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Old 04-10-2012, 09:34 AM   #1
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Lightbulb Thottle body swap. 2.5L to 4.0L TB

Trying to get more air into my engine and i hear this is a pretty well liked mod. Swapping out the 2.5TB for the 4.0's. If anyones done this before, id like to hear some feed back,problems you ran into, How the install went etc.

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Old 04-10-2012, 09:59 AM   #2
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There are a lot of write-ups floating around on it. Search is your friend.

Overall, it should be a simple swap.
4 bolts, swap the sensors, new gasket, disconnect the battery to reset the ECM

If you want to go advanced, you can:
bore out the throttle body up to 62mm
add a bored spacer and
bore the port on the intake manifold to match
open up the air box

There have been reports of power loss to no improvement to 20 hp increases.
Some say it bogs down, others say throttle response is greatly improved.
Your mileage may vary, but it is easily reversible if you have any problems with it.

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Old 04-10-2012, 12:41 PM   #3
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So i do not need to bore anything out, it is merely another option? also, if i wanted to buy a spacer or a CAI would i now need to get one for a 4.0?
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Old 04-10-2012, 12:50 PM   #4
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boring is optional, so is the spacer, which should be for a 4.0

some of the CAIs mount differently based on the engine
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Old 04-10-2012, 01:16 PM   #5
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ok thank you
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Old 04-10-2012, 01:47 PM   #6
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What year is your 2.5L? Everyone skips out the park that this will not work on 87-90 2.5L engines because they use a ghetto Throttle Body Injection setup (TBI) where there is one big injector inside of the throttle body. The 4.0's use a Multi-Port Fuel Injection (MPFI) system that uses 6 separate injectors on the intake manifold themselves that spray fuel almost directly into the head block from their positioning. The 4.0 throttle body is basically just a butterfly valve with a couple of sensors, no injector mounts. Completely different from the 2.5L TBI unit.

However, on 1991-1995 Jeep 2.5L engines this will work as they use a MPFI system like the 4.0's, and utilize a similar throttle body (albeit it's a bit smaller).
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Old 04-10-2012, 02:04 PM   #7
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His profile has it as a '95
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Old 04-10-2012, 02:07 PM   #8
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In which case it will work but since he hasn't exactly specified (since a lot of us have more than one jeep...) it's up in the air still...
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Old 04-10-2012, 03:03 PM   #9
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Make sure to swap the valve on the side held in by tamper-proof bolts(can't remember it's name), or it will idle at full throttle, lol. Other than that is is a bolt on and go swap. Have done mine and everyone I know with a 2.5 has done it too.
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Old 04-10-2012, 06:27 PM   #10
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Does this swap give you more hp just curious
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Old 04-10-2012, 06:37 PM   #11
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Its hard to tell, but I know I can pull hills better than I did before the swap, and I can lug the motor a little more...
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Old 04-10-2012, 10:01 PM   #12
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Quote:
Originally Posted by Florida yj View Post
Does this swap give you more hp just curious
HP increase is somewhere around 2-3hp. Primarily it gives better acceleration.
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Old 04-10-2012, 10:20 PM   #13
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Thanks, I think I'm going to keep my eye out for some parts and try it. How many sensors do you have to replace?
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Old 04-11-2012, 11:53 PM   #14
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Mine jeep is a 95 that's correct
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Old 04-12-2012, 12:51 AM   #15
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Been wanting to do this too. I bought my jeep not to long ago the po did a few mods to the motor. Is there a way to find out what tb i have by just looking at it without unbolting stuff?
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Old 04-13-2012, 03:27 PM   #16
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Quote:
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Thanks, I think I'm going to keep my eye out for some parts and try it. How many sensors do you have to replace?
None, just the valve on thee side as notedd in my previous post, it be called an AIS.
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Old 04-14-2012, 10:12 PM   #17
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I don't see how boring is optional, if you put the 4.0L on the unported intake , what exactly have you gained? I will do this to my 'angry squirrel' motor in stages, for before and after. Wish I had a dyno in my garage...lol
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Old 04-15-2012, 11:52 PM   #18
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Quote:
Originally Posted by YJ325i
I don't see how boring is optional, if you put the 4.0L on the unported intake , what exactly have you gained? I will do this to my 'angry squirrel' motor in stages, for before and after. Wish I had a dyno in my garage...lol
This too has puzzeled me. I don't get if the two tbs are the same size why am I swapping them
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Old 04-16-2012, 12:04 AM   #19
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The 4.0 TB is much larger than the 2.5L TB. The restrictions come from the intake manifold which you can file open a bit more for bore it out or something.

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