Strange fuel consumption
 

Hey guys I have a question about how my Cherokee is consuming fuel. When I first started driving it about 12 years ago everything was normal. It would Swig fuel in 4-wheel drive but was generally pretty economic in 2 wheel drive. It is a 4.0 liter with the ax15 and 3.07 gearing and a short ram intake. It's now at 193000 miles and I have noticed for probably the last twenty thousand miles that it wi'll just absolutely suck fuel like a V8 until it's down to a quarter tank... But then I can drive on a quarter tank for a whole week. I do regular tune-ups and change the plugs and wires. It's ran consistently on 87 octane for the last 21 years. It does have a slight lift now and I'm on 29 inch tires versus stock it had 27. Any input you can give me helps. I have ruled out it just being the gauges as the gauge does reflect the actual amount of fuel in the tank. Any help with this problem would be great. I don't want to have to trade it or sell it I'd rather keep it going so that my son can learn to drive on it in 16 more years

Might not be the gauge but it could be the sending unit in the tank. The contacts wear through and it will do crazy stuff like that.

How much fuel are you putting in, and how many miles did you run on that quantity of fuel. That is what you need to determine to really know your fuel mileage.

I always watch my fuel mileage like a hawk. Always have. Can be an indicator for if something starts to go off.

I would say with Tbone.... don't just pay attention to the gauge itself. Record/track your mileage and calculate what your MPG is averaging over the next few tanks, and see if that is staying consistent. If that's not fluctuating much with the same type of driving/conditions, then may help to point towards the gauge/sending unit as mentioned in the thread.

I'm not sure how to help in a thread about fuel economy when the OP doesn't post the calculated MPG. I can add this, the lift and bigger tires hurt your MPGs.

I'm averaging about 16 now.

That's normal. That's what mine is with 2" lift, 30" tires and AW4 w/3.55 gearing. What was your stock MPG? Mine's always been around 16 average, 18-20 highway.

I'm like RocketMouse and track MPG for every tank, and always have.

http://badges.fuelly.com/images/sig-us/33283.png

Wouldn't the real question be how many miles he's getting on a tank full despite how the gauge is reading during that tank full from full to empty?

If he's concerned about tank capacity or operation of his fuel gauge yes, but not if he's concerned about fuel consumption. You don't have to empty a tank to calculate consumption. It does sound like the gauge or sender is the problem though, not the consumption.

EDIT: Or, maybe I don't fully understand your question, Bugout?

I think so too, how the gauge is acting might be confusing him about at what rate it "appears" to be consuming it. :)

I've had gauges do that to me before. I think I'm getting GREAT mileage and then all of a sudden I look down and it went from 3/4 to empty! lol From what I gather in his OP his is doing the exact opposite?

Yeah, that's what it sounds like.

Like you, most of the gauges I've had that didn't work quite right would go about 100 miles until it came off full, then would nosedive from about 3/4 tank to E. In fact, just about every Ford I've owned has had a gauge that acted that way except my old Bronco.

I've noticed that too! I think a lot has to do with how the tank is shaped. Odd shapes create different consumption rate/surface levels as they are emptied. Smaller to larger cavity or larger to smaller cavity at the surface level. It took me awhile to realize this had a lot to do with it. The old bug tanks were real bad about it because of their shape. You know about the "reserve" on Bug tanks right? lol

Yeah, I've heard of the "reserve". My gauges always act a bit like that because I put as much fuel in the neck as I possibly can as well. Can't stand to leave the station without squeezing that last ounce in there! lol

I do that too. lol But in the summer out here you have to be careful doing that. Unless you are getting right on the highway and start consuming it you can't top them off like that when it's extremely hot outside. And I know you know why. :)

The bugs were funny though. Some had a reserve pocket but no tap or valve. Remember those two guys you saw jumping up and down on the front bumper of a Bug or getting under the side and rocking it as hard as they could? They just ran out and you have to do this to "slosh" the fuel out of the reserve pocket into the main part of the tank.

"What the heck are they doing to that?" lol

LOL, yeah it seems I do recall scenes like that back in the day. Hadn't thought about the heat expansion... We don't have heat quite like that here, but oh my lawd the humidity! I'll take that heat and humidity over this 0-20 degree crap as of late though!