Originally Posted by Jeffy
There were a number of reasons. The engines (4.2, 4.0 & 2.5) were used for Jeep exclusively. Dodge did share the 2.5L calling it the Magnum for a little while in the Dakota though. Unfortunately it was a dead end design-wise. If they wanted more power and better emissions they would have had to design a new engine from the ground up or pilfer from an existing engine platform. This would consolidate the number of engines they use as well. Most of the Chrysler/Dodge and Jeep line-up had already transitioned to the new Powertech engines by 2002/3. That left the I6 Wrangler the sole vehicle left that was still on the old I6 Powertech. The I4 Wrangler was already using the new 2.4L Powertech. The 3.8L was borrowed from the Pacifica and the Minivans. And while it's an OK engine, in something like the JK Unlimited Rubicon, it was underpowered to say the least. The original 4.0L made 240 ft-lbs and the 3.8L made about the same. Peak torque came up almost 1000 rpm sooner, 3200 rpm vs 4000 rpm (4800 rpm (3.6)). Also the older TJ's weighed less; 3,092-3,832 lbs vs 3760-4129lbs.
I think the 4.0 was available in the WJ Grand Cherokee until 2004 as well. The 4.0 is an unbelievable engine. I sold an Accord to a dude that had an XJ with the 4.0 that decided he needed something new since the XJ was at roughly 375,000 miles; and the only thing wrong was the oil pump needed replacing
That kind of longevity is as good or better than anything on the road! I'm amazed that after last weekends trip of over 800miles with about 100 of those being off road my nearly 20 year old 4.0 didn't even use a drop of oil!
To say ditching the 4.0 was a mistake by many is probably a bit harsh. The basic engine design was 40 years old at the time it was retired. About every bit of power, economy and efficiency was tapped by the time it was retired. I don't think any other auto company was using a design that old at that time. The saddest part was that the plant that manufactured those engines, had been in pretty much continuous operation for like 100years and once Chrysler stopped making the 4.0 the plant only remained open for a few more years making those less than stellar mini-van engines and then closed forever.