Air Leak!

Notches, fastbacks, squarebacks.

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Max Welton
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Air Leak!

Post by Max Welton » Tue Feb 24, 2015 9:57 pm

I'm having trouble with an air leak in my throttle-body. With the AAR blocked-off and the idle adjustment all the way in, it's still passing enough air to "idle" at 1800 rpms. Putting my hand over the inlet does choke it off. Using my finger I can reduce RPMs a bit by covering the regular idle inlet (lower left in the picture) but also by covering the area on either side where the throttle shaft goes through the body on either side. Any ideas on how to get this TB to seal up?

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Max

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Piledriver
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Re: Air Leak!

Post by Piledriver » Wed Feb 25, 2015 3:32 am

Bush the shaft bores most likely, based on your description.
Its also possible the butterfly is not centered absolutely perfectly from the picture: it must be.

If memory serves the adjuster on those almost fully seals when screwed in all the way, so if the butterfly//stop is letting it close properly,and the butterfly/surrounding bore is not horribly worn, it doesn't leave much. At least they don't wear like Automatic Vanagon TBs, with a 3 foot long 2 pound steel linkage bar from the trans driving the butterfly into the bore.(idiot designed)

Are you using the factory warm up fast idle valve?
What's your idle timing?

I have a T3 plenum I can dig out in the morning to see if it jogs any more brain cells.
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Re: Air Leak!

Post by Max Welton » Wed Feb 25, 2015 10:50 pm

I was using the AAR, but the last thing I need right now is more air. It's currently plugged. ;-)

I've got the idle down to 1350 rpms. Advance at that engine speed is 17. It will be 12 at 900 once I stem the flow. That's what I had before the rebuild, but that was with a different cam and lower CR.

This TB is actually composed of parts from two different assemblies. The butterfly and shaft are from one and the body is from another.

Max

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Re: Air Leak!

Post by Piledriver » Thu Feb 26, 2015 12:00 am

Try not to use the main timing/VE maps to set up idle, there are a herd of idle control features that work better.

Use your idle timing/idle advance and idle VE features so it drops to 12 or so at idle.
RPM may come right down.

Hmmm... You will have to fix your TPS so it "knows" its idling, could be the whole problem.

I also use the cold timing feature to for extra cold temp advance, and to pull 10 degrees of timing from ~80F to 160F to help it warm up faster.

Fuel cut should also kick fuel back in just above idle target RPM.

Sometimes I think MS3 has too many idle settings, as several interact... my only real complaint is they are not all visible/tunable on the same page in TS, but massaged right they all work together well.
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Re: Air Leak!

Post by Max Welton » Thu Feb 26, 2015 1:31 am

Before the rebuild (and before I shuffled the TB components) idle was well settled. One key was making a four cell square around the desired MAP/RPM idle point flat on both the timing and VE tables. If advance increases between 800 and 1000 rpms it can get into a cycle where the MAP/RPM point moves in a circular pattern as fuel and ignition react to the changes in MAP and RPMs. Needs to be flat there for a stable idle. I still have that configuration. There is now just too much air getting in.

But I actually do use cold advance feature to help give a little RPM boost below a certain CLT. Got the idea from a friend who had an in-cabin timing control hooked to his fancy distributor. He was using it to dial-in a cold idle by adding a little advance until the engine built a little heat. I just made it automatic.

Actually another change I made was to move the CLT sensor from the oil galley in the 3/4 head to the area just behind the thermostat under the 1/2 head. I needed to adjust the WUE to account for the much lower operating range. That's one of the things I did today to get the idle down to the 1300-1400 rpm range.

I am only using the TPS to make my logs more readable. Nothing to do with the idle. I'm using MAPdot to drive the acceleration enrichment.

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Re: Air Leak!

Post by Piledriver » Thu Feb 26, 2015 9:16 pm

If setting your idle up like an MS1 works for you, good.
I simply suspect you could make it work a lot better using it like an MS3.

Just noting that a great many of the MS3 code changes/feature additions over the last 2 years have been idle related.
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Re: Air Leak!

Post by Max Welton » Fri Mar 06, 2015 7:04 pm

So I've done some asking around and it seems nobody is set up to rebush type-3 TBs. With so few out there I guess it doesn't make economic sense. So I've got a nutty idea and two nice days in front of me.

I'm also setting up a 2110 using TBs from a Honda VFR800 motorcycle. They are very nicely made and seal up wonderfully. They even held solvent for quite a while in the parts-washing sink. One thing Honda did was apply a smear of some sort of rubbery stuff the to the inside of the bore when the butterfly rests. You can just see it in this picture.

Image

So my nutty idea is to try to replicate this with a smear of RTV. But I need to keep it from adhering to the butterfly plate while still taking the edge shape. What will RTV not stick to? Maybe a smear of wax on the edge of the butterfly? Could I coat the shaft with the same non-stick stuff and use RTV to fill the space between the shaft and the bore in the TB to create an air-seal?

Max

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Re: Air Leak!

Post by Steve Arndt » Fri Mar 06, 2015 7:31 pm

17 at idle is a bunch, especially if you added more compression to the combo. I like 10 to 12 at hot idle on my injected squishy engine.

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Re: Air Leak!

Post by Max Welton » Fri Mar 06, 2015 7:44 pm

Steve, it's only 17 because "idle" is currently 1300-1400 rpms. At 900 rpms it is 12 degrees.

What is your timing at 1400 rpms?

Max

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Re: Air Leak!

Post by Piledriver » Sat Mar 07, 2015 3:00 am

Use the idle timing and idle VE tables and it will drop to whatever you set it to be at idle, when idle mode is activated.
(TPS is usually the controller, but a switch will work, maybe better)

There is no need to set an idle area up in the main tables---you have an MS3.(even Ms2E has ~reasonable idle features)

I had a hosed Automatic Vanagon TB, the shaft play was fine but the butterfly rubbing on the bore was the thrust surface for a ~3' long steel bar off the trans governor bellcrank. (vertical shaft orientation, no vacuum governor, uses throttle position like a Golf automatic etc)

I sanded the worn areas for fresh metal, and filled it all with JBweld, covered with tape to keep the shape close and the epoxy in place, finished up with some light sanding on the spots that hit.
Worked fine, still using it (I think.)
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Max Welton
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Re: Air Leak!

Post by Max Welton » Sat Mar 07, 2015 11:42 am

The MS3 is on the 2110. For this engine I'm using MS2-Extra. I don't have an idle valve other than the original type-3 AAR which is currently blocked off.

I do have a very real problem with extra air finding its way into the TB past the shaft and butterfly. My sense is that I need to get this under control whether I use the MS idle control features or not.

But fine. I like an experiment. Remember : MS2ex and no idle control valve and an unresolved air leak.

With no idle control valve nothing under Startup/Idle => Idle Control can be used.

Under Idle Advance Settings I find the Closed Loop idle target curve as a function of CLT. To begin I'm dialing in 950 rpms (warmed up).

Under Idle Advance Settings I'll set Idle advance on: Adaptive and Apply as Adder because I want to use closed-loop control. The problem here is that when I select CL PID all the other criteria go away. When does Idle Advance control engage?

So I set "condition is:" to manual and can now specify TPS, RPM, load, CLT criteria and a delay.

The next problem is the RPM criteria. The default is 1000 RPMs. In order to get idle advance control to engage (with the TB air leak unresolved) I will have to set this to something like 1400 rpms.


So now do you see why I want to deal with the air leak first??

Max

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Re: Air Leak!

Post by Piledriver » Sat Mar 07, 2015 6:27 pm

Gotcha, an ljet throttle switch would work well with a pullup and limiting resistor.
Thought: Might be easier to get an LJet TB, cut back the djet TB area and graft it on.
It has a tapered sealing surface that originally used a rubber gasket.

OTOH I have a good T3 manifold setup I need to find a home for cheap.
The fellow that bought the T3 cooling system didn't want it or the OG uncut case or newish heads.
I'll check the bushings out but it was working fine, and wasn't driven much.
(The CIS got filled with water due to a broken vent tube at the fuel filler acting like a funnel)

PM if you need it.
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Re: Air Leak!

Post by Max Welton » Sat Mar 07, 2015 7:29 pm

No problem.

So I did a little testing to see if there was something RTV would not stick to. What I want to do is coat the inside of the throttle bores with RTV and the outside of the throttle shaft with something the RTV doesn't adhere to. Then let the RTV fill the gap.

After trying Carnuba car wax, PAM non-stick cooking spray and some disk brake bearing grease the surprise winner is ... Chapstick! The RTV I'm using is the High-temp red Permatex. Apparently RTV also doesn't stick to a 1997 Volvo 850 turbo sunroof rubber trim, but that isn't very helpful.

I tried one bore on one of several old type-3 TBs and the shaft now fits the bore perfectly and moves smoothly. So I just did the TB I'm using in the car. In a few hours I will know how it turned out. Then I can try the technique on the stock idle screw head and around the butterfly.

Max

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Re: Air Leak!

Post by Piledriver » Sat Mar 07, 2015 7:40 pm

Not thrilled with the idea how RTV will wear on a throttle shaft, but it or JBWeld would surely secure some brass or self-lubricating plastic bushings, resulting in a self aligning setup during cure.

Chapstick as mold release---great tip!
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Re: Air Leak!

Post by Max Welton » Sun Mar 08, 2015 7:11 pm

Point taken. The only way I'll know how well it does over time is to run it and let some time pass.

Meanwhile, it's working really well. After doing the throttle bores, the idle screw tip and the butterfly plate to throttle bore interface the amount of leakage is small enough to make the stock idle screw usable again. The throttle feels nice and it closes consistently.

I let it idle for ~30 minutes in the barn and finally arrived at an idle of ~1000 rpms with the stock high-idle valve (AAR) connected and partly closed. I know that this AAR does not close off completely on the bench so the total idle airflow will always be the combination of the AAR leakage and the idle screw. So the current setting should be good enough for tomorrow morning and I'm carrying a 15mm closed end and a screwdriver to make adjustments as necessary.

Here is a before and after looking down the throat with a light behind. Big difference.

Image

Image

Max

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