filled up Friday. ?? I notice the tank going down when I hear the rumble of the vibration, again under throttle. If I drive slow the needle stays where it is.

Has your actual fuel mileage changed? Not the rate the needle falls, but the actually miles you are getting per gallon?

For the vibration, if its hard to tell while driving, another thought, is to put the rig up on 4 jack stands so all 4 wheels are off the ground, start the jeep, put it in drive and let it idle, while watching everything spin, and look for anything that looks out of balance.

Sean

Ok then speed up to 55/60 and put it in neutral and see if the vibration comes in at 45 or if it doesn't..
Is it possible that you have an engine miss and are mistaking it for a vibration?
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

This is a shot in the dark, Is it possible that the vibration possibly from a bad U-Joint shakes enough to vibrate the sender for the tank maybe shakeing somthing loose?
If you feel the shake in the seat of your pants it's in the rear if you feel it in the wheel it's in the front.
I would start with dropping the drive shaft and check the u-joint's then the endplay in the pinion(move yoke in and out} yoke should not move. If all that looks good swap rear and front tires see if problem moves.If it does it's in your tires.

If you truly have a fuel problem check your plugs they will tell the story. If it's a carburated vehicle check the fuelpump sometimes they pump fuel into the crank case when they go bad. That is if it's a Mechanical pump mounted on the engine.
Thats all the basic stuff I can think of.

Good luck!

Thanks everyone that answered. This morning as I drove, the vibration got worse and since I need the car for work I couldnt wait to try fixing it myself on the weekend. I figured I'd get stuck somewhere. So I brought it to a mechanic. It was the U joints, which ones - I forgot to ask. Good guess Toolmakerprevo! As for the gas problem, they didnt see anything obvious but recommended a tune up. that I'll wait till the weekend to do. Even though its supposed to be snowy here. So now I'm at a little more than 1/4 tank. I dont know anything about fuel injection but I'll do plugs, and fuel filter and aircleaner..I already did cap and rotor. Thanks for trying to help me out.

Your welcome I get lucky once in a while!
I can't imagine where all that gas has gone your sure it's not the sending unit.

Ok one down and one to go.. Trex! If it is running good LEAVE IT ALONE!! Your gauge is lieing to you!! You are NOT BURNING the gasoline you think you are.. Your engine won't run as rich as the gauge is telling you!!
You don't need a tune up.. You need to run awhile and fillup at various stages of the gauge to see just how much gasoline is in the tank at 1/4, 1/2, and 3/4 readings..
You have a sender, gauge or wiring problem...possibly..
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

Thats what I'll do. I'll fill up tomorrow, and write down how many gallons it took. A work in progress. I'll keep ya posted.