Originally Posted by howellru
Thanks for the techauthority link.
Last topic, I promise.
I'm considering replacing my YJ's 4.2L with a TJ's 4.0L fuel injected engine and have a couple of questions.
1. Would there be a noticeable improvement in performance and fuel effeciency?
2. Would the 4.0L bolt up directly up to my Yj's transmission and drivetrain?
3. What other hurdles and expense would be involved in such a swap?
This would be a big improvement, but remember the 4.0L has a shorter stroke than a 4.2L, so a 4.2L can theroteically be made to produce more torque than a 4.0L. Fuel economy may be a wash, or a slight improvement since a YJ is lighter than a TJ. It will bolt up to your transmission, but if you have the BA10 it may not stand up to the power increase, plus you may have an issue with mounting a crank sensor.
A couple of thoughts - get a complete engine/trans/t-case from a 1991 or newer YJ, as well as the computer to make the bolt-in easier...no issues with flywheel/crank sensor, etc.
Install the Mopar fuel injection kit on your 4.2L. Complete kit that is a bolt on and the simplest way to go.
Put a 4.0L head/intake on your 4.2L. The 4.0L head (especially the H.O. head from the early/mid '90's) flows much better than a 4.2L head.
Any of these options will be expensive, unfortunately....although a complete drivetrain from a 91 YJ would probably be the cheapest way to go if you get lucky and are in the right place at the right time.