WJ Forum FAQ *READ THIS BEFORE YOU POST*
Frequently Asked Questions
Commonly Used Links
JeepForum.com Frequently Asked Questions
Instant build sheet directly from Jeep, no more waiting for an email back.
Frequently Asked Questions / Write-ups
Suspension / Tires
Tire Size vs. Amount of Lift Chart
Common Budget Boost "BB" Questions
WJ Suspension Info Thread
What is Death Wobble and How Can I Cure It?
Axles / Differentials
How to replace an axle shaft and/or a wheel hub bearing assembly
How to replace Ball Joints
D44a Aussie Locker Install
Warped Rotors (Front end vibrates when I apply the brakes)
A really Good Gear ratio and transmission calculator
Rebuilding a D44a axle
Engine / Transmission / Transfercase
NP242 Rebuild Tutorial
How do I replace the front crankshaft oil seal?
How do I clean the IAC (Idle Air Control) valve?
Steering Box Adjustments - How To Fix your Floppy Steering
Power windows/locks stop working
Grand Cherokee Most Common Mods
Commonly Used Acronyms
How Do I Reset the Miles to Service Display?
What are the Technical Service Bulletins for my Jeep?
Where can I request my buildsheet?
License Plate Mount for Roller Fairleads
Fluids for the Grand Cherokee
Replacing the lift struts
Double cardan rebuild (writeup w/pics)
Commonly Used Links
Spark Plugs - Thanks to Billzcat1 for this
It is generally accepted that Jeeps perform best with OE-type Champion brand spark plugs, regular cheap copper core plugs. Some people have good results with other types, but more often than not people wind up changing back to the simple, cheap Champion plugs.
Here are the part numbers and stock numbers for the plugs you need. Many stores will use stock number instead of part numbers to look these up.
4.0L: Champion #RC12ECC Stock #438, Gap .035"
4.7L: Champion #RC12MCC4 Stock #439, Gap .040"
4.7L HO: Champion RC7PYCB4 Stock #3340, Gap .040" - this is a fine-wire platinum-tipped plug. Chrysler advises that use of any other plug can cause damage to the engine.
The Champion Truck Plugs are an inexpensive "upgrade" plug for 4.0L and 4.7L owners. They have a 20% thicker copper electrode and a stronger ceramic insulator so they should last a little longer under heavy load conditions. They usually cost about $1 more than the standard and in my opinion they are a good buy.
4.0L: Stock #4412, or Stock #7034 (superceded)
4.7L: Stock #4071, or Stock #7071 (superceded)
4.7L HO: N/A
 - Champion seems to have superceded their copper truck plugs with double-platinum truck plugs and tripled the price. If you can't get the copper ones, don't bother.
The Ultimate/Unbiased I6 vs V8 Buyers Guide - Thanks to Billzcat1 for this.
The I6 is an older design with a few modern touches added to keep it "fresh". It is a solid chunk of iron....iron block AND iron head. With an all-iron construction, it is not as sensitive to temperature as an aluminum/iron motor and can survive a few overheatings. Its design is similar to the I6s dating back to the AMC days and was shared in many Jeep platforms. It's nearly identical to the motors in the XJ, MJ, TJ, LJ, and ZJ, so many Jeepers prefer this motor because it is something they are already familiar with.
Unfortunately, even the base model WJs are right around 4000lbs curb weight and 190hp/220 ft-lbs is not all that much power/torque. Even in my 3300lb ZJ, the I6 is not fast or quick by any means. Loaded down, climbing the passes means turning off OD and hanging with the semi trucks while the rest of the cars zoom on past. Off road, the low-range gear reduction negates the low power (to some extent) but on-road, the I6 is a bit lacking.
Also, Daimler/Chrysler paired the I6 up with the 42RE transmission and Dana 35 axle....neither of which has a stellar reputation for being durable. By some miracle my 42RE made it to 200k, but that is atypical and I suspect it had been replaced before I got it. Piston cracking is the most common failure of the I6 and it is more common than most I6 fans would like you to believe.
Advantages: Durable - survives neglect. Common - easy to replace. Easy/cheap to work on. Torquey - decent low end torque off-road.
Disadvantages: Noisy - old technology, sounds like a tractor motor. Inefficient - yields a massive 48hp/liter and a best 19mpg. Transmission/Axles: unreliable. Need to regear if you go with larger tires.
The v8s are something completely new that Chrysler released in 1999. They were on Ward's 10 Best Engines of the Year when they were released. They used a over-head cam design with aluminum heads, a generational leap over the previous v8s which were straight out of the 60s with fuel injection added as an afterthought. The v8 motors tend to produce better fuel economy AND more power than the I6. As for the reliability concerns - there are many well into the 200k zone. The V8s are less forgiving of neglect and do require specific coolant to prevent corrosion of the aluminum components. In addition, if overheated, the head gaskets WILL blow and the heads will probably warp. This is due to the difference in expansion between aluminum and iron and is typical of ANY engine of iron/aluminum design.
Other somewhat uncommon issues: if overheated, the valve seats can drop from the head since they are made from steel and the aluminum head expands far enough for them to drop out. The front cover near the water can become eroded from corrosion, but this is likely caused by using the wrong coolant (HOAT only!). There is a rumor that sludge is an issue, but that is a rumor carried over from the discontinued 5.2L in the Dakota and Grand Cherokee. Sludge is always possible, but with proper maintenance should not be an issue.
The V8s bring an extra 40hp and 70 ft-lbs of torque to the plate without being much heavier than their I6 counterparts. Most of the weight difference isn't in the engine though, and the engine itself may be lighter than the I6. The added weight is elsewhere: transmission and axles.
The V8 got the much-stronger 45RFE (and later, 545RFE) transmission which is still used today in the 390hp Hemi Ram. These rarely ever fail, I think I've seen two failures posted here in the last year. In addition, they added a Dana 44a rear end which is not perfect, but is much stronger than the Dana 35 in the I6 models.
Off road where torque is the king, both motors are fine. On-road is where the v8 shines. How often do you need to do 0-60 off-road? Most of the wheeling I do has an average speed of about 6mph and a top of 22 (per my GPS). But where the I6 will get you to 40mph quickly, the v8 has no problems getting up and going into freeway traffic or climbing the pass fully loaded.
Advantages: Power/Torque, mileage, stronger transmission/axles, towing capacity, won't have as great a need to regear due to higher torque, alternator/power steering pump located up high away from the ground/mud/water.
Disadvantages: not as forgiving of neglect, a little harder/more expensive to work on, not as common if you need to replace it.
4.7 High Output
This is not meant to be the ultimate 4.7HO guide, but more the "should I get one" guide.
The V8 High Output adds a ton of upgraded hard parts to the standard v8, bumps the compression, adds a forged crank, and makes an extra 30hp/30ft-lbs of torque. The nice thing is that it makes the extra torque EVERYWHERE in the power band, not just up high. In addition to the crank, the pistons, bearings, heads, valves, intake manifold, fuel injectors, airbox, air plenum, and spark plugs were also changed.
As for maintenance, the HO is no worse than the standard v8 and only has a few unique maintenance items: spark plugs, air filter, oil. The rest of the different parts are not maintenance items and should never fail in normal usage.
Lift Coil Spring Rates:
BDS 2": 200# F/ 240# R
BDS 4": 240# F/R
Claytons 4.5": 200# F/ 225# R
Claytons 6": 200# F/ 240# R
IRO 3": 175# F/R
IRO 4": 190# F/ 185# R
IRO 4.5" HD: 250# R only
IRO 6.5": 200# F/R
OME Heavy: 220# F/ ?# R
OME Medium: 180# F/ 190# R
Rusty's 4.5": 180# F/ 190# R
Rusty's 6": 195# F/ 210# R
Teraflex: 210# F/ 190# R
WJ Torque Specs - Complete List - Thanks to ChrisHager for this.
Hello people i got bored last night a nd pulled one of my extra T-Case's out of the closet and made a video. Remember this is just a video i am just showing the guts of a NP242 not how it should or should not be done or what techniqe should be used so just take it at face value and use it as a learning tool or however you should choose to use it so if you have somthin negative or some odd reason to one up me or any other poster that happens to post up do us all a favor and keep it to your self.
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