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January 2006 4x4 Tech Questions - Techline

Posted in How To: Tech Qa on January 1, 2006 Comment (0)
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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.

Question: I am trying to get my oil pressure up a bit in my 401 V-8. I have some information about gasket thickness being part of the contributing factor for low hot-oil pressure. What is your take?

I remember the first time I fired the engine I broke the distributor gear because I didn't use a gasket at all-just gasket sealer, which bound up the pump. So I have to take it apart again and I will try and see if I can get some different thicknesses of gaskets, if that's what I should try. I moved to 20/50 in the engine and it didn't boost it too much. It looks like the pump is nice and tight to the sides of the oil-pump chamber, and it doesn't look like much scoring inside either. This is a high-performance engine with very low mileage.

Answer: What? You broke the drive? That means the engine either ran or cranked over without any oil pressure! Shame on you-you're supposed to first spin the pump as you assemble it to make sure it is not binding! After that, I like to pack the pump in Vaseline, not grease, as this eliminates any air and makes for a better prime. You did pressure-lube all the oil passages before you started the motor, right?

AMC and Buick V-motors all have oil delivery problems due to the external pump, long passageways, and too-small oil channels. On the Buicks, we would drill and blend the oil holes from pump to block, and make up a spacer plate that, of all things, used gears from a 409 Chevy that were about a third longer. Oiling was one of the biggest problems that Team Penske had when they ran AMCs in TransAm races. They did a lot of development work to make the engines live.

Pump clearance is an important aspect of oil pressure as well as engine clearances. Start with the pump first. It's been a long time since I worked on an AMC engine, but as I recall, there should be about 0.001 to 0.002 inch of clearance on the sides-maybe even as low as 0.0005 if you can get it, but that is hard to measure. Use a narrow feeler gauge between the housing and the gears, not a wide one, to ensure accuracy. You should rotate the pump in the housing and check each gear for proper clearance-maybe even at different spots in the housing. I have seen new gears not cut equally on all the teeth. Examine the housing real closely. It doesn't take much wear or scoring in the aluminum housing to gain clearance and lose oil pressure. You may end up buying a new pump, gears, and/or a housing/timing cover. Believe it or not, I have even seen a difference in clearance with different brands of gears. Remember, we are talking about tight clearances here.

Measuring the cover clearance is a bit more tricky. I like to use a piece of Plastigage across the top of each gear, then put the cover on and tighten it down, and then measure the flattened Plastigage with the scale provided. You can use a feeler gauge and a straight edge for this, but it's hard to get an accurate measurement. The clearance should be about 0.002 inch for the best oil pressure. Excessive clearance can be reduced by filing the pump housing to remove some material, but if you have to do this, do it very carefully in order to maintain a flat surface. Better that it be put in a mill and machined off, but that's a real pain to make a fixture to hold it in the proper position.

If you don't have enough clearance, then it can be gained with different thickness of gaskets. You want to use a fairly hard gasket material to limit compression and a change in clearance.

Be very careful using any type of sealer on an oil pump. If you do use a sealer, run a flat mill file over the pump-housing sealing ends to make sure it is square and true. Careful here-it has to be flat and true. The small lines hold the sealer in. Then use some type of gasket sealer, like "Copper Coat" in a spray can. If you're real careful, you can use a thick layer of Aviation Permatex, but you sure don't want to get any excess into the pump.

Also remember that there is a relief valve. Make sure it is not sticking in the open position and allowing oil to flow back into the pump. It most likely has a spring that is set for somewhere around 65 to 75 pounds. This doesn't mean that the pressure will be that high-it is just that it will open at that high, like on a cold-morning start with heavy oil.

If for some reason you think that you need more maximum oil pressure, don't stretch the spring. Use a shim, or maybe like washers, between the screw on the cap and the spring. But remember, it's the pump that makes the pressure.

In reality, all you need is about 10 psi for every 1,000 rpm or so. However, you don't want to load an engine hard at, say, 2,000 rpm and only 20 psi, as this will actually cause oil shear. Part of the oil pressure that the bearing sees is from the hydraulic wedge effect of the crank turning and trying to get closer to the bearing from the imposed load.

If the pump checks out properly, then the low oil pressure could be from too much rod or main bearing clearance, including side clearance on the rods. Excessive side clearance will let too much oil bleed out. This can depend on just how careful in taking measurements your engine builder was.

It could be that you "added clearance" to the engine when you cranked it without oil pressure. It doesn't take much, especially with a performance engine. My father-in-law, who was an engine builder of note, was a real stickler on always pressure-lubing an engine before starting, making sure that he would have oil pressure showing on a gauge, and the engine should fire, like, right now! He saw many of his engines damaged by lack of oil pressure when first started.


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