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Discussion Starter · #1 ·

Here is my swap that I am doing and I have a few questions on it

I have an 89 2.5L with the crummy but reliable Throttle Body Injection system (T.B.I.).

The motor has 128k hard miles on it and is very tired and has low PSI in all cylinders!

I am going to be picking up a nice 2.5L and an AX5 from a 97 TJ very soon and I am looking into installing it with the nice and newer Multi Port Injection system (MPI).

The motor is complete with all EFI, Computer and etc…. It doesn't have the ENTIRE harness but 99% of it is there.

My questions are this:

-Which fuel pump would I need?

-Is the one from a 91+ 2.5L with MPI the same as the TJ ones? Do they produce the same PSI? I am assuming I need a new tank from a 91+ YJ as well to accommodate the new pump and sender unit. I know that the MPI and TBI ones are different and these put out different PSI's

-Would I be best of using the wiring harness from a 91+ 2.5L YJ instead of the TJ one? The AX5 I am getting has the CPS for the newer MPI! What are the changes with emissions and such with the TJ?

-What, if any are the differences between the YJ and TJ MPI?

-Sensors? Brackets? Etc..

Anyone done the TBI to MPI swap before??

Any small things to look for??

Any info or tips would be great!!

Thanks a lot!!

Boston Mangler
89 YJ With A Bunch Of Goodies
See It At:

Discussion Starter · #2 ·
You need the high pressure pump from the donor, your current pump is low pressure. You shouldn't need a new tank, just remove the brackets from the donor and they should fit on your tank sending unit, unless of course the donor has a different/larger tank than yours. The only problem you might have is if the fuel pressure regulator is in the tank instead of the fuel rail, if it is I would try and get an earlier computer and wiring harness, on the newer TJ's they started to incorporate the computers to monitor everything on the vehicle, if it was me, I'd try to use the harness and computer from a 91 to 95, anything newer you might have problems with the wiring harness, hope this helps you out.



Discussion Starter · #3 ·
Just curious...why keep the 2.5L? Why not spend all that money on a 4.0L that has everything there? Just a thought.


'88 YJ, 4.2L w/Weber 32/36, Procomp 4" w/33 BFG M/T's, TFI upgrade, Stock auto tranny and everything else.
I love bein' a Jeeper!!!
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