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!

I forget sometimes and go in the store for half an hour to get things I forgot to get. lol Come back out and there is a gallon and a half on the ground.

I can't do humid man... I can do hot, but not humid.

1999 xj 4.0-while driving in Vermont (50 mph speed limit) I get 24 mpg.
Driving in NY (usually about 65 mph) get 18- 20 mpg.
Using remote starter in the winter to warm for wife, I get about around 12 mpg if lucky.
Compute mileage every fill up. Unexplained drops mean a problem, such as air filter, plugs,brake dragging, and such.
Every Mopar vehicle fuel gauge i have had had a large bottom 1/4 tank. 59 VW truck had none. just a lever (reserve) to get you home.

So I took apart the dash today to begin wiring switches.... and the fuel guage died. The needle no longer moves while my speedo is still working.
https://cimg7.ibsrv.net/gimg/www.che...4be8cd025c.jpg
I have the basic guage cluster for 1996 with the manual trans shift light on the left set of indicators. Does anyone know if I am able to just directly swap to the upgraded set of gauges or do I need to replace with an identical one to what I have? Also if anybody has a spare fuel gauge lying around I'd happily pay for it

https://www.cherokeeforum.com/f2/gauge-swap-question-240484/?highlight=gauge+swap

I did the gauge swap upgrade and love it.

I also still have my old gauge cluster and the fuel gauge worked fine if you want it.

What do you mean by the sending unit? The fuel pump? A part number or reference number would help. Lord knows mine is 22 years old so it's probably time to change it anyways

Yes... the fuel pump assembly. It has the float and sensor incorporated into it as well. Give me a few... I have to go take care of something important and then I will try and find a picture to explain more about what happens. :)

There are three things can contribute to a problem like you are having. First if you know for sure this is the original then you can rule this one out. If it has been replaced at any point it is very easy to bend the float lever during installation and throw off how it will read the level. Tact and caution is very important when snaking a new assembly into the tank to make sure this doesn't happen.

Here is the old fuel pump housing from my 97 showing how the sensor/float assembly is mounted on the side. Yours should be similar I would think.

https://cimg2.ibsrv.net/gimg/www.che...b86974e54e.jpg

Next the sensor works with a "finger" riding up and down an arc of contacts on a board. You can see here where it is shiny from the finger riding on the contacts. These contacts are embedded into the plastic board but are not as thick as they should be. So what happens is after awhile they can wear through and mess with how it is reading the level.

https://cimg3.ibsrv.net/gimg/www.che...921fa3c505.jpg

And the third issue that can come up is the float it's self. The float is made of plastic and over time becomes very porous. It will get so porous that it soaks up fuel, gets heavy,and no longer tries to float correctly anymore and becomes a problem with reading the fuel level.

https://cimg4.ibsrv.net/gimg/www.che...9349849717.jpg

Now as far as brand and part number I would not be able to tell you from experience what would be best. I had to get what I could get for mine from O Reilly's because it was the only option I had at the time and don't remember what brand it was. Maybe someone with more experience with the fuel pumps on these can jump in with some suggestions?

Edit: In looking at these close again I noticed that the middle connection on the left of the contact arc has some scratches on it. These should not be there. This means the finger was riding on that and probably losing contact with the arc board contacts. This would make it short to that instead of touching the board and read that particular level until it cleared above or below that spot.

The 96 should use the old style pump mounted facing the vehicle front in the tank. Most of the replacement units typically sold for the 94-96 model year are JUST the fuel pump itself and do NOT include the sending unit.

Interestingly enough, it seems that the Mopar pump DOES include the sending unit assembly, for the low low price of $300 (compared to the pump by itself for ~$75).

On a positive note, it appears that you don't have to drop the whole fuel tank just to swap the pump assembly. :)

https://www.moparpartsoverstock.com/...5102118AB.html

Shop around local to see what they have, but the whole assembly is what you want. They run about 250 or less. here is a Crown to fit yours just for reference.

https://www.partsgeek.com/catalog/19...fuel_pump.html

This is what I had to pay for my 97 pump. It is what it is. :)

Interesting, I get 18-19 highway but, only 9 MPG around town.

I was talking with someone at lunch about O2 sensors and considering replacing mine. Only have about 65K on the Jeep though. My friend said the sensor should be replaced every 50K. Is that true?

Okay so now more weird stuff is happening. I went to leave work today with my fuel gauge still dead. I got about a mile and a half down the road and she sputtered out and died. My coworker stops and took me to go get gas and I put about a gallon into the tank enough to get it started. I get it to the gas station and she only took 17 gallons which means at least two gallons were in there before I put fuel in it. I think I'm just going to change everything, the fuel pump the fuel gauge and anything else that looks like its original equipment because at this point it's all 22 years old and probably dry rotted

The only other possibility I can come up with right now is that because today we are experiencing very high winds, 30 mile an hour plus then potentially because I was already low on fuel excessive amount of air being taken in caused the fuel-air ratio to get off enough for it to sputter out kill the engine, but I find that highly unlikely.

I was able to fuel up at the gas station and drive home though so I doubt it's the fuel pump

It wouldn't hurt to check the pressure anyway to confirm it's steadily holding pressure.
It might behoove you to get under it and inspect the connectors and hoses and all of that so you know if they're in bad shape.
Wire sheathing (if that's the right term for it) can dry and crack as well.

So then what's the difference between the old style sending unit and all these aftermarket electric pumps that are being advertised on the page just below it?

The sending unit/sensors are basically made the same and work the same way. The difference he is talking about is the orientation of how the whole assembly mounts into the tank. My 97 is mounted in through the top as where yours is mounted in through the front of the tank.

At first you were posting about your gauge not working correctly, now you are having additional issues with the pump. It sounds like you might have a bad ground causing both issues. Or the fuel pump is now getting ready to go out on top of the sensor not reading right.

Mine started to just occasionally do what yours just did once in awhile. And it was still working when I changed it out. But since changing it out it has not sputtered again, so I know for sure it was the pump failing intermittently and only now and then on it's way to quit completely.

And it would be a mistake to not change out the whole assembly rather than just the pump.

Yep, sorry about that.

The good news is that on a 96 you do NOT have to drop the entire gas tank to get at the pump - on a 97+ you DO have to drop the whole tank. So be happy that IF it's a bad pump (and not grounds/wiring - Did you clean and tighten the ones behind the driver's side trunk panel yet?) then you have the more convenient setup for replacement.

Especially if you have a 97 and newer with a SKID PLATE and class 3 HITCH! lol

It took me most of a day to get that all lined back up again and get all the bolts started. It wasn't bent when I took it off, but it was all bent when I put it back. How does this happen? lol

Oh jeez, I can only imagine the PITA it is with the hitch.

I dropped the tank 2x on my 00 TJ, the first time was because the skid plate (the tank actually straps right into the skid plate on it) rusted out and the second was to replace the fuel pump. Getting it off was straightforward enough, but I remember the pain it was getting it back up. I had the tank on the floor jack and had a helper maneuver it while I was under the jeep looking up at the mounting studs. I don't remember anything being bent, but a lot of the stuff was new.
It is no joke when they say that you want as little fuel in that tank as possible.
I guess it wasn't as bad as I had feared, but I had a long standing notion from when I was a teenager and knew nothing about automotive components that "dropping the gas tank" was a huge effort.

Mine came apart fine also. But somehow while they were sitting there waiting to be put back on they got bent. lol

I'm sure they were probably already bent but while bolted on they were being held in proper shape until I took them off.

So when I started putting it all back nothing would line up at all. At one point I thought I was going to have to bend all three, the hitch, the plate, and the CAR to make it all fit again!

If it happens again I'm cutting a hole through the rear deck floor instead of pulling all that apart again. lol