No Turbo Boost Pressure

[lakerat]

Turbo is working ,winning when engine rpm is increased but no pressure.I pluged the line that comes out of intake to swichover valve, put gauge on output of turbo that feeds wastegate input but very little pressure maybe 1 psi. If the egr valve was leaking some how could this be my trouble. Thanks

[boneheaddoctor]

Stuck wastegate will do that.............................

[lakerat]

When I blow through line that goes to wastegate air comes out bottom side of waste gate is this normal ?

[boneheaddoctor]

Originally Posted by lakerat

When I blow through line that goes to wastegate air comes out bottom side of waste gate is this normal ?

The line going to the wastegate diaphram should hold pressure....but not the end going to the inlet turbine housing......or the diaphram is ruptured if it isn't..............anke certain the hose isn't ruptured or split..........But that will not cause it to not build boost....that actually stops it making boost at a certain level determined by the spring pressure.

It lifts the wastgate open efectively bypassing the exhaust turbine.

It sounds like that wastgate is not closing or its seat has craked or broken.

[lakerat]

The spring tension should keep it closed where it does not vent into the exhaust if there was no pressure on the wastegate at all is this correct? If the egr valve was leaking somehow would this leak boost pressure. Thanks for the help.

[boneheaddoctor]

Exactly the wastegate spring holds the wastegate close therefore forcing all the exhaust to go through the turbine making bosst by spinning the turbo....the pressure line to the wastegate works to oppose that sping pressure............I.E. the sping might exert 12 lbs of pressure to hold it closed....when the boost excedes 12 psi it opens the wastegate droppping boost to 12 psi.

My understanding is the EGR rarely leaks but it might.......

How did you determine this? At idle or with a guage rigged into car on highway?

[Doktor Bert]

Originally Posted by lakerat

When I blow through line that goes to wastegate air comes out bottom side of waste gate is this normal ?

Yes...The Wastegate Valve Stem is hollow and there is a hole drilled through the side of the stem about midway down its length. This allows pressurized air acting on the diaphragm piston to 'bleed' down through the stem and cool the valve.

This bleed function also prevents 100% of the boost pressure from acting on the diaphragm.

The opening in the side of the valve stem is exposed below the diaphragm piston and there is a rectangular hole in the Wastegate Housing that allows this pressure to vent to the atmosphere.

Here is a post on the proper adjustment procedure for the wastegate. You can visually inspect the diaphragm and valve movement when you have the cover removed.

I hope you find this information helpful...Bert

Wastegate Adjustment

[pmckechnie]

Dieleldiehard ask a very important question. What model and year car are we talking about? My 91 300D has to see vacuum on the wastgate to produce boost. If the line is disconnected or pluged you get no boost. On others if the diafram is bad or the line is disconnected you will get overboost.

[dieseldiehard]

pmckechnie raised more points than I imagined
What about if the trap oxidizer is still in place? That is a bad thing when it comes to Turbo problems, esp the '87 300D and SDL
The year and model are sometimes crucial towards understanding a problem in its entirety.
I am still convinced it may be a wastegate flapper stuck open.

[Brian Carlton]

Originally Posted by Doktor Bert

Yes...The Wastegate Valve Stem is hollow and there is a hole drilled through the side of the stem about midway down its length. This allows pressurized air acting on the diaphragm piston to 'bleed' down through the stem and cool the valve.

This bleed function also prevents 100% of the boost pressure from acting on the diaphragm.

Bert,

Since many of the older vehicles have boost pressure that is below spec, is it possible that this hole becomes clogged over time and allows close to 100% boost pressure on the diaphragm?

This would cause premature opening of the valve and result in decreased maximum boost pressure.

Your thoughts on this???

[lakerat]

If the shaft has a hole down the middle of it where does this excess air go. The reason I ask is when I blow through the hose that goes to the wastegate
I feel air on the bottom of wastegate is this normal?

[Doktor Bert]

Originally Posted by Brian Carlton

Bert,

Since many of the older vehicles have boost pressure that is below spec, is it possible that this hole becomes clogged over time and allows close to 100% boost pressure on the diaphragm?

This would cause premature opening of the valve and result in decreased maximum boost pressure.

Your thoughts on this???

Your notion is correct and this is a problem on some engines. He should probably remove the cover and inspect the diaphragm visually. At that point, you can spray some WD-40 down the opening in the valve stem to verify whether it is open or not...Bert

[Brian Carlton]

Originally Posted by lakerat

Turbo is working ,winning when engine rpm is increased but no pressure.I pluged the line that comes out of intake to swichover valve, put gauge on output of turbo that feeds wastegate input but very little pressure maybe 1 psi. If the egr valve was leaking some how could this be my trouble. Thanks

Just to satisfy my curiosity, can you kindly explain exactly how you setup your boost gauge and whether you took the vehicle for a drive at high rpm's under load when checking the boost pressure.

It would be beneficial if you setup the boost gauge to tee into the line from the manifold to the overboost protection valve. You can run the gauge into the vehicle and monitor it while moving.