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foxinthemudd 03-10-2008 12:12 AM

intresting info on the 4.0L TB swap...
I was lookin around on the net tonight searching for aftermarket cam info and ran across this...

After reading the article on the 2.5L to 4.0L throttle body swap, I noticed one detail that was not even mentioned, changing the A.I.S motor and housing to the new throttle body.

First, let me say hello to the group. I am a tech for Jeep and Chrysler, electrical and drivability are my areas of expertise. Now I'm going to add my .02

1. I have done this mod on my own 92 wrangler with a 2.5L engine with incredible results. The 2.5L has a K&N stock replacement air filter w/ a stock air box... the restrictor in the air box cover removed, a tri-y design header (manufacturer unknown, was given to me), stock exhaust minus the cat, an Accel super coil (direct OEM replacement) w/ Belden spiral core wires and factory plugs gapped at .035". I have 4.10 gears w/ 35x12.50 General MT's and I can say this motor screams. The motor in stock form would not pull the jeep w/ 33" tires. I did all the mods except the throttle body and put the 35's on. At 65 mph into a 15mph headwind, I would have the throttle pushed to the floor just to maintain speed in 4th gear, with the throttle body swap, it was like putting a 4.0L under the hood. Under the same conditions,I could maintain speed w/ 1/4 to 1/3 throttle opening, and my DRB III confirmed it. It felt like I added 15 to 20 hp., bottom end torque improved and overall drivability improved. Fuel milage remained constant, or slightly better depending on how heavy my foot was.

2. Now on to the AIS motor. If you look at the AIS motor and housings on th 2.5 and 4.0L engines, you will notice tha the idle air passage seat where the AIS needle seats is considerbly smaller on the 2.5L than the 4.0L, so is the needle on the AIS motor itself. You must transfer the AIS motor and housing from the 2.5L throttle body to the 4.0L throttle body, if you don't and you use the 4.0L housing and motor, you may not get your idle speed down to where it should be. Your AIS motor will be fully closed or close to it (0 to 2 steps). On TJ's this can be a problem with the OBD II, since it can trgger a code in the PCM (target idle not reached), so be sure to transfer it to the 4.0L throttle body. Be careful with the gasket it is not available separately. If done right and you have access to a DRB II or DRB III or a code scanner your idle steps should be around 14 to 18 steps in neutral, air off, if not you can fine tune to get it in that range by adjusting the throttle stop screw, if you turn it more than a 1/2 turn in either direction, you better check your installation.

3. Yes you do have to trim the intake manifold opening, mine had a 1/8 lip around the base and it does have a profound effect on air flow, enough to cancel the gains of doing the conversion. I used a die grinder with a wide fluted aluminum bit, on the vehicle wuth rags stuffed in the intake runners. A shop vac to remove the filings was used and make sure all filings and rags are removed. I trimmed the hole to the size of the gasket (4.0 and 2.5L gaskets are the same).

4. The PCM's adaptive memory after 100 miles of driving was practically unchanged after the swap meaning the PCM saw no ill effects from the swap. Keep in mind that the MPI fuel injection is a speed/ density based system and does not see an increase in airflow like other systems that use a mass air flow sensor, instead it sees changes in MAP value and intake temperature (density in the intake manifold) crankshaft speed and throttle position, coolant temperature in all modes plus the O2 sensor at idle and part throttle and then using complex alogrythims calculates the injector pulse to provide the correct fuel/air raio. For all practical purposes you do not need to worry about it, the computer seems to compensate for the swap with no problems.

5. For those of you who still feel the need for more fuel, you can try injectors from a 4.0L engine. These run approx. 10% richer, single cylinder displacement is about 10% larger on a 4.0L, so these will work good if you need more fuel delivery without screwing around with the pressure regulator on the fuel rail (91-95 only, TJ's regulator is in the fuel pump). The PCM will only compesate for the added fuel in closed loop operation only (idle and part throttle)!

I did this swap months before I even came across this site (my own idea) in search of more power, knowing what it would take to install a 4.0L in my Jeep, even with the resources available, and I can tell you I am very satisfied with the results. I hope the information I posted is useful and can be used to your advantage.

I got to readin and thought I'd post it up as some more helpful info for us 4bangers..

Dare2BSquare 03-10-2008 08:04 AM

I wouldn't say it feels like a 4.0, but I can tell a difference in highway cruising performance in my auto. It is much easier to maintain speed. Fuel economy is about the same as before the swap.

4.0l sahara 03-10-2008 02:44 PM

Did you look on summit for the cam? It's the right one but is marked wrong. It says under details it's for a sohc but it's the correct one. It has like 460 lift perfect for a dd.:D

4.0l sahara 03-10-2008 02:50 PM

I'm planning on the accel coil and a cam for my 4.0.:punk:

foxinthemudd 03-10-2008 07:18 PM

ya I don't know about the cam. I've never done that amount of work with sensitive areas like that before if I do it will be a while in the distance so I can save up for the parts (and find the time) to do it. I'm thinking about just doing the bigger wires and dist cap and rotor along with doing this, grinding out of the manifold area for the 4.0L TB and removing the spacer I have in the jeep right now.

4.0l sahara 03-10-2008 08:09 PM

:DIf i'm only 16 and have done a few cams and rebuilt a few old motors and a few modern ones. I think you should be able to do it. To me stuff like that is fun I like measuring all the stuff.

foxinthemudd 03-10-2008 09:05 PM

ya, but I hate math and measuring things out... thats why I didn't stick around in the remodeling construction business very long, however it was fun :D I'll probably do it but not for awhile.

jgwalt 03-10-2008 11:19 PM

hey foxinthemud, i did the 4.0 throttle body swap on my 94. i noticed a bit more low end pull and its definitely better on the highway. but sometimes it idles a bit high, like around 1500 rpm er so. i cleaned the ais motor from the 2.5tb and changed it over, i also changed the tp sensor. did i miss something? or do i just need to wait a little longer for the computer to adjust? any ideas?

foxinthemudd 03-10-2008 11:24 PM

try changing out the MAP sensor. I was idling around 1800 after I did the swap changed the MAP and good to go. I noticed some better throttle response after I did the swap but that was about it.

and Welcome JG

I'm gonna go pick up some Dremmel grinders this week and grind at the manifold so I'll get back to you guys about doing that part and we'll see how it works out.

jgwalt 03-10-2008 11:31 PM

ok cool, i'll try that as soon as i get some extra cash! would an adjustable map sensor be a prudent purchase?

foxinthemudd 03-10-2008 11:37 PM

I don't know much about them, I just went with one from a scrap yard... post another thread and ask. I'm sure someone knows about them.

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