Wastegate trouble shooting

[jsveb]

First a little background information:

About six months ago I picked up my car in Campbell from Dell Autobody. After an eleven month post rear-end accident repair job, it was finally time to pick up the car.

I only drove the car--because I was in the middle of a trans-Atlantic move--from the shop plus a small backroad drive.

Fast fwd...about a week ago I wanted to dilute that California gas with some non-ethanol European gas. As I drove back I decided to massage the wastegate. It scared me sheitless; the WG didn't open??? I bought this wastegate from Cole maybe three years ago. It has a 0.8bar spring and has worked flawless since installed. However, since the car had been sitting I decided to removed and inspect the WG. The diaphragm was slightly pinched, but I could not find anything wrong with it as such. In spite of this I decided to install my spare 0.6 bar WG. Tonight I finally had a chance to test it. Guess what, it still doesn't open.
I also tested this WG before installation, and it works flawless. Opened somewhere between 0.4-0.6 bar.

Rant: I am getting so tired of all the crap I discover that the shops working on the car did not do properly. I won't get into this more as it a sad story. I just can't help wonder why the MBC was fully opened six months ago when I picked it up??.

I have done the preliminary checks of the the WG circuit., supported by relevant PP threads. Everything seems to be connected properly in the engine bay and on the WG itself.

I have only done low speed and very short boosts, so I don't know if the car will truly hold boost, but it runs and idles just fine with no indication of any leaks whatsoever.

Question 1: will the car be able to build boost seemingly normal with a leak as a result of improper WG hook-up?

The MBC does (open or closed) does not seems to work. It used to be hooked up, but I have NEVER,not even once opened it up.

Question 2: What could be wrong? I am extremely limited on time and need to get the car through a very strict DOT-type inspection before I can legally drive it, outside of Mexico.

Any and all help is appreciated.

[Ronnie's.930]

Jesper, just to verify - the top spout on the wastegate is a vent to atmosphere and the side spout is where the boost signal hose connects; is that how yours is hooked up?

1) - It would build boost as normal, but there should be a major rich misfire with a leak like you describe. In other words, when the WUR went into full throttle enrichment mode, the engine would stumble horribly due to being too rich (the air leak would make the fuel metering arm travel down farther than the actual fuel need requires).

2) - If the wastgate is in sound condition like you said, then you must have a hose connected incorrectly and/or one of them is pinched or the signal hose is damaged in some way and not sealing or not allowing air to get through (plugged with something, collapsed internally, etc.). Or maybe the spout on the intercooler where the wastegate signal hose connects is damaged in some way?

[jsveb]

Originally Posted by Ronnie's.930

Jesper, just to verify - the top spout on the wastegate is a vent to atmosphere and the side spout is where the boost signal hose connects; is that how yours is hooked up?

1) - It would build boost as normal, but there should be a major rich misfire with a leak like you describe. In other words, when the WUR went into full throttle enrichment mode, the engine would stumble horribly due to being too rich (the air leak would make the fuel metering arm travel down farther than the actual fuel need requires).

2) - If the wastgate is in sound condition like you said, then you must have a hose connected incorrectly and/or one of them is pinched or the signal hose is damaged in some way and not sealing or not allowing air to get through (plugged with something, collapsed internally, etc.).

Thanks Ronnie!

Yes, it is hooked up as you describe. Except for the vent is not vented. It is routed through the MBC.

I am considering plugging that hose and just try and vent the WG in order to bypass the MBC, and simply check the WG itself.

[jsveb]

I stole this picture:

From this thread:
manual boost controller take 2


This is how it is, or used to be hooked up.
is there any way the MBC itself can be messed up?

[Ronnie's.930]

That sounds like a plan - take the MBC out of the equation and see if the wastgate operates normally then.

One thing I wanted to add is my "rich misfire" jibber jabber is not guaranteed to take place, as depending on the turbocharger you have (how quickly it builds boost) the system will overboost very quickly - way before you would notice a misfire like I described. I know this from experience, when like a complete dumbass, I once left the signal hose disconnected from the intercooler by accident, and the thing overboosted within a second or two of me flooring the accelerator.

[Ronnie's.930]

If the MBC's rubber diaphragm is torn, a lot of air will leak out of its bleed hole and not as much pressure would make it to the wastgate.

[jsveb]

The engine seems to run fine.

Beware these tests are done on secluded, and windy, roads so single pilot read-outs are not as precise as I wish. However, AFRs are in the low 14s in second gear back road moderate driving. Dropping down to mid 11s-ish as boost builds. I let off at 1.0 bar.

The is no bogging or rich condition detected.

Bedtime here in Denmark.

Thanks again.

[fasteddie313]

In my experience with the 930 WG, the TOP port is the one to check for leaks. You should be able to suck a vacuum on it, put your tongue over the line, and it remain under vacuum. If it does not your diaphragm is bad or your top port line is bad, something is leaking that shouldn't.
The bottom port not so much because there is some leakage past the valve stem from the exhaust piping area so it won't hold a vacuum like the well sealed top port always should.

The boost/vac reference line from the intake manifold to the bottom/side port of the WG plumbs pressure under the spring and when the pressure overcomes the spring the WG opens your exhaust to the dump pipe. It is like a piston in there but instead of rings to seal it has a diaphragm.

In that pic of a top port actuator MBC, to remove it you would want the line going to the WG top port unplugged, vented to atmosphere. This is meant to plumb adjustable positive pressure to the top port, which is the sprung side pushing down, in an effort to help the spring hold the WG shut to help the spring fight against more bottom port pressure trying to open the WG so it takes more boost in the bottom port of the WG to get it to open, thus increasing your boost setting.

The other line that goes to the bottom port and T's to the MBC needs to have the T'd off hose plugged because if it is not the this is a massive leak in your WG bottom port intake pressure reference line, with that T'd off hose not plugged your WG will not open and you will overboost quickly.

If your MBC is for some reason leaking pressure out of the bottom WG port line then full boost will not reach the bottom WG port to open it and you will overboost, so yes the MBC malfunctioning could cause overboost as you describe..

[mark houghton]

Originally Posted by fasteddie313

In my experience with the 930 WG, the TOP port is the one to check for leaks. You should be able to suck a vacuum on it, put your tongue over the line, and it remain under vacuum. If it does not your diaphragm is bad or your top port line is bad, something is leaking that shouldn't.
The bottom port not so much because there is some leakage past the valve stem from the exhaust piping area so it won't hold a vacuum like the well sealed top port always should.

The boost/vac reference line from the intake manifold to the bottom/side port of the WG plumbs pressure under the spring and when the pressure overcomes the spring the WG opens your exhaust to the dump pipe. It is like a piston in there but instead of rings to seal it has a diaphragm.

In that pic of a top port actuator MBC, to remove it you would want the line going to the WG top port unplugged, vented to atmosphere. This is meant to plumb adjustable positive pressure to the top port, which is the sprung side pushing down, in an effort to help the spring hold the WG shut to help the spring fight against more bottom port pressure trying to open the WG so it takes more boost in the bottom port of the WG to get it to open, thus increasing your boost setting.

The other line that goes to the bottom port and T's to the MBC needs to have the T'd off hose plugged because if it is not the this is a massive leak in your WG bottom port intake pressure reference line, with that T'd off hose not plugged your WG will not open and you will overboost quickly.

If your MBC is for some reason leaking pressure out of the bottom WG port line then full boost will not reach the bottom WG port to open it and you will overboost, so yes the MBC malfunctioning could cause overboost as you describe..

+1. Great description and advice.

[DSPTurtle]

Did you pull the line off the vent fitting on the top? As long as it's not raining or going through puddles, a quick test drive with that port removed will be fine. With nothing connected to the vent on the top, the only thing working is the spring in the WG. Quick easy test. Even easier if you have access to a regulated airflow you can blow into the signal hose and see what is going on without jeapordizing your motor. Unplug from the intercooler and blow into the line with 10-15 psi and you should hear the valve click as it opens and closes.

[JakobM]

It is very simple:

If the WG is ok internally and do not open, then you have SAME pressure above and under the internal membrane WG valve, meaning no bleeding of air gets to WG, meaning no valve motion, meaning all exhaust gas goes to turbine, meaning +2 bar instantly and most likely detonation

Pull the top hose off and your WG then WILL open accordingly to your spring ratio. If it still do not open you have a mechanical issue inside the WG

The way to test your WG is to attached compressed air to the lower hose, pull the top hose, read the guage on the "air-gun" till it reach spring ratio and see the wg-valve open by visual looking through the exhaust outlet hole

[jsveb]

Thanks guys.

I have zero time in the garage these days. Might be another month unless I can sneak out there tomorrow.

The wastegate currently installed is tested and works fine. I need to dig into the MBC etc.

[jsveb]

Back at it.

Pulled the "vent side" from the mbc off the wg.

Now the wg opens just fine. I have a 0.4 bar spring I believe, but the wg opens at about 0.3-0.35 read on the 935-style gauge.

I wonder what the shop did to mess up the mbc??

[WinRice]

Your MBC is nothing more than a pressure regulator like what's on a garage air compressor. The way it's plumbed in the diagram above it's applying boost pressure to the top of the WG, making the pressure the same on both sides of the WG diaphragm so the WG doesn't open. Once boost rises to the set pressure of the MBC it opens and bleeds off pressure to the top of the WG and allows the WG to open.

As others have mentioned, the MBC has a spring and diaphragm that boost pressure acts against to open the internal valve. Several items can cause the problem:

1. Bad adjustment. On most of these things you have to pull up on the knob until you hear and feel a click, then the knob rotates. Turning the knob clockwise increases the spring tension, and the boost pressure.

2. Bad diaphragm. Leaks the boost pressure so the valve never opens to bleed off pressure.

3. Bad spring. Spring corroded and broke jamming the valve. Very rare but it happens.

4. Valve is corroded and stuck.

5. MBC is plumbed incorrectly so the diaphragm never sees the boost pressure, and never opens.

If you have an air compressor, you can test the MBC. Pull the MBC out of the car. Dial the regulator on your compressor to '0'. Attached the compressor hose to the MBC boost inlet port (make sure it's the correct port). Dial up your compressor regulator slowly until the MBC releases pressure. Make note of the pressure, lack of release or any air leaks.

[jsveb]

Thanks, winrice

I believe I understand the functions of wg and mbc.

The wg works fine. I don't know about the mbc, but for now it is out of the loop.

I just don't understand why the shop would mess with the plumbing and or the mbc.