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2.5tbi to 2.5mpi motor swap?


NAXJA Forum User
Hello this is my first Jeep its a 1990 XJ
I have been tring to buy a jeep for a long time but money didn't allow me to buy a ready to to drive one.
I bought my Jeep with a bad motor and found a great deal on a 1995 2.5 mpi motor i got the computer and most of the wiring.
now I can switch a motor if its the same to replace, but all these wires? What i would like to do is switch the mpi intake with my old tbi intake and use my old wiring harness. Is this possiable?
will my gauges work? Any advise will be very appreciated
The engine is the same. The electronics are totally different.

The 1990 was the last year of the Renix injection/computer system. In 1991 Chrysler changed over to a Chrysler designed and manufactured multi-port injection, which is what's on your donor engine. The two systems have essentially nothing in common.

The lack of compatibility is so bad that even the gauges work in reverse. I had a gas gauge in an '88 (also Renix) that was pegged way beyond full. Testing showed that in the Renix years an open circuit on a gauge sends the gauge all the way to the right. (Same thing happens with the temp and oil pressure gauges).

In the Chrysler years, if you unplug the sensor (open circuit) the gauge drops to zero. Also, the resistance range for the sensors is different. Renix is 0 to 80 (or 88) -- Chrysler is 5 to 105.

The multi-port 2.5L would be a nice upgrade, but you need to do some exploring of wiring diagrams. I see no reason why you can't run the engine from the new computer but retain your existing gauges -- just swap in the sensors from your old engine. But please do some research before taking my word that it can be done, 'cause I don't know for sure.
MPI uses a higher pressure fuel pump as well

if you're going to go to all that effort... consider adding two more cylinders in the process. It's literally the same amount of work.

and ALWAYS if possible, get an ENTIRE VEHICLE when doing an engine swap of any sort. You'll run into all kinds of strange little differences, and weird parts that need to change
If you put your TBI on the new engine I would be intreested in the computer and wire harness for the MPI set up. I have an MPI engien that will be here this week and cannot decide if I'm going to try and make it work or go with the bored TBI that I have.

As eagle says the electronics are different. But with enough will power it can be done. Get a wiring diagram for each vehicle and the gauges out of a donor to go along with the wiring harness. It's not as hard as you think to rewire, just takes time and patience. I rewired my 2.5 from carb to tbi. Fortunately for me the gauges still worked with the new computer. I had to run one hard wire to the fuel pump. You will need a different fuel pump though as the mpi needs a higher psi. Good luck!
How come I knoew you would put your .02 in on this thread!

I guess I'm too predictable. Anyway I have a soft spot for anyone man enough to drive a 2.5l.
Re: $.02

HossHoffer said:
I guess I'm too predictable. Anyway I have a soft spot for anyone man enough to drive a 2.5l.

Especially if it is a 1984 carburated one, like mine!