tjwalker

Many times there are a COMBINATION of root causes. Especially with issues like MPG.

Winter blend/ethanol could be one part of the total equation, it has relevance and it should be part of the discussion.

This is a forum, not your thread. The OP is more than capable of picking and choosing what he thinks is relevant to his particular issue, don't try to be a gatekeeper.

Guntar13

I am the gatekeeper; are you the keymaster?

HAHAHA sorry i had too. Inall honestly i totally agree with your, there is a combination of things going on. It runs too good to be dumping fuel like that. The plugs look good not gas soaked or anything, just pulled a few last night to check. I am starting to wonder about a dragging brake somewhere or a bad ujoint, basically something that is causing rolling resistance and hurting the mileage.

The Rooster

A dragging brake would definitely do that but any brake covered wheels usually you notice a dragging brake.... Interesting I'm puzzled on this one...

Cherockee

I'm probably not going to be able to contribute much, but may I suggest a couple things.
First, are there any signs that the Jeep as been altered in any way? I once found a "chip" plugged in line with the computer harnesses- something like this could cause poor mileage without effecting drivability.
Next, how about tire pressure? Maybe try overfilling a little, but not so much as to cause poor tire wear.
Does you normal commute consist of a lot of hills? The 4 miles between my parents house and mine will cause me to lose about 5mpg if I have to drive there everyday, where in weeks where I don't go there at all my mileage is much better. Hills can be a big factor.
You mentioned "drag" so it might be a good idea to check that front suspension. Bearing wear and such can cause undue stress on the drivetrian... usually you get noises with something like this but still worth checking out.
Are you hauling lot of needless stuff in the back? Weight can affect mileage too.

Guntar13

No hills and the only extra weight is an ice scraper in the back! I've felt around the brakes after driving a while and no excess heat around the wheels or brakes which typically means that a brake is stuck. Still worth jacking up and pulling the wheels off. Need to poke around a few things this weekend.

Cherockee

Did you happen to check that the resistance reading from the throttle position sensor is smooth, no bumps or anything ?

Oh, and here's one I didn't see anyone suggest- you don't think you're being robbed do ya?

Guntar13

The dog would know if I was being robbed! I was under the impression that on those style jeeps the tps would throw a cel when there was a fault? To that extent I did have my scanner on it and its reads throttle percentage on the fly. Went smoothly up as I pressed the to pedal.

BlueRidgeMark

I'm not trying to be a gatekeeper, I'm trying to clear the chaff and red herrings out of the discussion so that the real cause can be found.

Ethanol isn't the problem, but it gets thrown in every time somebody complains about getting ridiculously low mileage. It's slightly more relevant than the motor mounts. It belongs about at the end of the line as far as things to look at when somebody is complaining about 11 MPG in a vehicle that should routinely do 17-18 or better. It should be considered AFTER more serious problems are eliminated. Instead it gets tossed into every such discussion as though it's the be all and end all. All that does is to distract the OP from looking for the real cause, and reinforces a wrong idea in the minds of the many young kids reading these threads who really don't understand the issues.

BlueRidgeMark

Yeah, normally no heat would mean no problem, but with a mystery like this, it makes sense to dig in and double check. Still, if something is dragging, that heat has to go somewhere. That's basic physics.

Have you checked the diff for heat?


Also, what about your calculation method? Are you taking mileage from an accurate odometer reading and actual fuel usage from what's pumped?

Or are you going by miles per tank?

How often do you calculate mileage?

BlueRidgeMark

I was thinking about this on my way home, crawling along in traffic and listening to my transmission's lazy shift....



Torque converter? If it's not locking up well, maybe that's why your mileage is so bad.

I also have to wonder if it's partly related to your extremely short commute.

Do you see any difference on long hauls?

Guntar13

I suppose it could be a possibility, but I'm doubting it. I've tested it in all the normal ways and works like it should. Not to mention while driving and having the scanner hooked up I can see when it locks up and when it doesn't.

BimmerJeeper

3.6% of 17mpg = .6mpg, so Mark is right, it's not the gas causing 11mpg, and it's not even worth mentioning.

Turbo X_J

Short trips with lots of on-off thats why it sucks fuel. Fill it up and get on an interstate set the cruise at 60 for 1 hour, fill it up again, then report back.

Guntar13

I see your point and while it is still valid I have to disagree some. The 98 we have is used just as much and is getting average 15, and it sees way less highway use then the 99. The 89 I had gets driven the same as the 99 and was averaging 16-17. Something is more puzzling here?

Turbo X_J

Have you verified the odometer/speedo with a GPS? I think it's still apples to oranges tho, most mpg threads are a solution searching for a problem. If it's not dumping fuel and the neighbor kids not siphoning it off, it is what it is.