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General Forums => The Mess Hall => Topic started by: jfrabat on January 05, 2008, 07:28:48 PM
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I had noteiced that between the e-fan, the auxiliary lights, and the Air Conditioner fan (which surprisingly, drains A LOT of energy!), so I got a 165A Load Boss alternator (I found them on e-bay) and installed it today on the Jeep. I also installed a bored out 4.0L TB (it is now 62mm) and actually got it to work, but I got a question about this that maybe you can all help me with...
On my rig, the idle has always been a little high (800~1,000 rpm). With the new TB, the idel has kept at the same level, but I noticed that if I start the Jeep without connecting the wire for the IAS, the idle goes to a more "normal" level (about 600~700 rpm), but, of course, I get the CHECK ENGINE light. By the way, all the rpm readings are taking from the dash, so they may not be anywhere near as exact as I would like them to be... Anyway, is there any way to make the computer lower the idle speed, or is that impossible? I know you can open the TB with the hex screw, but mine is already all the way closed, so that has been adjusted as much as I could already.
By the way, for those of us that are always debating the question of how much power the 4.0L and the TB spacer ads, check out this link (http://www.creeperjeepers.org/throttle%20body%20swap.html) I ran into... It seems the TB spacer does ad power, but more this is the result of lowering the temp, not improving flow. This is all news to me!
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Usually a high idle is caused by a vaccuum leak. I've never had to track one down but I think the technique is to spray carb cleaner on the vaccuum lines to see if it causes a change in engine RPM.
BTW, how noticeable is the horsepower gain with the 4.0 TB?
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Usually a high idle is caused by a vaccuum leak. I've never had to track one down but I think the technique is to spray carb cleaner on the vaccuum lines to see if it causes a change in engine RPM.
BTW, how noticeable is the horsepower gain with the 4.0 TB?
Don't spray carb cleaner at a running engine, you use an unlit propane torch to safely find vac leaks.
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What kind of problems could the carb cleaner cause?
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What kind of problems could the carb cleaner cause?
A rather large fire
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Ok, won´t be doing that!
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Usually a high idle is caused by a vaccuum leak. I've never had to track one down but I think the technique is to spray carb cleaner on the vaccuum lines to see if it causes a change in engine RPM.
BTW, how noticeable is the horsepower gain with the 4.0 TB?
TB HP gain is not too significant, but it is there. And I agree with Neale on the Carb Cleaner!
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Sounds good. I bought one a while back on ebay but haven't gotten around to putting it in. Thanks
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By the way, I think the idle issue is the computer learning the new mixture curves (more air is now coming in), cause the throttle is slowly going down back to normal levels.
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Does anyone know the thickness of the 4.0 TB spacer. I want to build one?
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jfrabat,
Did you swap out the 4.0 liter idle air valve with your 2.5 liter IAV when you installed the 4.0 liter TB? The 6 cylinder needs more air, so the IAV allows more flow. I have the stock 4 liter TB (60mm bore), TB spacer, with the 2.5 liter IAV and the 4 banger seems to idle at a normal speed. If you swap the ide air valve, be careful not to damage the gasket, otherwise you'll have vacuum leak.
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Does anyone know the thickness of the 4.0 TB spacer. I want to build one?
The ones I've seen are 1".
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I just pulled a 4.0 Liter TB out of the junk yard (literally an hour ago). I just finished cleaning it up. I read the article from the link at the top of this post and decided to upgrade to the 4.0 TB. That is about as far as I got. I manage a local machine shop and was just going to build the spacer. I guess I'll go with 1" and let you guys know how it turns out.
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Did you swap out the 4.0 liter idle air valve with your 2.5 liter IAV when you installed the 4.0 liter TB? The 6 cylinder needs more air, so the IAV allows more flow. I have the stock 4 liter TB (60mm bore), TB spacer, with the 2.5 liter IAV and the 4 banger seems to idle at a normal speed. If you swap the ide air valve, be careful not to damage the gasket, otherwise you'll have vacuum leak.
Yes, I did. The idle does go back down to normal (well, to what it was before the TB change, anyway, which is about 900 RPMs), but when you get off the highway, it takes a couple of seconds to come all the way down. It starts at about 1,500RPMs, then dropes to 1,200RPMs within 5 seconds, then it takes it about 20 seconds to go all the way down to 900RPMs.
Does anyone know the thickness of the 4.0 TB spacer. I want to build one?
The one I have is 1" tall, and the bore is 62mm.
Felipe
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If you haven't already done so, clean the throttle plate (butterfly) and AIV with a good spray cleaner (like Gum Cutter). Lube the throttle cable and make sure it's all moving freely.
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I have the stock 4 liter TB (60mm bore), TB spacer
I believe the stock 4.0L TB is a 55mm bore. One of the greatest improvements to boring out a TB is removing the taper below the throttle plate, making throttle response instant. In stock trim, the throttle plate has to move 1/4" or more before any air gets between the throttle plate and the tapered bore beneath the throttle plate. Look down the neck of the TB and move the throttle, see for yourself.
I've got a comparison pic over in the classifieds section comparing the 4.0L TB to the 62mm TB's I'm now selling (cheap). I've also got 62mm spacers.
jfrabat, I would remove the IAC housing and clean it thoroughly, along with the IAC plunger. If that doesn't work, try installing a different IAC plunger assembly. Mine idles at around 6-700 with a 62mm TB.
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I believe the stock 4.0L TB is a 55mm bore.
I always thought it was 56mm, but I guess both are too close to call!
Ijfrabat, I would remove the IAC housing and clean it thoroughly, along with the IAC plunger. If that doesn't work, try installing a different IAC plunger assembly. Mine idles at around 6-700 with a 62mm TB.
Yeah, I did that... And adjusted the hex screw that adjusts the throttle plate (I forgot to do that the first time I installed the 4.0L TB, which is why it was idling at 1,500RPMs then!). And I installed a new plunger. But I'll clean it again just in case. I do think it is possible that I have a vacuum leak somewhere, though, and that could be the culprid.
But the idle is now at the same level it was with the 2.5L TB, so I am pretty sure it is not the TB that is causing the higher idle. It does take it a couple of seconds to bring the idle back down when getting off the freeway (as soon as you let go of the throttle, it is around 1,300RPMs, but then goes back down to 900).
Felipe
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Could be bad seals on the throttle shaft bearings, if not leaking anywhere else.
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spray around the throttle shaft and throttle body with propane or some brake cleaner even a spray bottle with water works to find vacuum leaks
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I gave this some more thought, are you sure you have the correct IAS housing for the 2.5L? That higher rpm sounds like it might be a larger diameter 4.0L IAS housing with the smaller diameter 2.5L IAS sensor. This would let the extra air by resulting in the higher idle. Just a stab at it.
Your IAS housing should have 2.5L cast into it in large numbers, I've got a bunch if you need one.
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I am pretty sure it is the 2.5L one... As well as the plunger. I think it may have to do with a couple of things; one is that the throttle plate of the bored out 4.0L TB was a very tiny (visibly if you take the TB and look through it into a light) gap on the sides (gap is less than 1mm, but I think it is still letting a bit of air through). What I think this is causing is the initial high idle when I get out of the highway. Eventually, the IAS brings it back down, though.
The other thing I am suspecting is that I have a vaccum leak somewhere, because I had the same idle speed with the entire 2.5L TB when I bought the rig. By the way, the idle I am measuring by reading the RPM's from the dash, so it may be a little lower, but I doubt it, because it "feels" like what it is reading.
In any case, how much are you selling the 2.5L IAS housing for? And do you have the gasket? I may get one from you to have both TB built (that way I can temporarily replace the 4.0L to work on it and get it working right, while not being stranded without my daily driver).
Felipe
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I would ship you a IAS housing for free. It could be caused by poor machining if that much air is getting around the throttle plate. Maybe you need one of my 62mm TB's, only $85 ;)
Pictured here on the bottom:
(http://sija.org/bounty/jeepmods/DSCN6622.JPG)
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I would ship you a IAS housing for free. It could be caused by poor machining if that much air is getting around the throttle plate.
In that case, I'll take you up on the offer (I'll send you the address via PM). I checked yesterday, and the IAS housing IS the 2.5L. As for the machining, I am not sure, because at the end of the day, I am ending up with the same idle I had with the stock 2.5L TB, so that is why I am thinking more it is something else...
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It's in the mail, IAS housing and sensor. They're a little dirty on the outside, but you can deduct cleaning from the price :roflol:
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Thanks a lot, bounty... Now I am debating weather to do the mechanical work I was planning for this weekend or not because there is a Jeep activity about an hour from me that I want to go to! But I do have to get moving on checking for leaks at some point!