Topic: Weekend upgrades for my YJ & TB question

[jfrabat]

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!

[neale_rs]

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?

[oldjeep]

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.

[neale_rs]

What kind of problems could the carb cleaner cause?

[oldjeep]

What kind of problems could the carb cleaner cause?

A rather large fire

[neale_rs]

Ok, won´t be doing that!

[jfrabat]

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!

[neale_rs]

Sounds good.  I bought one a while back on ebay but haven't gotten around to putting it in.  Thanks

[jfrabat]

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.

[enginethatcould]

Does anyone know the thickness of the 4.0 TB spacer. I want to build one?

[VA_YJ]

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.

[dexetr30]

Does anyone know the thickness of the 4.0 TB spacer. I want to build one?

The ones I've seen are 1".

[enginethatcould]

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. 

[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.

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

[VA_YJ]

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.