Higher than expected for a Jeep

[zjrog]

I'd like to make it separate. Not going wheeling this weekend. Gotta work. Busy time of the year out here.

[Smoove]

I have been driving a ZJ since 1998, and I have had all three engines (4.0, 5.2, 5.9). I have kept records of every fill-up since I was 17, and my yearly average is almost always 21.4. It varied very little whether I was while living in Midtown Manhattan (and the associated traffic), driving like a cabbie, or living in the suburbs and driving like a granny. It always evened out in the end. Plus, in 2000 I stopped towing and lowered my current ZJ, and put smaller tires on for the sake of handling. It helped me gain .2mpg. I figured out my break even ROI to be 11 years. Only 3 to go!

An engineering friend of mine got me interested in areodynamics and pointed me here, albeit I am far more interested in improving the handling of my cars on the highway than mpg, and since the ZJ is relegated to 95% highway (about 7k a year) duty I figure one will help the other.

[DifferentPointofView]

finally! a guy with a ZJ that has OBDII!!!! scan gauge anyone? I kinda wanna take my mudding mileage off and transfer it. that 18mpg took down my average, now that I'm getting close to 24mpg's

[Smoove]

Originally Posted by DifferentPointofView

finally! a guy with a ZJ that has OBDII!!!! scan gauge anyone? I kinda wanna take my mudding mileage off and transfer it. that 18mpg took down my average, now that I'm getting close to 24mpg's

No scan gauge here, I use the old pencil and paper. I am not seriously considering one either, since I was somewhat forced to sell my car when we moved (we only have/can afford two spots - one for me, one for the mrs.) and while I still do need 4wd (the plows do everything in their power to bury you in), I am questioning if it is worth maintaining a 12 year old truck for the two weeks a year I truly need it. Turning your own wrenches sucks when it is 8* and you are working on 1st ave to replace a cracked header before work.

I wouldn't sweat that 18mpg, my obdI ZJ never got much better than that, even at 170k. The 5.2 never saw above 14mpg even on a trip from NYC to NC, and I bought it brand new. The 5.9 I bought as a beater and got low 18's in my four trips to and from FL.

So what can I do to improve handling? Make an underbelly tray or a front air dam that goes straight down?

[DifferentPointofView]

that'd moreover improve your aero, not as much handleing. suspension parts are the parts that are with handling, as well as tires. worn suspension parts, mostly shocks are the parts that make your handling go bad.

[Smoove]

That is a shame. I am currently running Hotchkiss springs (about 1" drop, much stiffer) Addco front and rear swaybars, Edelbrock and Bilstein shocks and a killer set of Nokian tires in a 235/60/16 flavor - hands down the best tires I have ever used. The rest is stock since it sits with 79k on the clock.

Back to the drawing board, or dealership.

[zjrog]

There is a thread on NAXJA.org about using short coilovers and 4 links front and rear on a Cherokee. I'll see if I can find that. But it is a setup strictly for lowering and handling...

[DifferentPointofView]

I'd still try a belly pan though. since your commute is mainly highway, that slightly better aero could mean 2-3 mpg's better. and do a grille block over the intake, so you can cause the intake to run hotter, making the engine need more o2, you now get less restriction because you open the throttle plate more, and reduce pumping loss at the throttle plate. It shouldn't use more gas even though your on the throttle just a little more, because the air/fuel ratio really isn't an air/fuel ratio, but an 02/fuel ratio. so you get better aero and reduced restriction.

[Smoove]

Maybe handling isn't the best term, I am looking for better highway stability and driveability. I know it is a truck, but it tends to dart around easily. I have had it for almost nine years so I am quite used to it, but my wife has a hard time of it compared to her car.

My 4.0 isn't stock, I have the 99+ XJ intake manifold (don't bother), Thorley header, cat back from a 5.9, 62mm throttle body and a FIPK. This raised my overall mpg from 18.7 stock to 21.4 I have now (averaged over the last 1000 miles). I tried a warm air intake by moving my air filter directly next to the header during winter, over 6 tanks (about 4½ months) and my mileage went down to 18.7mpg, and in mid January I switched back - it immediately went back up to 22.6 and regressed towards the mean of 21.5mpg now.

A full belly pan/air dam is in my future. Finding materials isn't easy. Finding time is harder. Much harder.

[zjrog]

Woohoo! 21.8 last fill up! So, I might just be doing something right. At this rate, I might be a little upset if I don't see a gain...