View Full Version : 2.5l <> 4.0l tb swap

01-14-2010, 08:19 AM
I've been driving around a 91 yj while the xj motor gets finished and
while the 2.5l gets fuel economy that is stunning..it's a dog
..6 screws ...4 bolts later ...the tb swap took all of 10 minuets
(4 of those were drinking beer)

Worth it...open up from 3-5k rpm as useful hp, and I can sit on the highway in 5th (with 31s) and still roll on the pedal without a down shift
(which I used to have to do for the mildest hills to hold 100kmh) it'll even
idle up a hill in 1st (idle's at 900rpm now)

total cost 0$ (I had a spare tb from my 2000 intake manifold swap on my xj)

1: take off intake box
2: disconnect idle air valve and throttle position sensor
3. unbolt 2.5l tb and get out your torx bits
4. swap iacv and tps from 2.5l TB to 4.0l tb
5. bolt 4.0l tb onto intake (with 4.0l tb gasket)
6. hook up iacv and tb and reinstall airbox
7. key on..no check engine light?

click varoom

01-14-2010, 07:26 PM
does it matter for the year of the 4l tb becuase i have a 88 2.5 and its ball less and i have 3 4.l motors all diffrent years so does it matter

01-14-2010, 07:32 PM
It will not work for the 86 to 90 2.5L engines. 86 to 90 2.5L are Throttle Body Injected, basically an electronic carb, 1 big injector mounted right on the throttle body and a couple of sensors. 91 and newer 2.5L and all 4.0L engines are Multi Port Injected, the throttle body is just an air valve with a couple of sensors and the injectors are mounted in the intake manifold runners

01-14-2010, 07:35 PM
I think if your 88 is renix/mpfi it's a 3 bolt tb from a 4.0l pre-88
but if it's tbi like nutbar said your hooped

01-15-2010, 08:31 AM

01-15-2010, 07:27 PM
take a picture of the throttle body and intake and we should be able to give you a better answer