also the fuel mix is different in winter.

 

Thats what I just said...
Denser air=More fuel. EX: the trucks this summer. Fuel map established in Iowa where they spend all their time (denser air), go to Colorado/Montana/etc and they start to smoke... Less oxygen in the air, but same amount of fuel as Iowa=diesel smoke...

But my point was that winter fuel makes a difference. I Lost 2.5mpg just from the switch to winter fuel.

 

This guys got the idea minus spark plugs! Run the champion oem coppers, nothing else is needed and your burning money if you get anything else! I personally run Delo or Rotella deseil oil in my xj because it has aditives that will litterally clean any gunk out of your motor, so no sludge builds up! I suggest you run it as well cause you want your motor clean & sludge will kill mpg. Either wayt hats your choice! Rotella 5w40 seems to find its way into my motor though.
My 88 get 18mph average in town only, my jeep hasn't touched a freeway since I bought it lol..thats a 5speed ax-15, 307's 31's and a 3' lift..I do alot of urban/city driving, alot of stop and go..stoplights usually every mile or so.
I've redid every single thing though..motors well over 300k, trans/transfer are less than 2k old. Every sensor, from the temp-02 sensor is new..only sensor I didn't replace was the knocksensor. I have 703 injectors, wrapped header, intake head sheild, and HF cat with a magnaflow muffler, 60mm throttle body witha spacer. All that needed replacing anyway, so I upgraded! Spacer does nothing at all for my jeep, no gains but it came with my throttle body so on it went..before I get flammed for that lol.

My advice is do your maintenance and cheack your tires & get an alignment! You can even add a few extra psi to em which could help. Clean your throttle body & IAV? sensor on throttle body, intake tube & airbox out. I've heard some say adjusting the TPS helps..but I've never done it.
Relocate the IAT sensor, its on the firewall side of the intake manifold, around the 4th intake runer I think..it reads air intake temps and obivously the intake is being heated by the header, which equals false air temp readings. Relocate it to your airbox..it requires extending 2 wires...super easy
Check for vaccum leaks & exhaust leaks! Those will kill your mileage. When you seafoam your jeep if you see smoke coming from anywhere else other than the tailpipe then you've got an exhaust leak and it should be fixed!
Change your air filter if its bad..those cheapy 5 buck ones work great! Change your fuel filter..Mine was stamped AMC which means it could be 23 years old unless it was a replacement..sure looks 23 years old lol.
Once your've done all your maintenance stuff, seafoam it & reset the ECU, drive normal for a week or 2 and that should help. Higher grade gas will do nothing for ya..stick to 85/87. Winter will always result in worse mileage. Cleaning the grounds can help, and can be done with a small wire brush and a few minutes of time, or do what I did and ordr a grounding kit from KWIP..great guy, great product! Like I said if you can upgrade while changing stuff out, do it!

I think theres a few things that will help get better mileage than stock though..like me for example..18.4mpg average, hand calculated and GPS tells me the mileage so thats 100% accurate. And I'm lifted 3" and 31's, and I get on the skinny pedal quiet a bit. 703 injectors & intake heat sheild helped the most in my case.
EPA states a 88 jeep xj with a 5speed should get 16/22 or 18 combined..I'm getting 18mpg in town only and I romp on it alot lol. When I was babying it I got 19-20 but I'd rather get on the skinny pedal a little more vs the extra 1-2mpg..more fun. Once I regear to 3.55's vs my 3.07's I'm sure it'll get even better in town and thats where 90% of my driving is.
If my jeep had no lift & 215/75/5 tires like I stock I'm sure I could get 20mph average in town..just a matter of how you drive.

Follow Dino's Mod diary if you wanna do what I did. He did his research with actual physical results, the rest is common sense and physics..
http://www.jeep4.0performance.4mg.com/diary.html

All of that stuff is super cheap to do, the intake heat sheild is probably where you'll see the biggest gain, cause your intake manifold won't get cooked anymore and it cost like 13 bucks and 15 minutes! I didn't wrap my air box or intake pipe but I'm sure you'd see gains there as well...
Colder/smoother flowing air = more efficiency which = better mpg..colder air will net you more mpgs..I know someone said opposite but its simple physics. Colder air is denser which means you need less air to operate at the same rpm than hot air, so inturn you'd need less gas to burn the air. You won't be using more gas unless your flooring it!
Everything on that page will give you more power so to speak, but it will also make your jeep more efficient, and efficiency = better mpg! I speak from expeirence
I can out run my buddies 96 HO, he has a NV3550 manual trans 3.07's, 4.5" lift & 33x10.5, 99+ intake, 62mm thorttle body, dynomax or thorly header, 2.5" downpipe with a OEM replacement cat and no exhaust, hes 2wd with no interior other than the front seats & dash lol..He also has a stage 2 centerforce clutch..I love his clutch setup.
I have a 88 low output with a ax-15, 3.07's, 3" lift & 31's, 60mm tb, 703's, 2.5" catback/stock bent & crushed downpipe and I'm 4wd with a doluck replacement clutch..I have a full interior and carry another 40-50lbs or so in tools/extras. From the factory he has a more efficient/powerful motor, hes got weight on his side I think but we never weighted them..I have a very slight advantage in gearing..but I shouldn't be able to beat him but I can outrun from a dig or a roll..its close but I can win 9x out of 10. I don't think its the driver has 9x out of 10 he can tree me lol.

If you want to take it even further, then hyper mileage! Slow starts, keep rpms around 2300-2500rpm..yes keep your rpms up. Jeeps don't make power under 2000 so you need more throttle to keep it going..while at 2500rpm you'll need less throttle which = less gas used. Works great for anyone who does it!
Anyway slow starts, stay in the power band, travel no faster than 65-68mph on freeways or posted limit in town, draft when safely possible, and if you see your light turn red, get off the gas & coast..you'll use less gas, and maybe it'll turn green before you get there so you won't have to stop and start again which = less gas used! Stop a little sooner..means get off the gas a little sooner at stop lights or stop signs...Coast as far as possible but don't over do it, people might get mad
Relocated your roof rails as far back as possible, helps with airflow but you wouldn't even notice the difference..but again every little bit helps, it adds up! You can make a grill gaurd/block..most people use a peice of carboard and block part of the grille off..it will block air from enter the engine bay which is like a big net lol and inturn you get better mpg..yes this can have bad consequence but theres a few on http://ecomodder.com/ that have done it without issue and have had good results! Read up on that website, it has tones of good info on saving gas, and honestly simple stuff will get you gains. So do you research! It may even have a few people with jeeps that have done stuff that actually helped!

In turns of the jeep itself..maintenance maintenance maintenance..upgrade when possible to better parts because alot of things will help you to get better mileage as well..like injectors, free flowing exhaust..ect.

 

x2 on the champion copper plugs. Don't need to go any fancier than that

 

Looks like i have some work to do! I'll start on that next week and keep posting the progress.
Thanks for the advice!
On another note, I saw that add for GFchips on here and was wondering if
anyone has tried/used them and how it worked?