[makke]

Not getting much traction at 1Addicts. Thought I would try the e90 sister forums...

I have recently installed an UltraGauge (http://www.ultra-gauge.com/ultragauge/) to keep an eye on my 2012 135i with 50K miles on the clock. One thing has jumped out at me that I don't understand. I am only getting boost when at WOT or close to it. With smaller throttle inputs, I get no boost regardless of engine RPM. Here is an example:

https://photos.app.goo.gl/VfQNbiWUTN32zTBG7

At 3,400 RPM, Boost PSI is showing -0.58ish which, I believe, is nominal vacuum in the intake. I can rev it up all the way to the 7K red-line and still have zero boost if I do it without large throttle input. The only way I can get boost (up to about 10 psi) is by stomping on the gas pedal...

Is this normal behavior? If so, how the heck is this accomplished?

To my understanding, there are two methods of controlling boost built into the system. Method 1 is via the wastegate valve on the exhaust side of the turbo and method 2 is via the diverter valve on the intake side. Looking at the latter first, here is BMW's description of the diverter valve in ST916:

The basic function of the diverter valve remains the same. The difference compared to the N54 engine is that the diverter valve is not operated pneumatically. The diverter valve on the N55 engine is an electric actuator that is controlled directly by the DME. The number of components has been greatly reduced by positioning the diverter valve on the turbocharger compressor housing.

The diverter valve is designed to release unwanted pressure in the intake by connecting the pressure side of the induction system to the inlet side under deceleration. The undesirable peaks in the boost pressure that can occur when the throttle valve is quickly closed are reduced. This means the diverter valve plays an important role in terms of the engine acoustics while protecting the components of the turbocharger.

Based on the specific mention of "under deceleration", emphasis mine, I don't think the diverter valve is relevant to my scenario of zero boost pressure under constant 3,400 RPM...

Turning to the wastegate, my understanding is that it is typically controlled by the pressure on the intake side. The wastegate opens when the boost pressure exceeds spring preload. In the case of the N55, the wastegate is electronically controlled, which I am assuming means that the "spring preload" can be adjusted?

The wastegate valve is used for the purpose of limiting the boost pressure and is already known from previous BMW turbo engines. It is vacuum operated and electronically controlled through a vacuum control solenoid by the DME (ECM).

Still, even if the spring preload can be adjusted, I am having trouble imagining that it can be open both under nominal intake vacuum and under high boost.

So, back to the original question... Is it normal for an N55 to produce zero boost at high RPM when throttle is not near wide open? And, if so, how the heck is this physically accomplished?

Thank you!

[Turbod]

I have never heard of Ultra-gauge. Are you sure it is configure to look at the correct parameters? Does your car feel like it is operating normally? You should be able to build a few psi even under light throttle.

[makke]

Turbod, thank you for responding. Yes, I am quite certain that UltraGauge is looking at the correct parameter. The parameter is called "Bst PSI" -- it's in the right bottom corner of the image:

https://photos.app.goo.gl/VfQNbiWUTN32zTBG7

I have since added another parameter that measures intake pressure. The two readings correlate as I would expect. -0.6 psi boost and 13.X psi intake and, say, 7-10 psi boost and 20-23 psi intake under WOT.

Does your car feel like it is operating normally?

This is what I am struggling to answer to myself. I have only owned the car for a little over a year, coming from an E90 (2006) 325i, which I still own. The short answer is that it "feels normal" given my short experience with it, but now that I have the data from the UltraGauge, I am not quite certain that "my normal" is "actually normal" for an N55.

What do I mean by that? The naturally aspirated N52 in the 325i, with, mind you, 187K miles on it at this point (I am the original owner) feels like a turbine or a rotary. It just purrs its way from idle to red line. It is perfectly linear and repeatable. The motor loves to spin. It's not very powerful, but it is beautiful.

The N55 on my 135i is not like that and has never been. Nor did I expect it to be -- as a turbo motor it has a different character by design. Sometimes it has a little hick-up around 3K RPM. Sometimes not. It's not as willing to spin -- feels like it starts fighting you as the revs build. This is under part throttle. Under WOT, there is a definite extra shove when the turbo spools up. Under part throttle, there is not. So the N55 has never felt as good to me as the N52 does. What I am wondering now is if that hick-up and non-linearity around 3K is actually not normal and that something may have been a bit amiss for some time...? (Not sure if this is relevant, but the car had a JB4 when I bought it. I have removed it a few months after getting the car because I felt that it made the engine response feel even less linear than stock.)

You may be wondering why I am deep diving into performance parameters to begin with? The reason is a P0171 Bank 1 System Too Lean code that has popped up in the last few weeks. Since this is a very generic code that can mean anything from a vacuum leak in the intake to mass air flow to O2 sensors to fuel injection problems to ...., I wanted to get some data before taking it in to a mechanic. Hence the UltraGauge. The piece of data pertinent to the code is high Long Term Fuel Trim that you can see in the lower left of the picture. That's consistent with a lean condition, so the next step is a smoke test. However, while troubleshooting the code, I also noticed, you could say "by accident", lack of boost. This is a bit of a head scratcher for me. So, here I am...

Thank you again!

[Turbod]

Originally Posted by makke

Turbod, thank you for responding. Yes, I am quite certain that UltraGauge is looking at the correct parameter. The parameter is called "Bst PSI" -- it's in the right bottom corner of the image:

https://photos.app.goo.gl/VfQNbiWUTN32zTBG7

I have since added another parameter that measures intake pressure. The two readings correlate as I would expect. -0.6 psi boost and 13.X psi intake and, say, 7-10 psi boost and 20-23 psi intake under WOT.



This is what I am struggling to answer to myself. I have only owned the car for a little over a year, coming from an E90 (2006) 325i, which I still own. The short answer is that it "feels normal" given my short experience with it, but now that I have the data from the UltraGauge, I am not quite certain that "my normal" is "actually normal" for an N55.

What do I mean by that? The naturally aspirated N52 in the 325i, with, mind you, 187K miles on it at this point (I am the original owner) feels like a turbine or a rotary. It just purrs its way from idle to red line. It is perfectly linear and repeatable. The motor loves to spin. It's not very powerful, but it is beautiful.

The N55 on my 135i is not like that and has never been. Nor did I expect it to be -- as a turbo motor it has a different character by design. Sometimes it has a little hick-up around 3K RPM. Sometimes not. It's not as willing to spin -- feels like it starts fighting you as the revs build. This is under part throttle. Under WOT, there is a definite extra shove when the turbo spools up. Under part throttle, there is not. So the N55 has never felt as good to me as the N52 does. What I am wondering now is if that hick-up and non-linearity around 3K is actually not normal and that something may have been a bit amiss for some time...? (Not sure if this is relevant, but the car had a JB4 when I bought it. I have removed it a few months after getting the car because I felt that it made the engine response feel even less linear than stock.)

You may be wondering why I am deep diving into performance parameters to begin with? The reason is a P0171 Bank 1 System Too Lean code that has popped up in the last few weeks. Since this is a very generic code that can mean anything from a vacuum leak in the intake to mass air flow to O2 sensors to fuel injection problems to ...., I wanted to get some data before taking it in to a mechanic. Hence the UltraGauge. The piece of data pertinent to the code is high Long Term Fuel Trim that you can see in the lower left of the picture. That's consistent with a lean condition, so the next step is a smoke test. However, while troubleshooting the code, I also noticed, you could say "by accident", lack of boost. This is a bit of a head scratcher for me. So, here I am...

Thank you again!

If you were to press the throttle pedal about 30% at low RPM you should feel an initial increase in power followed but a second wave if you will of torque as the turbo builds a few psi. If you had a boost leak large enough, as your gauge is indicating, then the car would have a check engine light on. I assume your vehicle is stock? The factory chargepipe is a common failure point should you actually have a boost leak. I have performed a pressure test but never a smoke test so I don't have any advice on that front.

[anjuna]

Originally Posted by makke

Not getting much traction at 1Addicts. Thought I would try the e90 sister forums...

I have recently installed an UltraGauge (http://www.ultra-gauge.com/ultragauge/) to keep an eye on my 2012 135i with 50K miles on the clock. One thing has jumped out at me that I don't understand. I am only getting boost when at WOT or close to it. With smaller throttle inputs, I get no boost regardless of engine RPM. Here is an example:

https://photos.app.goo.gl/VfQNbiWUTN32zTBG7

This engine does not have vacuum in the intake manifold. It runs valvetronic. The intake manifold is kept at/near atmospheric. The intake valve lift is adjusted instead of a throttle body opening. HOWEVER, there is a throttle body - it is kept NEAR wide open under standard operating conditions, but is closed slightly to help control overboost and perform other interventions.

At 3,400 RPM, Boost PSI is showing -0.58ish which, I believe, is nominal vacuum in the intake. I can rev it up all the way to the 7K red-line and still have zero boost if I do it without large throttle input. The only way I can get boost (up to about 10 psi) is by stomping on the gas pedal...

Is this normal behavior? If so, how the heck is this accomplished?

Read above - in fact, at a higher RPM and lower load (as shown) you may end up with slight vacuum in the charge pipe/intake manifold.

To my understanding, there are two methods of controlling boost built into the system. Method 1 is via the wastegate valve on the exhaust side of the turbo and method 2 is via the diverter valve on the intake side. Looking at the latter first, here is BMW's description of the diverter valve in ST916:

Speaking from a pneumatic wastegate (PWG) car - In order for wastegate control to have an effect, we need to be making boost. The waste gate pilot valve (sometimes referred to as the wastegate solenoid, with the operation called WasteGate Duty Cycle [wgdc] being referred to as the amount of time the pilot valve is closed vs open) pulses to move intake manifold pressure away from the wastegate.

This means that we are constantly putting intake/chargepipe pressure on the wastegate diaphragm. The wastegate is, by design, held closed with a spring. I do not know the value on the stock N55 wastegate spring, but most are some value lower than target. Just for shits and gigs, let's say your N55 targets 9psi at WOT (forgetting the other 82347891 variables that go into the calculation for target boost) and the spring is a 5psi spring. This means that UNDER 5psi, we cannot control the wastegate and/or our impact on it's position through the WGDC (solenoid duty cycle) is VERY little. We cannot force it open - we can only try to keep it closed.

So below 5psi, you can command 100% or 0% and the wastegate position remains relatively constant.

Above 5psi (and again, these are ambiguous numbers made up), we can try to keep the wastegate position in a closed state by pulsing pressure at it (WGDC). That's why 0% means open and 100% would ideally be as closed as possible, making the most boost per turbine speed (IMPORTANT! this is why people can't make 20psi at redline on n55 - efficiency is very low at the speed of the compressor)
Based on the specific mention of "under deceleration", emphasis mine, I don't think the diverter valve is relevant to my scenario of zero boost pressure under constant 3,400 RPM...

Turning to the wastegate, my understanding is that it is typically controlled by the pressure on the intake side. The wastegate opens when the boost pressure exceeds spring preload. In the case of the N55, the wastegate is electronically controlled, which I am assuming means that the "spring preload" can be adjusted?
The spring is typically adjustable, but I am not sure exactly on the n55. This is unneccessary as the logic controller for the WGDC has an option for "additional WGDC to counteract spring" which is basically a way to command a position and counteract the spring force. Cool stuff.

You're correct about the diverter valve being unrelated to your situation. All a diverter valve does it make sure that the delta pressure between compressor stage and intake/charge pipe sides are not excessive. If we are making 10psi at 250g/s and suddenly CLOSE the intake valves (remember, this is valvetronic. you could substitute "throttle body" for more conventional thinking) we would encounter "compressor surge" because we have a fuck ton of air moving at a high pressure and suddenly the path is shut off. As such, we use a Diverter Valve to allow that mass of air back into the compressor stage inlet so it can be relieved. This is a good thing. However, if it is leaking you will show low boost compared to target boost and/or excessive WGDC. If it is malfunctioning and not working, you will hear compressor surge (think of the movie "fast and furious" and every shift in that god forsaken movie. though i still love that movie) which sounds kind of like a SHUH PSH PSH PSH psh psh (flutter) on decel.

Still, even if the spring preload can be adjusted, I am having trouble imagining that it can be open both under nominal intake vacuum and under high boost.

So, back to the original question... Is it normal for an N55 to produce zero boost at high RPM when throttle is not near wide open? And, if so, how the heck is this physically accomplished?

YES! Also, RPM does not produce more air volume passed through the engine. That's entirely related to throttle position, boost, and VE. I can make 20psi at 1500rpm. I can make 20psi at 3500rpm. I can make 14psi at 6500rpm. Those are all at WOT.

I can also make slight vacuum at all of the engine speeds listed. I just don't push on the loud pedal.

In fact, lowering airflow and raising power would be a tuner's wet dream. Imagine a world where you consumed as little air as possible and made the most power as possible. This means excellent gas mileage AND allows us to keep the compressor in the most efficient area. This is also why smaller turbos make for great driveability and poor top end power whereas larger turbos make for not-as-great driveability and greater top end power.

Thank you!

Hope that helps.

[makke]

anjuna, WOW, that was very big and very red!

You are probably saying the same thing as drwillb here:

https://www.1addicts.com/forums/show...2#post25584842

His explanation registers a bit better with my brain.

Thank you for taking the time to set me straight!

[anjuna]

Originally Posted by makke

anjuna, WOW, that was very big and very red!

You are probably saying the same thing as drwillb here:

https://www.1addicts.com/forums/show...2#post25584842

His explanation registers a bit better with my brain.

Thank you for taking the time to set me straight!

yep - we are saying something similar. there are just more words in mine.

also, didn't feel like breaking it out of quotes, so i hit "big and red"