2.5 to 4.0 Throttle body swap. Help!! - Jeep Wrangler Forum
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Old 03-15-2012, 10:09 AM   #1
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2.5 to 4.0 Throttle body swap. Help!!

Ok, so I have a 4 banger that I am trying to squeeze a little more power out of it. I installed a cold air intake, I just installed 19 lb injectors all good. I picked up a used 4.0 throttle body out of a junkyard yesterday. Installed this morning. After install, I crank her up and the engine goes wide open. I shut it down. Try again, same thing. Everything hooked back up just like with the original. Does anybody have any ideas? Need help here.
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Old 03-15-2012, 10:16 AM   #2
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Check your iac valve, it needs adjusting. Also, those 19lb injectors won't do any good unless you have the computer reflashed. With those larger injectors the computer is just going to shorten the pulse width and your engine is getting the same amount of fuel

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Old 03-15-2012, 10:40 AM   #3
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Sorry to sound stupid, but what and where is the iac valve?
Thanks
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Old 03-15-2012, 01:39 PM   #4
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I have your answer. There is a small tab on the bottom of your new throttle body that needs to be ground off.

Same thing happened to me!
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Old 03-15-2012, 04:03 PM   #5
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Did you swap out your sensors from the 2.5 throttle body? thats all I did on mine and it works fine... Also you might want to check your clamp holding on your air intake, I pivoted mine around to make it easier to get to but it did catch my throttle linkage... kinda freaked me out until I figured it out...
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Old 03-15-2012, 04:22 PM   #6
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Figured it out. You do have swap the sensors. Done and running like a scalded turtle now. Thanks for the help.
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Old 03-15-2012, 04:57 PM   #7
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Lol, scalded turtle. Is there an improvement, then?
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Old 03-15-2012, 05:03 PM   #8
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I may have spoke to soon. Ran fine, improved power. But got home, went back out to get some gas and now sputtering, backfiring. Did not want to start back up at the gas station. Made it home. Now there is all kinds of oil in my air intake. Any more ideas?
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Old 03-15-2012, 06:54 PM   #9
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Did you hook up the vacuum lines properly? That's blow-by, meaning your vacuum system isn't de-pressurizing the crank.
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Old 03-15-2012, 07:29 PM   #10
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Not sure. Everything looks like it is hooked up. I will have to check again tomorrow.
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Old 03-15-2012, 08:58 PM   #11
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Scalded turtle.......
I think I found a new nickname for my YJ
I can't hardly stop laughing about that one....that is funny right there

It sounds like you are getting too much vacuum to the throttle body. Check and re-check your vacuum lines Especially the one coming from the valve cover
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Old 03-16-2012, 02:03 AM   #12
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What kind of improvement will changing to a 4.0 throttle body give my lil 2.5 motor? I have seen this in posts before but am unsure of what this mod actually helps.
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Old 03-16-2012, 01:34 PM   #13
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It helps improve acceleration, but the TB itself won't actually improve HP figures- you might see as much as 1hp gains. You really do need to open up EVERYTHING up and down river in order to see significant HP gains. With a high flow intake, a 4.0 TB, bored out intake header to match, borla exhaust headers and a custom exhaust you're going to see probably about 6-7hp in gains. It's enough to make a little difference but you need to do other stuff to see gains.
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Old 03-16-2012, 02:48 PM   #14
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Checked the vacuum lines. No leaks. I did install 19lb injectors a couple of days before. No issues. I swapped back the old throttle body. No more oil but still a very rough idle and sputtering/backfiring while driving. Do you have to adjust the timing at all with the19lb injectors. Also taking a while to start up. I have to give it some gas before she will start. Help please.
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Old 03-16-2012, 05:50 PM   #15
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Reset the ECM. Also consider doing a full tuneup. People would be amazed at how much can go wrong with these that causes these idle issues.
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Old 03-16-2012, 06:14 PM   #16
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How do I reset the ICM? Thanks for the help by the way.
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Old 03-16-2012, 09:15 PM   #17
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Remove the positive lead off the battery then ground it to the negative lead for 30 seconds. It will take a bit of time for the ECM to get to know the settings again.
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Old 03-16-2012, 10:30 PM   #18
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Thanks. I will try it in the morning. I am also going to check the injectors and see if I have a leak. There is a strong gas smell under the hood. I appreciate the help.
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Old 03-19-2012, 07:43 PM   #19
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Leaky injector! Problem resolved. Thanks for the help.
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Old 03-19-2012, 11:30 PM   #20
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So did the injectors with the throttle body help out? I;ve done the TB and have been shopping for injectors...
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Old 06-05-2012, 09:35 PM   #21
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I'm thinking about doing this to my 2.5l but I have a question. (dont mean to thread jack...sorry) i was wondering if after the swap, do you need a new intake rather than the stock 2.5l? If I was to buy a cai do I buy one for a 2.5l or 4.0l?
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Old 06-05-2012, 10:11 PM   #22
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I have a CAI on mine, originally bought it for the 2.5, the throttle body is exactly the same in the O.D. It is just bored out more internally so no fit problem. You just need to swap your sensors over from the 2.5 to the 4.0 you will need a security ROTC bit to do it though.
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Old 06-05-2012, 10:40 PM   #23
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Quote:
Originally Posted by Toms94YJ
I have a CAI on mine, originally bought it for the 2.5, the throttle body is exactly the same in the O.D. It is just bored out more internally so no fit problem. You just need to swap your sensors over from the 2.5 to the 4.0 you will need a security ROTC bit to do it though.
Sounds good, thank you!
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Old 06-06-2012, 08:05 AM   #24
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Sorry a security torx bit.
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Old 06-11-2012, 08:13 PM   #25
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Good info on here.
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Old 06-15-2012, 05:22 PM   #26
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How did y'all bore out the hole on the intake with out getting metal shavings in it?
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Old 06-15-2012, 08:03 PM   #27
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Never mind, I just put a paper towel in it and some painters tape, sticky side up, and bore out the hole a little and the tape caught all the shavings
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Old 03-03-2013, 05:39 PM   #28
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Quote:
Originally Posted by Xpress
Remove the positive lead off the battery then ground it to the negative lead for 30 seconds. It will take a bit of time for the ECM to get to know the settings again.
I am having the same issue as Toms94YJ.
I swapped both sensors. And reset ECM and engine goes wide open. Sits around 5500 rpm. Any ideas?
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Old 03-03-2013, 05:47 PM   #29
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All this work for ~1 extra HP.
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Old 03-03-2013, 07:03 PM   #30
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i had the same issue but its because i didnt swap out the iac. if u compare the 4.0 one to he 2.5 there is a huge difference. The 2.5 one also says "2.5" on it to help a little

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