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January 2006 4x4 Tech Questions - Techline

Posted January 1, 2006

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Question: I recently purchased a '98 Dodge 3/4-ton 4x4 with the V-10. I would rather prefer the diesel, but unfortunately my current monetary status will not allow that. I have an auto tranny and 4:10:1 gears with 315 (35-inch) tires on it.

I would love to get better than my 8 mpg and was wondering what an intake and exhaust addition would do for my mpg? If the gains aren't that much, then I will save the money to put towards the diesel next year? Would a better spark plug help a little? The engine has 128,000 miles on it, and the previous owner (3 months ago) said he had just done a full tune-up, but I haven't checked for myself the trueness of his words.
Brannan L. Feldt
Hill AFB

Answer: Part of it depends on what the original owner meant by a "full" tune. I would consider changing the spark-plug wires. Buy some quality stuff, like the original factory wiring, as new spark plugs won't help if the current can't get to them. While some of the "magic" multi-electrode spark plugs may slightly increase performance and fuel mileage, it's usually in a very tired engine. Maybe there is a brand I haven't tried, but don't expect great gains from these expensive plugs.

As I'm sure you've noticed, there is no distributor cap but a separate coil for each pair of spark plugs. Because of the design, when one of the independent coils discharges, it fires two paired cylinders at the same time-one on the intake stroke and one on the exhaust stroke. There is really no way that you can test these coils.

The ignition timing is not adjustable but controlled totally by the PCM (power control module). It adjusts ignition timing based on input from numerous sources such as the coolant temperature sensor, throttle position sensor, MAP sensor, engine speed, and even what transmission gear you're in. Improper operation of any of these can have an effect on fuel mileage.

Now for the bad news: From what I have been told, while on the low side, 8 mpg is pretty common for this engine. Ways to improve fuel mileage include a very light throttle foot, synthetic lubricants-in not only the engine but all drivetrain components-and running the tires at maximum air pressure. Headers and a quality aftermarket exhaust system will help to some extent, but the payback period will be quite long.

Question: I recently purchased a '98 Jeep Grand Cherokee Limited that came with the Quadra-Trac transfer case. Normally, I have no problems with a full-time four-wheel-drive system, especially since this one has low-range, but I was wondering how hard it would be to swap it for the NVG242 transfer case? What parts would be needed?
Bill Sweitzer

Answer: It should be a pretty easy swap. In fact, it should be a direct bolt-in. However, I think that the 242 is about 1.5 inches longer than your NV249, so some driveshaft modifications will be needed. The advantage of the 242 over your present 249 is that not only does it have a "full-time" position, it also offers a two-wheel-drive high-range position for those times when four-wheel drive is not needed, with the added benefit of better fuel mileage and tire wear.

Question: I have a '98 Grand Cherokee ZJ with an aluminum Dana 44 rear. The Jeep is equipped with a 3.5-inch lift and 31x10.50 tires. I use it to tow a 20-foot boat, to haul quads, and for mild rockcrawling. I have recently discovered a horrible whine from the rear wheel bearings, or carrier bearings as I suspect. I was told by a Jeep dealership technician that repair was not an option and that the axle would have to be replaced-at a cost of over $1,200. I figured for that much money I should have more options than a stock aluminum 44 with virtually no upgradeability. I would like to find an axle that will bolt up with little or no hassle and have the strength to tolerate the towing and wheeling I do. What are my best options?
Jonathan Howe
Flagstaff, AZ

Answer: I believe I've gone over this before, but judging from the numbers of questions about this rearend, I'll do it again. Most likely, it is the carrier bearings that are bad as well as the pinion bearings. Something to do with the contraction and expansion of the aluminum housing is my guess. Yep, the aluminum-housing 44s are a real piece of junk. What makes them even worse is that it's really not a 44, but some hybrid that takes a different ring-and-pinion than the standard 44.

Your Jeep dealership is giving you some bad information. It can be rebuilt. I know it can because I rebuilt the one in my own Grand.

As far as options go, there is not much that is compatible. Ideally the rearend of choice would be one of the Rubicon Dana 44s with ABS. It should be really close to being a direct bolt-in other than the gear ratio which is 4.10:1 and it's my guess that your Grand has 3.73s. OK, 4.11s would be better for pulling your boat, so it would be a great time to switch out the front end gears.

I have heard that there were a few 8.25-inch Chrysler rearends used in the Grands with ABS, but I've never have been able to locate one. No, the tone ring for the ABS will not fit from the aluminum 44 onto the 8.25-inch axles-I already researched that with Randy's Ring & Pinion. Another choice would be a later Ford Ranger 8.8-inch as it is darn close to the proper width and is plenty strong, along with having the proper bolt pattern. Naturally, you would have to swap out the coil-spring suspension brackets, but that's not much of a problem as several companies sell a kit just to do that. Again, even though they came with ABS, it's an entirely different system that is not compatible.

If you don't mind losing your ABS, then either the Chrysler 8.25 or Ford 8.8 rearend will work just fine. And if you come up with a better solution, please let me know because you and I aren't the only ones with this major problem.

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