2.5L to 4.0L TB swap

[jfrabat]

OK, I finally got around to doing this. It only took a couple of minutes, and it is fairly easy.

I started by taking the old 4.0L TB that I bought on eBay and cleaned it out real good. With that done, I went to the car and removed the air hose and the 4 screws holding the TB in place, disconect the IAC and Throttle Position sensonrs, the throttle link, and then the TB itself.

Since my gaskets were fairly new (I had installed a TB Helix spacer about a month ago), I used the old ones (they were in great condition). Also, since the new TB had all its sensors, I decided not to swap them (slight mistake which will now mean I have to remove it and swap IAT's!).

When I fired off the engine, the idel started at around 3,000 RPM's, slowly dropping to around 1,600... and then it just stayed there. That's when I remembered I was suppossed to swap the IAT. Now I will have to take the 4.0L TB out, take out the sensor, and put in the sensor for the 2.5L TB. All in all, including the time I estimate will take me to replace the IAT, I'd say it will still take me less than one hour to do this.

As far a power goes, I do find a little more power below 2,500 RPMs than before, but nothing huge. But with the 4Banger, even a little increase in power and torque is a welcome addition!

Felipe

 

[Bounty__Hunter]

You can swap the IAC and IAC housing without removing the throttle body from the 'car'.

 

[jfrabat]

Well, I exchanged the IAT, but I was still getting a weird iddle. I decided to switch the Thorttle Position Sensor as well, and I am glad I did, because the one that was on the purchased TB was all dirty inside. But I think I screwed something up, because now I get an even weirder idle, with the engine going up to 1,600 RPMs and then dropping to 1,000 RPM's, and doing this cycle over and over again. The engine is also not working quite right, as it stalls when you give it gas...

By the way, I took the TB off to make the change, cause after all, it's only 4 bolts and the air hose.

Any ideas on what I may have done wrong?

Felipe

 

[Bounty__Hunter]

I did the same swap years ago, and the only 4.0L part used was the core throttle body, everything that bolted onto it was from the 2.5L TB.

Did you swap over the IAC housing, the part stamped 2.5L and held on with 4 tamper-proof torx? This needs to be done as well.

 

[jfrabat]

Yeah, I did... Only the core of the 4.0L is being used. Any ideas on what else could be? Maybe I mounted the TPS wrong or something?

 

[Bounty__Hunter]

Could be a vacuum leak somewhere as well.

Did you happen to get any solvent on any of the sensors? If so, you have to let it run a little and it'll clear up, bringing the idle down.

 

[jfrabat]

I think the TPS sensor is busted. With the engine relatively cool (as in I leave it off for about an hour), the idle is fine (about 1.1K RPM). Then, once it warms up, idle goes up to between 1.6K RPM to 2K RPM, going up about 150 RPM every 3 seconds until it reaches 2K, then droping back to 1.6K and doing this cycle over and over.

With the engine cold, if I give it some gas, it will rev up fine, but once the idle goes down the drain, if I give it gas, it stalls. To drive it home, I had to have a VEEEEERY light foot, as it would rev up as long as you did so just a tily little bit at a time (I was feathering the clutch much too much for my taste, but it was either that or paying for towing!).

I got a CHECK ENGINE light driving home, but I had to return to work, so I did not have time to read what the problem was. But I'll check that tomorrow (I think the odds of it being the TPS are high). I still have the TPS from the 4.0L TB, so I can try that one first (if the problem IS the TPS), and if it does not work, I can always get a new one and replace it (the one on the 4.0L TB looks a bit beat up!).

I also know my fuel system is not up to par (when I removed the injector rail because of damage, it was filled with slidge), and I do plan to (1) clean and seal the tank (I got a POR-15 kit for this purpose), (2) replace the fill and vent lines, (3) replace the fuel pump and in-tank fuel filter, (4) replace the in-line filter (I did this about 2 months ago, but it looked like it was NEVER replaced!), and (5) replace the fuel rail, FPR and fuel injectors. I already got all the parts (about $300 worth!); now I only need to find the time (just the POR-15 tank tratment takes a good couple of days to do because of all the waiting time involved!). But I know this is not the problem, because before the TB swap, everything was working OK (as long as the temp outside was belos 85 degrees!).

Felipe

 

[jfrabat]

Well, I guess I have something acting up; if I install the 2.5L TB, the engine runs OK until about 4,000 RPM's, where it starts to stutter and will not go past it. With the 4.0L TB on, the idle is acting up, and the engine will not rev up propperly (I get a lot of smoke from the exhaust, some backfiring on acceleration, and stalling when flooring the gas pedal).

Keep in mind that neither the TPS or the IAS are the problem, as I replaced them thinking it was them that were acting up. I also replaced the O2 sensonr about a month ago. As I mentioned, I know my fuel system is not up to par, but in your opinon, is this the problem, or is my problem somewhere else? Opinions extremely welcome at this time...

For the time being, I have uninstalled the 4.0L throttle body, as at least with the 2.5L TB I can run the Jeep to work and back (even if I cannot accelerate to 4,000 RPM's, regardless if I am in gear or just revving up the engine on neutral).

Felipe

 

[currupt4130]

Did you reset your computer after you did the swap? It may need to relearn the fuel curve with the new throttle body on there.

 

[jfrabat]

I did not reset it, but I did drive the car around for some time, so the computer should have had enough time to relearn the the fuel curve.

Felipe

 

[jfrabat]

I think that now that I have upgraded the fuel system (cleaned tank, new pump, new filter, new fuel rail, new fuel injectors, new Fuel Pressure Regulator), I will give the 4.0L TB a second try... Maybe now it will idle correctly. I will also disconect the batery to make sure the computer resets, and see how it goes. Any other sugestions?

Felipe