Fuel Filter and MPG
 

So I have access to a performance external fuel filter for basically free (like a $100 value). It filters particles down to 4 microns I think. Could I expect any gains from using this? I'm not sure what the OE specs are, but I would imagine that this filters fuel better.

Because it might filter better? Not a snowball's chance in hades. What has been proven to improve mileage, which deals with the fuel delivery system, is going from 4 hole injectors to 12 hole injectors.

Well I'm sure contaminants in fuel have a negative effect on performance. A better filter will result in less contaminants.

I went from 1 hole injectors to 4 hole injectors in my jeep. The difference was huge! It ran so smoothly after that. I think I got a difference in mpgs. I really want 12 hole injectors though

You've got a 4.0 trying to shove power through an AW4 in order to move a literal brick through the air. There is so much inefficient slop in that chain, do you really think a tweak to fuel delivery is going to be noticeable in mpg once it gets through the engine, an anchormatic transmission, the driveline and tires and the aero losses? You'll notice more of an improvement by rearranging the deck chairs on the Titanic than upgrading an XJ's fuel filter.

If you got an improvement, it was because you had an injector that needed replacing. 1997 model year had OBDII. Get an SG or UG and you can see real numbers.

You sound a lot like those naysayers that say "if you want good mpg, buy a Prius". There's a guy on another forum that got 25 mpg in his Cherokee with an AW4 with a modest parts budget. It is possible to get good gas mileage in a 4.0

None of what you said was helpful. I'm interested in the potential effects contaminants can have on overall performance.

I'm also not upgrading the filter. I'm adding an additional filter. The OE micron rating is 10, and the performance one is 5 or 4.

No harm trying that filter if you ask me. It's not a turn for the worse, that's for sure.
Who knows your car might run a little smoother--->you drive a bit more relaxed-->slightly better fuel economy.

You're not going to get good, as in Prius, mpg, but you can get good XJ mileage. And that's a great thing- EcoModder isn't about buying new cars, it's about maximizing what you have.

The first piece of equipment you should buy is a ScanGauge or an UltraGauge: once it's calibrated you won't have to think you got a difference in mpgs, you'll actually know what you're getting. That's critical, because as iikhod alluded to, your right foot is where the biggest improvements are. But the overall sloppiness of SUV efficiency can't be ignored. You can work on aero and tires to get some impressive % gains in mpg. This thread from a long time ago shows some good aeromods to think about that are very nicely done, without changing the look of the vehicle: Jeep Cherokee Aeromods. As to tires... what psi are you running, and are you taking their diameter into account when calculating your distance traveled?

As it is, any increases in combustion efficiency that an extra (see?, I didn't say upgrade) fuel filter may bring are going to be more than counteracted by your other mods that increase the amount of gas being squirted into the cylinders: the CAI and throttle body. The 4.0 has enough power to move the rig. Throwing extra gas into it isn't very good for increasing your mpg. If "efficiency" means towing a boat up a mountain quickly, then by all means, shove more gas into those cylinders and get as close to perfect combustion as you can. If you want to improve your mpg, find a stock throttle body and while tearing out the CAI, think about designing a warm air intake.

But if you're not going to get a ScanGauge or UltraGauge, at least get a Fuel Shark.

I really like ecomodder--it has helped me a lot. I've toyed with the idea of buying a scangauge for a while now. I suppose that should be the next thing I buy. It is hard to see the difference in some mods with the normal variations in tanks. For example, last tank I got over 17 mpg, but this one it looks like I will get at least 19 mpg (though it is warmer outside). I did see an improvement with the throttle body and CAI, but like you are implying, it is hard to know without the scangauge.

My tires I run at 34 psi. I've seen a lot of people recommending to run them at max psi, but is no one worried about uneven tire wear? Although the max psi on my tires is 60 psi... I'm not sure if I want to have them that high. My tires are getting old though so I will try bumping it up a little. I do take my larger tires into consideration... I need to multiply my miles by 1.04 for an accurate reading.

Hopefully I have a scangauge before I install the fuel filter. Most people here value mods when they are validated with a scangauge.

With a gauge, you don't need to wait for a whole tank. Using the short trip numbers, repeated trips can tell you tons. "Normally at this part of my commute I'm at XX.XX mpg, today I'm up 1.5. What's different?"

A member previously tested tire pressure with coastdown testing. I believe the results, on a metro, had significantly diminishing returns above 45psig.

Ultimately it depends on the carrying capacity of the tires and the weight of the vehicle.