My understanding of the function of the wastegate is to vent the intake pressure to a pre determined value set by the calibration of the wastegate
adjustment because the turbo can produce way more boost than the engine
can handle and does not have anything to do with controling the rpm of the turbo itself which I thought was controled by the amount of exhaust gases
the car creates at any given speed/rpm. Does anybody no if this is true. Thanks

It's not exactly as you state. When the wastegate opens it allows exhaust gasses to bypass the exhaust side of the turbine. Therefore if the exhaust gasses are not going through the turbine blades it doesn't build as much boost.

The wastgate on some turbos can be adjusted so they open at a higher intake boost pressure. There are also turbo designs that do not use any wastegate control at all. In these cases the turbo system is designed so that as the turbo RPM's increase the turbo starts to loose compression efficiency and results in a maximum boost pressure.

Just increasing your boost doesn't mean you will have more power. You also have to increase the amount of fuel being injected to take advantage of the increased charge of air.

TimK

__________________
85' MB 300D Turbo
85' GMC Suburban 6.5L Diesel Turbo
2000 VW Beetle 1.9L TDI Diesel Turbo
67' Land Rover 2.5L Diesel - No turbo

So what do you do when it's so cold out your fuel gels? Smear some on toast and have another cup of coffee until it warms up outside.

Thanks for the info, so if the wastegate diaphram stops working does it fail in
the minium boost state because of the spring. I have installed a gauge in the line that goes to the ALDA unit and there is no pressure driving down the highway at 3200 rpm also verified there are no leaks in lines from banjo bolt on
back of intake through witchover valve also replaced line from housing ofturbo
to wastegate. Also I have noticed when I blow through the line that feeds the
wastegate air leaks out the back side of the wastegate. Im trying to figure out if the wastegate is the problem of no boost pressure I have also checked the safety valve on top of intake that controls the switchover valve.

I presume that you have removed the banjo bolt and cleaned it, and also cleaned the line from the bolt to the overboost protection valve, correct?

If this line is clear, please T the gauge into this line and drive the vehicle again, above 3000 rpm, with your right foot on the floor. Read the boost gauge and report back. The overboost protection valve frequently plugs and prevents the manifold pressure from reaching the ALDA.

I have cleaned the line and the banjo bolt hole put gauge in both spots but no pressure at all the line that feeds the wastegate was cracked to the point
it had to be leaking somewhere at the clamps before I tested the car at full load I blew through the new hose to the wastegate an I could feel the air come out the backside of wastegate I have not had the time yet to put a light on the backside of the wastegate to inspect it. Does the diaphragm on the wastegate usually fail in the closed state with the spring tension and if so is this a no boost state or a full boost state. I have read some threads talking about the ALDA unit has to provide the enrichment to get the boost pressure frome the turbo. Thanks for your help

The diaphragm on the wastegate is held closed by spring tension. You normally need 8-12 psi to overcome the spring, depending on the tension of the spring. If the spring is intact, then the valve is typically closed and there is no overboost protection.

However, if the spring has failed, or broken, and allows the valve to unseat, then exhaust gas simply bypasses the turbo and you don't get any boost.

The relationship between boost and ALDA is closely tied. A little boost is produced without the ALDA, which in turn begins to add fuel. The additional fuel creates more exhaust, which creates more boost, which in turn adds even more fuel, via the ALDA...................

Without some controls (wastgate, full load fuel), this process would continue until a piston melted.

So if the diaphragm fails and the spring is working normal and the seat , I should have a full boost sitituation is this correct, if so then my problem stems from the wastegate failed in a open condition that is not allowing
boost so the the system in whole is not functioning. Can I remove the wastegate to take it apart and inspect it,does it just come off after you remove the nuts. Thanks

In that sceneareo...........working wastegate........blown diaphram....you could , if the overboost protection isn't working provide somewhat more than 20 psi.....possible enough to blow a head gasket.

But open wastegate/ failed spring you will have the opposite.....no or low boost.

There are gaskets that will need replaced.......look for cracks etc....some small cracks I hear are normal.....big gaping cracks are not.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

If the diaphragm fails, you should have a full boost situation. However, I don't immediately want to confirm that the problem stems from the wastegate that has failed in an open condition. This is but one possibility. There could also be issues with the turbo itself.

I haven't personally removed the wastegate, but you would want to see if the wastegate is properly seated and the spring is holding the valve closed.
Sometimes the valve gets fouled with carbon and remains open somewhat.

interesting discussion of wastegates:
http://www.bankspower.com/Tech_howturbowastegateworks.cfm

My 87' 300DT wastegate as partially held open due to carbon build up over the 250K miles it was in service. Cleaning out the hard, almost solidly baked-on crud returned performance to normal, allowing it to spool up quickly (before that it would slowly gather acceleration, as if it was a 240D
Diesel turbo engines live by the action of their turbos, if any little thing goes wrong with them performance suffers in a big way

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

How do you tell what condition the seat is in and the state of the wastegate
without taking it off the car is it possible.

If you had a borescope maybe from the exhaust outlet side.........

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

On a 617, the turbo will still produce ~6 PSI @ 4200 rpm with the ALDA providing zero fuel enrichment (due to overboost protection, a torn ALDA diaphram, or a clogged banjo bolt). This assumes that the wastegate is functioning properly.

Here's a diagram of the turbo system.

__________________
85 300CD
83 300TD
78 240D (daughter)

Thanks for all the help im still in the troublshooting mode will inspect the leak in wastegate this weekend.