Newbie Turbo Operation Question - bear with me

[russianwol]

Hi, I feel stupid asking this but I can't seem to find detailed enough description of how turbo works in order to answer these questions. BTW I have a 1992 W140 300SD, OM603 engine.


Does turbine simply not spin under lower RPM because the pressure of exhaust gas is not enough to turn the turbine? Or is waste gate always open and closes only when boost is needed? - this is the stupid question as what I read is that waste gate always opens when boost is too high. So what happens in low RPM/no load? Is the turbo designed to let exhaust through it without spinning at low RPM?


Another question.
There are 2 pressure lines that feed into a air pressure sensor. One comes out of intake manifold and can be called a boost pressure. The other is coming out of ALDA but they are joined together by a "Connection" with "Restriction" on the ALDA side connector. Anyone knows why?

In oder to install boost gague - would I tap into the ALDA line, Intake Manifold Line or line that goes to the sensor? Or should I have 3 gauges to get a better read?


What is the purpose of the "air flow sensor potentiometer"? It's a flap thingy in the air intake, pass the filter in a weird compartment that also has the air flow/temperature sensor. I mean there's a gate that looks like is spring loaded. Does the gate open by a way of some actuator or by simply force of air sucked in by turbo? Does the potentiometer report the "air mass" to EDS based on how wide the flap open?

There is a vacuum line called "a" - fresh air to passenger compartment. I don't get this. How is that line delivering fresh air if it's a vacuum line? Or does it simply control some sort of transducer? In my case it's not connected to anything which worries me.

Please see pictures for reference.

[Putty]

that line that tees with your alda goes to your tranny modulator...its a supply line for shifting.

Your turbocharger is constantly turning when the engine is on however, just like propellers on airplanes, a particular turbo can only boost so much and the whine of a turbo is also dependant on how hard your engine is expelling its exhaust and how fast your engine is turning.

ever notice how loud your turbo gets when going up a hill?

right around 2200 RPM is my sweet spot on boost...when a turbo gets to a certain RPM, it starts creating the pressures that make an impact on performance...and you start to feel it.

The wastegate is somewhat or a gray area for me...ask Brian Carlton.

Make sure that the line from your intake manifold is not clogged...EGR's have a tendency to clog them drastically hindering performance.

Thats all I think I got

[Cervan]

Originally Posted by russianwol

Hi, I feel stupid asking this but I can't seem to find detailed enough description of how turbo works in order to answer these questions. BTW I have a 1992 W140 300SD, OM603 engine.


Does turbine simply not spin under lower RPM because the pressure of exhaust gas is not enough to turn the turbine? Or is waste gate always open and closes only when boost is needed? - this is the stupid question as what I read is that waste gate always opens when boost is too high. So what happens in low RPM/no load? Is the turbo designed to let exhaust through it without spinning at low RPM?


Another question.
There are 2 pressure lines that feed into a air pressure sensor. One comes out of intake manifold and can be called a boost pressure. The other is coming out of ALDA but they are joined together by a "Connection" with "Restriction" on the ALDA side connector. Anyone knows why?

In oder to install boost gague - would I tap into the ALDA line, Intake Manifold Line or line that goes to the sensor? Or should I have 3 gauges to get a better read?


What is the purpose of the "air flow sensor potentiometer"? It's a flap thingy in the air intake, pass the filter in a weird compartment that also has the air flow/temperature sensor. I mean there's a gate that looks like is spring loaded. Does the gate open by a way of some actuator or by simply force of air sucked in by turbo? Does the potentiometer report the "air mass" to EDS based on how wide the flap open?

There is a vacuum line called "a" - fresh air to passenger compartment. I don't get this. How is that line delivering fresh air if it's a vacuum line? Or does it simply control some sort of transducer? In my case it's not connected to anything which worries me.

Please see pictures for reference.

The wastegate is allways closed, it opens when a certain boost pressure is met, and it keep the turbo from generating more boost.

The alda is a baromotere that meters how much fuel is injected into the engine before boost comes up, (otherwise you will get black smoke when you floor it) and the other sensor is the boost protection valve, so if your wastegate fails your engine doesnt melt.

[blackestate]

The reason that you get no boost at low RPM is because the gas flow in the exhuast is not a lot greater that the intake, so the turbo is spinning all of the time, just at idle it is not compressing any air.
When you are at high power, there is more air pushing the exhaust turbine, which increases the speed, and generates pressure in the intake that is greater than atmosphere.
Over simplified, but you get the idea.
The waste gate opens at a set level, to try and prevent overboost. A condition of too much pressure causing issues, like blown head gaskets.
I believe the box that the hoses run to is to tell the ALDA to add more fuel, as there is boost (more air +more fuel= more go power)

If I were to install a boost gauge, I would mount it right at the intake manifold, not splice into one of these lines.

[russianwol]

Thanks for replies! I'm still learning. The problem I'm trying to troubleshoot is that I stop getting boost after car warms up. So I only get like 2 enjoyable minutes of driving. After that acceleration is very sluggish. I don't hear any noise except the high revving motor And it's probably killing my diesel mileage.

Here is a follow up pic on the Air Flow Potentiometer for those who are interested.

And another pic with a potential location to install boost gauge on the manifold. Looks like the hole is predrilled and just capped. How do I find correct nipple for the thread? Do I just figure out the threading and diameter size and buy the part online?

How do I find out if the waste gate is stuck open after the car warms up? Should I put a vacuum gauge on my waste gate vacuum line to the waste gate actuator?

[russianwol]

Originally Posted by blackestate

condition of too much pressure causing issues, like blown head gaskets.
I believe the box that the hoses run to is to tell the ALDA to add more fuel, as there is boost (more air +more fuel= more go power)

Did you mean to say "tell the IP to add more fuel"?

[BoomInTheTrunk]

Most of the people have told you what the wastegate is for and why its there but not when its used. can you here that wastegate when the transmission shifts to a taller gear, you should. When the car is about to shift the waste gate opens allowing the pressure to relieve. You wouldn't want to have pressure when the engine is at lower RPMS because then you would have to much air then the engine would want, so the waste gate opens and relieves the pressure.

[russianwol]

So that means that If I do hook up vacuum gauge to that line I should see different vacuum right before shifting?

[BoomInTheTrunk]

Originally Posted by russianwol

So that means that If I do hook up vacuum gauge to that line I should see different vacuum right before shifting?

well i dont own a turbo but i do know what a waste gate does and what it is for. I believe the waste gate opens once it reaches a certain amount of vacuum or boost like most do.

[russianwol]

Well you mentioned an interesting issue that I have not though/read about before. Does the the computer actually open waste gate before it's going to shift? Or is it going to shift when the boost reaches max? Or does it not matter to the motor what the transmission is doing?

Side question? In a W140 what' the best way to run lines from engine compartment to inside? Looking from above the engine I don't see any obvious entry points to snake the lines through the firewall. Is there something underneath that I can see? I noticed there's some sort of a plug behind the accelerator pedal that looks like it can open a hole to the "outside". I have yet to figure out a way to find info about this hole in the Star Manual.

[sixto]

Your car has a backwards wastegate. A vacuum device closes the wastegate when the ECU deems you worthy of acceleration. You can try to sort out all the parameters the ECU considers or you can cut to the chase and replace the the vacuum actuator with a proper boost actuator. gsxr's thread has the best information on this topic.

IIRC, there is a line from the manifold to the a MAP sensor (Denso or Nippondenso brand) on the firewall with a branch to the ALDA. There is never a vacuum in this line so there's no connection to the transmission (or maybe I misread earlier posts). If you go with a boost wastegate controller, this MAP sensor is not needed, but you don't have an overboost protection mechanism. You can retrofit the overboost system from a 603.96 or 603.970 if you want. A 617 system might work as well.

The MAF sensor helps the ECU decide how to regulate EGR and boost. I think the ECU is smart enough to rationalize airflow when the EGR valve should be open and cut boost if it thinks something's wrong; i.e., the EGR system isn't funcitoning properly.

My 93 SD wasn't boosting when I first got it. One of my early mods was to provide a constant vacuum signal to the wastegate actuator. As long as you don't hold the pedal to the floor, you will never have more boost than the engine can handle. If you find yourself holding the pedal to the floor frequently, trade your car for an S500. But I digress, the next mod was to adapt a boost actuator for the wastegate.

I prefer to tap a boost gauge to the ALDA line so I know if/when the overboost circuit is in effect. Since your car doesn't effect overboost protection by cutting the signal to the ALDA, tapping a boost gauge upstream or downstream of the MAP sensor should give you the same reading.

Sixto
87 300D

[russianwol]

Thanks sixto. BTW where would I otherwise find this information about backwards waste gate? The Star Manual doesn't seem to describe things, just provide diagrams. Hmm maybe that's why MB Mechanics charge what they charge

[russianwol]

In my system would an EGR valve cut vacuum out of the waste gate actuator line to get it to open and thus cut the boost?

I think I'm going to find out how to hook up monitoring to EDS(ECU) and find out what are all the signals that all the sensors are sending. I think Star Manual might have the correct values. I have a feeling that the air temp sensor might be reporting incorrectly or perhaps the air mass could be a problem.

So the pressure from ALDA and intake manifold would generally be the same and that's why they are connected? I wonder what is the function of the "Restriction" in that connector?

And also, is my previous post with a picture where to put in boost valve correct? Or should I just put a boost gauge after the connection of lines from manifold and ALDA?

Is "ARF" and "EGR" same terms?

BTW Here is a pic of EDS from Start Manual FWIW

[russianwol]

Oh another thing - I have a manual vacuum pump. Should I try to hook it up to the waste gate actuator and operate it manually? Of course I want to measure the vacuum that is put on that line when I get boost and when I don't get boost.

[sixto]

By all means, use the manual pump to ensure the wastegate closes under vacuum. Then rather than or in addition to a boost gauge, run a vaccum gauge to the cabin so you can monitor wastegate actuation under various vacuum conditions.

There should be sufficient vacuum for all users. Applying vacuum to the EGR actuator shouldn't starve the boost actuator.

Sixto
87 300D