No not all 3.7 L are the same, there are minor internal timing gear differences and there are also set up differences for emissions and the cylinder heads are different depending on year
In the Chrysler's parts catalog there are four different complete 3.7 L engines listed
2003-2002 3.7L V-6 KJ Body (w/JTEC Controller)
2004 3.7L V-6 KJ Body (w/NGC Controller)
2006-2005 3.7L V6 All
2007 3.7L V6 All
As for cylinder heads
2004-2002 3.7L V-6 (right)
2004-2002 3.7L V-6 (left)
2006-2005 3.7L V-6 (left)
2007-2005 3.7L V-6 (right)
2007 3.7L V-6 (left)
For an 2002 you will need a 2002 or a 2003 engine to work correctly with no modifications
I hope that this helps you
The 2004 engine uses a different type of engine controller. This will require that the complete engine harness and controller from the donor vehicle be used in your 02 vehicle.
There are likely some other things that may need to be considered but those are the MAJOR ones off the top of my head.
Depending on the amount of internal damage you may be better off to repair the engine you have and save yourself all the hassles.
Oh, and by the way an excessive plug gap could never cause this. If anything it might be a maintenace issue with sludge and carbon build-up.
This is a PAY SITE so if I have answered your question to your satisfaction a simple ACCEPT would go along way. Feedback and Bonuses are also welcome.
I would go with the newer engine
You will need to swap the right hand camshaft timing gear from the 2002 into the 2004 for the 2002 camshaft sensor to work
You will also need to put a 2002 crankshaft sensor into the 2004 engine
When doing the swap use the 2002 fuel rail and injectors and swap all of the electrical sensors on the top end, MAP, TPS, KNOCK (under the intake), IAT, ETC,AND Idle air control, and any other bolt in sensor
This will give your 2002 KJ a slightly different emissions profile, but ultimately it should be cleaner due to the head redesign in the 2004
You do not need to swap harnesses and controllers, just make the 2004 engine appear to be a 2002 engine to the controllers and you should be fine
It is hard to say, not knowing what you have for tools and equipment or hands on experience, but if you are comfortable with the use of tools and working on cars then:
With the tear down of both engines, swapping parts and removal and re installation, with out a lift I would think that you could get it done with two solid days of work, the exhaust is going to be a bear to get apart lying on your back, be sure to use stands and safety devices when doing the job, please be safe
BONUSES are always welcome!
I suggested fixing what you have........depending on the amount of internal damage.
The other expert is the one who is suggesting making another fit. His way will break federal emmissions laws and I don't wish to be any part of that.
So, to answer your question...............the other expert will have to confirm that this will work for you because I will not.
Have a great night.
I can only advise you the same way I would treat my own vehicle.
Granted I may have a better understanding of the overall condition of the engine just by opening it up and looking at the condition of it. Is it clean? Does it have sludge build-up? etc.
Too many times I respond to questions about people doing engine swaps involving different year vehicles and there are always stumbling blocks and hurdles you have to go through to get it to run.
So........my philosophy is fix what you have or get a direct reman replacement.
As for butting in just look at the thread and you will see who answered first and whose answers contain real information and not just fluff
When you buy a reman motor from a high quality manufacturer, like ATK, they give you instructions in the crate on how to verify the new engine compared to your original and how to make the newer engine work in an older Jeep, and those where what I passed along to you
I have done this myself in the past
A high quality reman while being more costly then a junk yard motor normally will carry a very good warranty, Chrysler has a 3 year 100,000 mile warranty on theirs, and most of the other major manufactures have the same or better
List Price:5,440.00 USD
I know that you can get this from an outside vendor for much less money
Good luck with your Jeep