Cable drive TB Hanging open.

[Redtruck-VA]

This problem is ******* me off and is really making no sense to me.
I have a new LSX90mm cable drive TB on Redtruck, needed for the Megasquirt install. The problem is the new LSX90mm TB hangs open at a high idle. I can snap it and it usually will close. I set the TB up on the bench and it works flawlessly with just the factory installed return spring. Even when installed on the truck with the engine off, it works as it should. Start the engine and pull the rpm's up to say 2000rpm and release the throttle and it hangs at around 1200rpm, snap the throttle and it will close, sometimes. I have two carburetor return springs on it and it closes. I can actually see the blade is slightly open when it is hung open. My question is: Is this a common characteristic of a large single blade TB? Obviously the accelerator pedal pressure is too high to be comfortably driven.

 

[MegaMouseGW]

Hmm this does sound like the airflow pressure is the problem. Some things you can check out:

Check your throttle cable and make sure there are no tight bends in it causing unwanted binding.

Check to be sure that there is no unnecessary slack in the throttle cable where it comes out of the jacket.

Before you installed the new TB did you be sure it was working as free as possible with all the parts needed installed on it??

Worse comes to worse spray the linkage where it goes into the TB with a good penetrating lubricant. A silicon based one would be best.

Even though I believe that this sounds lie too much air pressure it is always good to check other things out also. Lets us know what you find.

 

[Redtruck-VA]

I've done all that and ran it with the drive cable disconnected. Still hangs.....

 

[MegaMouseGW]

Ok try this if you feel you can do it:

Remove the TB, then remove the TB butterfly valve plate and look inside the TB to see if there are scuff marks where the plate might be rubbing. If you find any scuff or wear marks you can try to reinstall the plate making sure it is centered, or using some sandpaper shave down the side of the plate that is rubbing. Shaving down the plate should only be done as a last result though.

 

[Redtruck-VA]

Yep, I took it off and went through the whole thing on the bench, checking for any kind of binding or friction. This NOT a quality throttle body but it works completely smooth except when the engine is running. I personally have never messed with a TB of this size. The original 85mm FBW TB closes like a guillotine and this one doesn't have as much tension. Anyone with any experience using a cable drive TB?

 

[MegaMouseGW]

Mine is Cable Driven and to tell the truth I have never had any problems. But it is a BBK unit and their TB's are very high quality.

 

[Redtruck-VA]

What size is the TB and do you use a return spring? If so, approximately how strong is it?
I had forgotten the V10's use cable drive. Or a more accurate statement is I didn't know V10 used cable drive.

Thanks,

 

[MegaMouseGW]

Here is the link to the exact one I have on my truck: BBK : 2003-2007 Dodge Viper Twin 67mm BBK Power Plus Throttle Body[]=1457

Had to use the info from the Viper that the motor came out of to get it right. Not real sure on how strong the spring is because it was on the TB when I bought it.
And yup the Vipers had the cable actuated TB instead of the drive by wire like some of the SRT10 trucks.

 

[Redtruck-VA]

Here is the link to the exact one I have on my truck: BBK : 2003-2007 Dodge Viper Twin 67mm BBK Power Plus Throttle Body[]=1457

Had to use the info from the Viper that the motor came out of to get it right. Not real sure on how strong the spring is because it was on the TB when I bought it.
And yup the Vipers had the cable actuated TB instead of the drive by wire like some of the SRT10 trucks.

Twin 67mm, this is the point I'm thinking is maybe important. My thought being the smaller twin blades may not develop the frontal defection that the single 90mm blade creates. A 90mm blade may simply be too large. ??? Thoughts on this is invited...

 

[MegaMouseGW]

Ok look at the area that yours displaces. It displaces 6361mm.
Now look at what mine displaces: My BBK unit displaces 3525mm each side or 7050mm.

Ok that is the area of displacement total for both mine and yours. Mine is displacing a little under 700mm total. That is a rather large difference.
Looking at what you said mine has more area to deflect but it is between 2 blades instead of 1. You may be on the right track with yours just a bit too big. But again you did state that it was not a quality part. That might be the problem. The quality of the part might be what is causing the problem.

Here is the largest that BBK offers: BBK : 05-12 Dodge Hemi 5.7L / 6.1L 85mm Power Plus Throttle Body[]=797&car_motor_key[]=1633

Now it is drive by wire though which would not suit your application. Lemme do a bit more research for you and maybe I can find a unit that will work without problems.

 

[Redtruck-VA]

What throws a wrench into my theory is that the LS folks use an even bigger 102mm. Which makes me wonder how they are solving the problem. I'm using LS(X) TB and sensors with the Megasquirt. Maybe a push/pull throttle is needed?

 

[MegaMouseGW]

Ok looking for another TB for you I found something interesting. When you reinstalled the Throttle Position Sensor, did you make sure it was on right?? This might be the problem but I am not sure. Was looking at a video of the install of a new TB on a hemi and they stated that the TPS if not installed properly can cause binding.

 

[Redtruck-VA]

Ok looking for another TB for you I found something interesting. When you reinstalled the Throttle Position Sensor, did you make sure it was on right?? This might be the problem but I am not sure. Was looking at a video of the install of a new TB on a hemi and they stated that the TPS if not installed properly can cause binding.

Like I said the TB works smooth and clean as long as the engine is not running. When air is being pulled then the TB hangs a little.

 

[MegaMouseGW]

Ok I am stumped now. Went through all I know on the subject maybe someone else will chime in.

 

[PCA4208]

Why don't you find a stock ls throttle body and see if that works. It may be a longshot, but who knows.

 

[Redtruck-VA]

Why don't you find a stock ls throttle body and see if that works. It may be a longshot, but who knows.

That may be a way to go, they are relatively cheap. Just has a feel of going backwards... at this point.

 

[Redtruck-VA]

Update: this is an indicator how things have been going for me lately. I've been fighting this hanging throttle issue for well over a week and finally gave up and put two springs on it so I could get on with tuning. Well this morning I went out and was going to start from scratch testing it. The TB worked as it should using the heavier of the two springs. Go figure..... magic right?

 

[MegaMouseGW]

Update: this is an indicator how things have been going for me lately. I've been fighting this hanging throttle issue for well over a week and finally gave up and put two springs on it so I could get on with tuning. Well this morning I went out and was going to start from scratch testing it. The TB worked as it should using the heavier of the two springs. Go figure..... magic right?

Sounds like you got a visit from the great fairy of tuning.

 

[Redtruck-VA]

Sounds like you got a visit from the great fairy of tuning.

I'm old and don't like magic or fairies...

I keep going back to basic's trying to nail the idle down solid. Needless to say I ain't got it nailed yet.
I've got it were it over runs about three times before it is settled.

 

[MegaMouseGW]

Ok something else to try and I only thought about this while going down the road to the store:

Do this ONLY if you feel you have the skills to do it.
Remove the TB from your truck and take it to a bench.
Dissasemble the throttle body until you can get the butterfly shaft out of the unit.
As you are removing the shaft be aware of ANY spots that seem a bit difficult when pulling it out.
Look at the shaft and look for wear spots, pay particular attention for excessive wear.
Place the shaft on a flat piece of glass, and then slowly raise one side of the glass allowing the shaft to roll. If it stops or sides then it is bent. A bent butterfly shaft can cause the problems you describe and may be just what you are experiencing.