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When can i use 242 full time?(searched)

shortxjdoug

NAXJA Forum User
Location
Chattanooga tn
Hey guys, since both my jeeps have 231 t-cases i don't have alot of experience with the 242. My girlfriends jeep has the 242 though and i was wondering, when can you use the full time 4wd. for example...say when the roads are wet to make it a little easier to handle. I was driving hers today and was wondering. Thanks for the help
 
Pretty much any time you want.

"Four-Wheel Full Time" is essentially "All-Wheel Drive" - right down to the 50/50 torque split. Just as an experiment, I left the 89 w/242 (and a daily commuter) in 4FT for a solid year, and no ill effects.

Technically, you can use 4PT anytime there's likely to be "slippage" between the two ends - rain, light snow, sand, or whatever. Leaving your transfer case in PT on the dry and solid is likely to stretch and fail your drive chain - at the very least.

With 4FT, this isn't a problem - since it's a 50/50 split (rather than 52/48, IIRC,) between the front and rear axles, there's no difference between the output shafts to cause chain bind and stretch.

Granted, I'd not leave the tcase in 4FT for too long (the yearlong experiment was just that - an experiment. I did lose about 3mpg doing it...) because the extra drive causes some parasitic loss to fuel mileage. However, it shouldn't harm anything other than your wallet.

5-90
 
5-90 said:
Granted, I'd not leave the tcase in 4FT for too long (the yearlong experiment was just that - an experiment. I did lose about 3mpg doing it...) because the extra drive causes some parasitic loss to fuel mileage.

Interesting. I've been doing a 4FT/2HI comparison of my own for a bit, and I've noticed that mileage generally remains unaffected in my XJ. Freeway speeds (70mph) tend to dip a bit under the usual 22 (or so) mpg, but in some cases at lower speeds I've actually noticed a minor improvement.

FWIW, this is all spot measurement off of the instant economy meter on the overhead console - I'm not plotting graphs or anything like that, but the couple of tanks I've run solely in 4FT have come out with the same overall average.
 
That could be it - I don't have an "Economy meter." Granted, I did a lot of the maths between my ears while I was checking things out, but my wife is quite good at keeping records, and did a good job of co-operating with what I was doing at the time.

Of course, it's also an 89 - which means the electronics weren't as "modern" (read: painful to work on) as the later models - I'm assuming you've got a 1991-up?

5-90
 
5-90 said:
Of course, it's also an 89 - which means the electronics weren't as "modern" (read: painful to work on) as the later models - I'm assuming you've got a 1991-up?

Yep, should've mentioned it's a 2000 Limited. My understanding is that the basic guts of the factory trip computer / compass remained pretty much unchanged over the years, but it'd still be interesting to compare accuracy on later models with earlier ones.
 
True - but you had the OBD-II control electronics, vice my pre-OBD - that was the point I was making. As the OBD system progressed, they got tighter on fuel metering and efficiency.

Not complaining - I'll take my RENIX over OBD any day - small parts and sensors are easier to find, since most of them are Chevvy parts! OBD systems used ChryCo parts and sensors, which can be a little dicey sometimes. AMC = All Makes Compatible!

The trip meter and such might not have changed (although I wouldn't know, I don't have anything like that...) but that's not the key issue - the "crux of the biscuit" is the control system - and that definitely changed over the years!

5-90
 
Wow, you guys are a lot more adventurous than I. I won't go over 62-63 in FT; I just keep thinking that most states' speed limits were 55 when the (my) manual was written indicating it could be used at any legal speed. I guess it wouldn't really hurt; though I figure if it's bad enough out to need FT, I probably shouldn't be driving that fast anyway.
 
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