Every so often I see claims that the last model years of the TJ (04-06) have a less dependable 4.0 because they were manufactured with worn tooling and as a result, the tolerances are looser resulting in premature engine failure. How true is this claim? Is there any actual data showing that the last model year TJs have more engine related issues than the previous years? My 06 has 171k miles, and runs well with good compression for now. Do I need to start saving for an engine rebuild? Are these ticking time bombs?
Are the last years of the 4.0 worse?
- Thread starter adventureboss
- Start date
Never heard of this rumour before and I don't think it's true since there is no fundamental basis on it. The 4.0L engine is famous for its reliability and longevity should it is properly maintained. The downside of this motor is probably its efficiency which if you think about it comes a result of its low compression ratio, the very point that makes it reliable in the long term.
Its one of about 3 or 4 "best engine ever built".
The latter years just have junk on them like OPDAs, multiple cats, coil rails, and more and more electronics.
It's not the engine... it's everything else hanging off it in Chrysler's desperate attempt to keep it smog legal.
-Mac
It's not the engine... it's everything else hanging off it in Chrysler's desperate attempt to keep it smog legal.
-Mac
No, they are not.
Two known issues with the later year 4.0 motors with 42RLE transmission are (1) the OPDA which sometimes fails but can be replaced for a little over $100 in parts, and (2) the ECU with integrated transmission control unit that sometimes fails and causes hard shifts from 1-2 which can be remedied with a new ECU from WranglerFix for about $650.
https://www.amazon.com/Crown-Automotive-53010624AC-Pump-Drive/dp/B00NEW6GTA?tag=wranglerorg-20
https://wranglerfix.com/
Many of the negative opinions about the '04-'06 4.0 motor can be traced to one prolific poster on the Internet Jeep forums with very definite opinions that he posts over and over again without any objective evidence to back many of those those opinions. He is of the opinion that his model year TJ is the "best" and that the later model years are not as desirable.
Brianj5600
TJ Expert
The 05 and 06 are the ones that have the OPDA and PCM issues. I did have to replace my transmission control module at around 170,000 miles on my 04.
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JKP
TJ Addict
The only engine issue is the OPDA on the 05 and 06. Replace it before it seizes and drive on. Just turned 280K on my 06.
The 05 and 06 PCMs are all going to fail, AT and MT. Already had to replace mine and it's the 6 spd.
On the 05, there were issues with the 6 spd popping out of R, and there was a kit to fix that. No issues with my 06.
The 05 and 06 PCMs are all going to fail, AT and MT. Already had to replace mine and it's the 6 spd.
On the 05, there were issues with the 6 spd popping out of R, and there was a kit to fix that. No issues with my 06.
Well, he's wrong. '04 is the best model year. Furthermore, certain properties of Bright Silver Metallic paint have been proven to ward off all mechanical, electrical, and rust issues. So, unless you have an '04, Bright Silver Metallic, TJ, you have crap!
BTW, The fact that I have an '04, Bright Silver Metallic, TJ has absolutely nothing to do with these "facts".
Glad to know. I know the stuff outside of the engine is a little finicky. I replaced my OPDA before it became an issue and also somewhat recently replaced the PCM. Hoping I'm set for a while.
Those additional electronics are largely the reason why the later years also have slightly better horsepower and torque, and are actually a really good base to make significant improvements to.
The cats themselves are not a problem; they flow extremely well. However, Chrysler made a few tuning tradeoffs in the name of emissions that have some performance costs as well as higher fuel consumption. Remove some of the excess conservatism and you can get noticeable power/torque gains and still have as good, if not better, emissions profile.
There are definitely some major things that got passed over in the TJs that impacted power and fuel economy. If I had to guess, it would be because they knew they wanted to eliminate the I6 platform a couple years out. A few examples:
- The biggest one in my opinion is the choice to pair the automatic with a mechanical throttle. This should have absolutely been an electronic-controlled throttle. In manual cars, the gas pedal represents a torque demand from the engine, which the throttle position directly correlates with in a given gear. However, in an automatic, the pedal represents a given power demand, not torque, since it also affects the gear the transmission selects. Torque at the wheels is proportional to engine power regardless of gear; torque at the wheels is only proportional to engine torque in a given gear. Coupled with the fact that engines are most efficient at mostly open throttle and lower RPM, this creates a problem for tuning, in that you can either tune for performance (early shifting), or fuel economy (late shifting) but not both. Meanwhile, a car with an electronic throttle, given that the throttle and gear is partially independent of pedal position, can be tuned for both simultaneously. (Note this issue is unique to the automatics only.)
- The second biggest one in my opinion is the lack of thermal management (mostly passive) for incoming air. The TJ's stock intake location isn't terrible at high road speeds, but at lower road speeds, is pretty terrible. It also does not insulate well, especially at the intake manifold. The result is that a large amount of heat is transferred to the incoming air, making the air entering the engine hotter. Some will argue that the reduced density of air alone reduces power, and they are correct, but that is not the main issue. The bigger issue is that the hotter air means the fuel-air mixture is more prone to detonation, meaning the ignition timing has to be heavily retarded compared to the ideal timing for power. This means more fuel and air has to be burned to produce the same amount of power, thus limiting overall torque/power and reducing fuel economy.
- The third is probably the tuning means chosen to maintain emissions compliance. The hardware itself is fine, and actually quite good. The oxygen sensors, converters, etc. are all very reliable and perform well. However, there are a lot of compromises made in the tuning to protect the converters and specifically to ensure that the vehicle could pass the tests required at its time of build that affect day-to-day operation unnecessarily. For example, the PCM is designed to prevent the catalytic converters from overheating, and does so by modeling their internal temperature, and then running the engine more conservatively (timing, fueling) as the target is exceeded. This would work well, except in that the user is demanding a specific amount of power, and if they don't get the power they demand, they simply increase the pedal position. Now with the engine running more conservatively to generate the same amount of power, it is sending significantly more unburnt fuel and air to the converters than it would have in the first place, making them even hotter. This creates a positive feedback loop of the engine running even more conservatively, the user demanding more power, and the converters getting even hotter. However, this can largely be tuned out, especially if #2 is taken care of first. Run more advanced timing, and you'll have less unburnt fuel reaching the converters, and they won't reach over-temp protection temperatures nearly as much.
Know you don't have automatic, but to those that do, I replaced with Wranglerfix tuned PCM which fixed the hard 1st to 2nd shift.
No one posts a thread on this forum to say how great their TJ is running. People only start a thread when they have a problem. This leads to a skewed view as to the reliability of our 20+ year old vehicles.
If it ain't a TH400, it ain't a(n automatic) transmission!
Isn't that an electronically controlled transmission, thus completely worthless in your eyes?
"If I can't push start it, it ain't an automatic transmission.." - Zorba circa Stone Age
Isn't that an electronically controlled transmission, thus completely worthless in your eyes?
"If I can't push start it, it ain't an automatic transmission.." - Zorba circa Stone Age
Uh, no. TH 400 was designed long before the electronic bullshit. Probably the best automatic transmission ever designed.
Ever driven a modern 10R80 or 10L80? Almost as good as a CVT...
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