Hyperactive PID, bad pre-control or turbo out of adjustment?

martinlink

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Hi!

Still trying to get the car dialed in. It's a BMW E46 320d 150hp, 2.0 litre common rail straight 4.

Turbo: Garrett gt1749v with Melett internals, VNT gen 1, vacuum actuated
ECU: Bosch EDC16C31
Mods: full decat (both cats emptied), EGR delete with blank on exhaust manifold, remap.


The problem:
The turbo was refurbished and the stop screw and actuator rod length were set through trial and error by me so that with the stock tune everything was great - quick spool, no over/undershoot.

After applying the tune, it started spiking very mildly, followed by a big dip in boost and IQ. N75% does not follow N75 pre-control maps (neither regular or transient) so it must be the PID taking over in closed loop mode.

I've put it down to the free flowing exhaust and increased fueling with the tune, and I think it's the PID that is a bit too spastic, reacting to the quick rise of boost by dropping N75% a bit too much.

I have tried to reduce the PID factors around the spike and this has resulted in a smoother N75% (just a little bit) in 3rd but 4th is still pretty erratic.


Here are the graphs in 3rd and 4th gear, WOT:




Green line is N75 duty factor (scale on the right side). I can also provide the .csv logs and the tuned and original files if anyone could take a look at them :)


The question:
Does this look like a too short actuator rod? Or a problem with the boost request vs actual deviating too much for too long, causing the PID controller to go ham on the pre-control maps?
Should I try lowering requested boost before 1800rpm to try and calm down the PID?


Any input is very welcome! :)
 

Enabled

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I recognize you from somewhere :)

Sorry I ran out of time and couldn't look at your file some more. But PID control is one of the most challenging things in tuning.
 

martinlink

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Haha yeah, I've done a lot since I posted there and they don't allow links from other sites so I couldn't be bothered to upload the pics again etc.

I'd be comfortable tuning and testing the PID more extensively if I actually had the map locations for the "small stuff" like borders for positive and negative deviation of boost (but I'd need Damos for that, which I can't find...)

For some reason I'm convinced I can get it better through hardware adjustment, just not perfect.
 

TDIMeister

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Hard to get a context of things of whether there is really a problem, because the in the first case actual MAP meets requested in 2 seconds starting from 1500 RPM, not a bad result in and of itself. As for boost pressure oscillations, I have seen worse results too, but if you know where to go into the mapping to alter the PID gains, reduce P just a little and increase I. No change in D (actually most turbo boost controllers are PI, not PID).

 

martinlink

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Thanks for the reply!

Spool time is pretty reasonable and I'm not too bothered about getting it any faster.
The oscillations are, however, bad enough that fuelling is reduced during the dip and this can be felt at a flat spot (moreso in 4th and 5th). That's what I'm trying to fix.

In the graphs above, I'm running a tune where all PID gains have been reduced by ~50% around the spike and dip, yet this seems to only have made the 3rd gear pull a bit smoother.

I can't help but think that the actuator might be a bit too short for this set up so the changes in N75% don't have a big enough effect on boost. Also maybe the requested boost should be reduced to reduce the deviation, ultimately giving the PID controller less reason to work. Getting the pre control maps closer to reality is also a priority, I would think.
 

Digital Corpus

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:D SOMEONE SAID PID!!! SOMEONE SAID PID!!! :D
Okay, seriously though, this is a tough cookie to crack. I'm a little busy at the moment, but I'll explain how the MSA15.5 & EDC15 ECU software sets up the PID control. I might need to go plagarize some stuff from ecuconnections.com on this topic.
 

martinlink

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Haha, seems like PID is a swear word around here :D

I ran some tests yesterday with the N75 and boost requests reduced dramatically and the result:
Underboost, but I still get the "flat spot" or dip in boost pressure, even though actual boost never comes close to requested... Makes me think there's something else the N75 or boost is reacting to, not the spike.

Edit: here it is, 3rd gear WOT


Also to note, it's completely smooth when not at WOT or from a higher RPM.
 
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KERMA

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The boost pressure governor is a by pass PI-governor, i.e. the correcting variable of the PI-governor is added to the open loop control value. A DT1-governor lies parallel to the PI-governor. Because the governor loop of the VTG turbocharger changes during operation, there is controlled adaption of the governor parameters.

The governor parameters depend on the governor deviation and the engine speed or gear. Monitoring shuts off the output from open and closed loop control at certain system errors and supplies the actuator with default values. (ie limp mode)

The boost pressure is governed to the setpoint pressure using a PIDT1-governor with parallel open loop control. Governing remains switched off for low quantities.

Governing is switched on only if the fuel quantity exceeds an engine speed-dependent threshold.

At switch-on the I-component is set to Zero. If there is a deviation at switch-on of the governor, the P-component causes a step at the output.

The D-governor is switched on in a way that its output is Zero immediately after switchon.

Governing is shut off if the fuel quantity reaches or falls below an engine speed dependent threshold. Also at shut off the on/off ratio at the output will change in a step, because the correction variable of the PIDT1-governor is not added any more. If the governor is shut off, no monitoring of the governor deviation is carried out.

Controlled adaption of the governor parameters

The boost pressure is governed by a PIDT1-governor. Here the fixed values are valid for the I- and P-parameters. For small signals inside the window the small gains are valid. For large signals with governor input values outside the window the large gains are valid.

For the DT1 element following is defined: for small signals inside the window the small gains are valid. For large signals with governor input values outside the windows the large gains are valid.

Due to the VTG-turbocharger the governor loop changes during operation, which requires controlled adaption of the governor parameters. Therefore the I-, P- and D-gain of the PIDT1-governor are multiplied each by one of three factors. The three factors are determined using curves. Input value of these curves is either the fuel consumption, the engine speed or the gear. The DAMOS-switch cowLDR_ADA selects if the factor depends on fuel consumption, engine speed or gear.

The P-gains are multiplied with a factor from the associated curve. The result is the current P-gain of the PIDT1-governor.

The I-gains are multiplied with a factor from the associated curve. The result is the current I-gain of the PIDT1-governor.

The D-gains are multiplied with a factor from the associated curve . The result is the current D-gain of the PIDT1- governor.

The memory factor is interpolated from the curve. Here again the DAMOS-switch determines if the fuel consumption, the engine speed or the gear is used as input value for the curve. Each alteration of the switch requires a new DAMOS-run necessary, because the specifications (conversion formula) change.
 

KERMA

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and to the OP, take a good look at your injection window. I think you are barking up the wrong tree with the turbo PID
 

martinlink

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Thanks for the clarification about the PID! I read up on the system from the German "Funktionsrahmen" PDF but not everything was clearly understandable thanks to my mediocre comprehension of the German language :D

Of course, making alterations to the single value variables in the PID system (namely the positive and negative deviation limits for the controller to kick in) would be easier if I actually knew where they are located in the software (I have yet to find a DAMOS for this version).


Regarding the injection, I've been logging it along with the boost graphs for quite some time now and all I've noticed is that both requested and actual IQ follow boost pressure, e.g. when there's a dip in pressure, there's also a dip in IQ. Is this indicative of something, or how should I interpret these results?

Here's a log with the IQ req and actual, in image form:



Dip at timestamp 2.6s. This is 3rd gear, 4th is way worse.
N75 drops already before that point - the root of all problems? :confused:

I can provide the .csv logs, just can't find a way to upload them here directly.
 

KERMA

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I can't make a sweeping declaration to single out something "just change that" because I don't have enough info about what SW version and car and what's been done. But this may be good example to illustrate the cascade effect of interdependencies between the different control areas, that you may not think are linked - but they are. Start changing one thing and there is a cascade effect that gets more complicated the farther you get from stock.

But generally speaking if the power is fluctuating with boost irregularities, then take a look at your smoke map(s). The smoke map should NEVER be the limiting factor in the meat of the power band. Only at low rpm below ~2000 and high rpm *perhaps*. Those 2 things (boost/smokemap) kind of feed on each other when there are problems making everything worse. So First when it's a new/unknown car, find which smoke map(s) are active and eliminate it from the picture for development purposes. It can be fine tuned AFTER the fueling, Patm torque limiters, etc are settled upon. the There are too many tunes out there (even "pro" ones) that rest on the smoke map after raising the Patm torque limiter to the sky (which eliminates its influence). It's easy to get good "numbers" this way but driveability can suffer and it is crude. You need the WOT limit to be stable above all else or you can't adjust anything else reliably. for instance sometimes the boost governing parameters is based on the limited/filtered IQ values, while the ""desired" boost is based on raw throttle. So if you have an unstable base for the control values it will never be a stable tune. You will get that "perfect log" one tiime then the next time it will be wrong (but guess which one gets posted on the forums) . The 2d torque limiter is much more stable and gives a much better refinement and smoothness at WOT than simply resting on the smoke limiter or even worse, at the outer boundary of a fuel map. That is amateur stuff but sadly it is also the proponderance of what you will find in the industry, even among the "most respected" tuners (especially on these forums). You need to calculate WOT and set the 2d torque limiter FIRST, to get the correct start/end of injection.... then EVERYTHING follows that. none of this "here is the address for that map and this map and they should be adjusted." Get the basics down first then build out the tune from that. And by the basics I mean study the stock file to see what the factory did FIRST! Thendo the math to decide what you want to see for injection window and make that happen, then tweak the turbo to act right, then tweak the smoke map. Of course this is an oversimplification (like everything on the forums) and I'm sure there will be someone to say but but you are wrong on this or that nitpick thing. But this is what you do if you want a good tune.
 

KERMA

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What I'm trying to say here is, stop looking at the PID until you get the basics right, first. That's NOT the first place to look "just becuase you can" (a common trap for noobs- oooh look shiny new map to change lets change it so we can say we did)

If you get the timing/duration correct then everything else comes a lot easier, trust me on this one. But it's a grind and work and not necessarily as easy as adding or subtracting a few percent from "the right map at this address". Everyone wants easy and someone to save them from doing the tedious/ginding work but that's what you are signing up for if you want to DIY.
 

martinlink

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Now THAT'S what I call an explanation! :)

Thing is, the PID modification was suggested to me by a few experienced tuners as just a "test". I tried it, got some mixed results and now I'm trying to do it the correct way, slowly but surely.

As I'm just at the start of the tuning journey, I'm not yet comfortable at finding (and changing) maps I'm not too sure about, especially working with publicly available "map packs" and other forum users' posts...

What I've found until now is that the BMW EDC16C31 does not have a "classic" smoke map (as in RPM vs MAF/MAP), but rather uses the lambda maps - it has been noted that these are lenient enough that they should not be touched in everyday tuning. Not too much other info on it so I'm afraid to touch it in case I mess something up :(


I'm working with a tried and tested tune for an identical car as my "base", which has proved smooth and stable when used on a car with stock hardware. My issues are most probably caused by the decat (only muffler on the end of the exhaust pipe, nothing else restricting flow) and the refurbished turbo which came mis-adjusted so I had to adjust both the stop screw and actuator based on logs and the 1400rpm test, N75% altering between 0 and 100%. This set of modifications is why I can't use the tune as-is and have to make adjustments to suit these modifications.

I've just made another version with the boost request lowered between 1250 and 1750rpm to decrease the deviation; and increased after that until 2250rpm to give the actual boost some space. I've also reduced the transient N75% between 1750 and 2000rpm to match the logged values. The only thing stopping me from going out and testing this version is the fact that it just started snowing :confused: in late April???



By the way, if you'd be willing to check the file(s) out, the software number is 361858, available pretty much anywhere. I can also provide the modified file in case you have time to spare - in this case, name the preferred upload location and I'll throw it up ASAP.

EDIT: I uploaded the base file + log as well as the new (v6) adjusted file on google drive:
https://drive.google.com/open?id=0B7maSoz2vMw2bmc1RWxxWm9ic0k
And here's the stock file:
https://drive.google.com/open?id=0B7maSoz2vMw2SF9pVDVjUWIwOVU


 
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martinlink

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I finally had the chance to test out the v6 file in the last post where transient N75% is lowered a little and boost request is closer to the actual output of the turbo.

It is miles better than before and IQ does not drop despite the remaining small dips in boost. There's a point where IQ stays at the same level for quarter of a second but nothing too bad, at least not enough to be felt. In 4th, starting from a higher RPM gives even smoother boost curves and not so much dipping - maybe this is a clue? :p

I tried changing N75 both ways from this point and nothing seemed to affect the performance (at least not positively). Yet it's still far from perfect :(
Any ideas what to try? Or am I at the point where more advanced modifications are necessary to get it as smooth as a stock car?

3rd:


4th:


4th from 1600rpm:



Here are the logs along with the tuned file:
https://drive.google.com/open?id=0B7maSoz2vMw2SDJpNGh4VW1tNnc

As always, any input is appreciated :)
 
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Digital Corpus

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So Kerma provided a more detail explanation than what I was about to. Thank you for your input for being so detailed. This and the fact that I'd be referencing older software than what you have so there would have to be some discrepancies.

To re-touch on some of the fundamentals though that he mentioned
  • Don't touch the individual P, I, D, or Dt settings unless you absolutely have to as they are last resort.
  • When the ECU decides to engage PID control, something is a wee bit off with your control map.
  • When PID control is on, it is determined by fuel consumption in l/hr.
  • Make sure you've covered your basics first

There are several components responsible for controlling the vanes of the turbos. If you have a vacuum based system, the simplified list is the PID & Dt values, the control map, the conductance of vacuum & atmospheric pressure lines to the solenoid, and the setup of the vacuum actuator.

Even on the fancy vacuum actuators, if the conductance of the vacuum line creates a slow response time of evacing the atmospheric pressure, the rest of the pieces of the puzzle cannot work properly. You mentioned that you kinda eyeballed the setup of the actuator so if you don't have it setup to where you're operating in the suggested 3-5 mmHg to 17-20 mmHg range, then you can get erratic behavior.

In the early ECU software versions there are 3 types of maps that control the vanes and you've already acknowledged their existence: control map, min & max duty cycle maps, and the P, I, D, and Dt maps.

Since the PID control is often engaged even in a stock car, the simplest method for setting up a new turbo for the turners is to modify the min and max duty cycle maps. It works, but it's really not the best way to do things because the duty-cycle-to-MAP (in the control map) values in the control map are so far off you can spike pressures and have then dip way below with the right conditions due to transient response.

The "proper" and very very time consuming method is to tune the control map. If everything then matches with the driving range then you're good. The min/max maps control whether or not you accidentally slam your vanes shut and spike your EMPs or open your vanes too much and loose exhaust energy; in essence they are software safeties in even you have malfunctioning hardware. The there are the one dimension P, I, D, and Dt maps.

PID tuning is really hard when you don't have controlled conditions, i.e. your engine and turbo in a lab on a dyno without a chassis. Essentially these are to allow transient response to happen properly with appropriate amounts of undershoot and overshoot. They can be tuned to be mild, moderate, or very aggressive in change in duty cycle which puts stress on the physical hardware (turbo). Only after you have corrected everything else should you touch them.


Go back and make sure your actuator is setup appropriately. If you can run a shorter line to the actuator, then do so. If you can make that line have a larger ID, that is even better. If you are able to borrow the N75 map from an ALH ECU but increase the duty cycle by 5%, as in 45% to 47.25% not 45% to 50%, and use that as a springboard, then do so.
 

KERMA

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[*]When the ECU decides to engage PID control, something is a wee bit off with your control map.
no.

PID is ALWAYS engaged as "the other part" of the governing process.

Let's say that the "N75 map" is half of it and the PID is the other half. Manner of speaking.

N75 basis map (aka "the N75 map") is always active. At certain conditions (low load or idle for example, aka open loop, aka precontrol only) it is the sole factor determining your N75 duty cycle at any given moment. But when the governor is actively regulating boost (most of the time) there are 2 components to what makes up the N75 duty cycle at any given moment: the N75 "basis" map *AND* the governor gain. The Gain is dynamically calculated on the fly according to PID... and added (+ or -) to the "basis map" to arrive at some duty cycle.

In other words "the N75 map" is just a starting point.

You can affect how the boost behaves by adjusting that "starting point" up or down. This map is experimentally derived on the dyno, and is designed to minimize the magnitude of the correction "gain" in the PID amplifier so to speak. But make no mistake... the active regulation/governing is almost always "on" and therefore it IS using "PID" almost always- even if a small amount.

the active governing is necessary becuase the operating conditions that determine boost are never the same. rate of throttle request, starting speed end speed, start throttle position, end throttle position, micro fluctuations in throttle position, slope of the road, coolant temperature, altitude, could all be different every time you depress that throttle or change throttle position so no 2 transients are ever exactly the same. So really there's only so much you can do with one map or the other, it all has to be considered as a whole and part of an integrated system.
 

Digital Corpus

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Fair enough. Though it may not be apparent that PID is active when in a steadystate mode ornate driving, it is active. I'm used to thinking of having the precise duty cycle from the map benign what is used as PID being deactivated, but yeah, it's never really off.
 

KERMA

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I dunno maybe a better way to say it is:

the "N75 map" is for a "static" condition
the PID gain is to adapt that "static" value to compensate for transients and recover afterwards

Think of how the N75 map is made. Engine on the dyno, in production hardware form. Ok run the engine at 15 mg/r, 1500 rpm, and adjust the duty cycle manually until the specified boost for 15mg/r is spot on. Now repeat for 20 mg/r. then 25 mg/r, then 1700 rpm, and so forth. This is an artificial set of conditions that will never be seen when the engine is in a car on the road. Real life will be dynamic and ever-changing. You can't ever get the same exact conditions or a stable condition for very long. That's why you need a way to dynamically adapt on the fly. The governor is what adjusts things on the fly and it uses PID components to try and figure out what adjustment is needed at any given moment.

When you change the operating parameters, by adding injectors, tuning, timing, duration, changing the turbo, camshaft, etc, you are changing the pressure and flow and temperature conditions in the exhaust manifold from what existed during the engine dyno sessions when the N75 and governor parameters were determined. SO these turbo control things must be adjusted if you want the engine to respond in the same way. (or change it till you get the response that you want).

In order to get 100% perfect you can't just do one or the other.

And you also have to look at the primary reason that the turbo stuff is out of adjustment in the first place- what is changing the conditions in the exhaust manifold from stock? And what has to be done (or can be done) to influence the turbo in a favorable way?

Is it a turbo control system causing the problem or is that just a symptom? What I see in the OP situation is a turbine drive problem caused (or exacerbated) by whatever is changed in the fueling parameters. THAT is what I mean by "the basics". Of course this is a lot of assumptions based in incomplete info so just take it FWIW. But hopefully I added something useful to the collective knowledge base even if it is not everything

Too often I see the dog chasing his tail about the turbo control logging and retuning and relogging and frustration when the right question isn't being asked in the first place.
 

martinlink

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I'll note down some observations I've made over the months I've been dealing with the issue.

1) PID control is set to turn on above ~20mg IQ depending on the RPM, this means that during very smooth and controlled accelerations it does not stay active. During any sort of acceleration, it is designed to turn on almost immediately.

2) I've logged a fair few identical engined cars, both manual and auto, and even with the stock software, the requested boost stays way above what the turbo is actually capable of below 2000rpm -> PID is active on them as well. The N75 duty cycle makes a similar downward spike on those, yet the boost response is less violent (rather smooth and round) so the pressure never dips below desired. I'm lead to think that the free flowing exhaust and perhaps out-of-adjustment turbo make my boost respond to changes in N75 faster and with more amplitude, hence the dips. This was the theory behind the need to reduce the PID gains, since less input is required for the same amount of change.

3) I've had a chance to look at some stock turbos for these cars. The stop screw has always been set just a little bit longer than mine is at the moment and they tend to hit full requested boost at ~2100rpm so a little later than mine.

The actuator rods vary from 8 to 9 turns visible. Mine was originally at 8 turns and used to spike ~150mbar above req even with the stock tune. This was exacerbated by the tune, which made it spike ~250mbar above req, dip a little under req, and then hold a steady pressure ~100mbar above req until redline. As it was bad in 3rd and 4th was even worse, I decided to lengthen the actuator to 9.5 turns visible where it's at now - this reduced the spike to an acceptable level but made the dip bigger!
So maybe the actuator should be set to the original setting where the pressure almost never fell under req, and then the N75 should be reduced until the initial spike and sustained pressure come down to requested levels. I have a suspicion, though, that this will cause the dip to become bigger as well.

4) During my testing, the effect of modifying the base N75 values has been negligible in the range where PID is the most active (that is, between 1500 and 2250rpm) - to see any effect I have to make changes way above 10%. After 2250rpm I am able to affect the sustained pressure through 1% changes. This shows the power of the PID governor, which is perhaps another reason why people tend to lean towards modifying it, sometimes without even trying to get the N75 base map right. Yet I believe that in some cases, it is impossible to make things ideal through the base map values and inevitably PID will have to come into play.
 

martinlink

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I am finally done with university (so now it's an MD trying to fix the car!) and have enough time to run further tests etc.

At the end of the previous page there was a suggestion about the vacuum tubing - the shorter and larger ID, the better... It seems this would be counter-productive as a shorter and smaller ID tube would hold less air that needs to be moved. But the point about the tubing being a factor is a valid one.

I am currently running a fairly short 2.4mm ID (OEM) tube from the N75 solenoid to the turbo actuator. Maybe this is what is causing the boost to be so "snappy" and over-reactive to the changes in N75 duty factor? As a proof of concept, I should try one that is way longer and see if it has any effect.
 

martinlink

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Hopefully, though the placement results aren't out yet. Depending on that I have either 2 months or a whole year to fix it :p
 

Digital Corpus

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the stock PID control creates an intensional spike. This is not caused by sluggish evac-ing of the control line. If you'd like some links regarding vacuum systems, I can provide.

In pressurized systems the concept of flow is referred to as restriction. In vacuum systems the concept of flow is referred to as conductance.

A shorter, fatter tube would facilitate the solenoid's command for the appropriate level of vacuum for the vane position to affect the physical system is a closer-to-real-time manner. A longer narrower tube would do the exact opposite.
 

martinlink

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So if I wanted to calm down the currently over-reactive actuator, I should get away with a longer vac pipe between the solenoid and actuator - in theory, this would make the actuator move less for the same amount of change in N75 duty %?
 

Digital Corpus

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The simplistic view would say yes, but if you slow it down that much, expect boost codes, constant underboost driving, and more importantly overboost driving, and limp mode, I'd wager.
 

martinlink

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It has been ages now but today I finally managed to fix the issue.

First off, the vacuum line length did nothing to alleviate the twitchy N75 duty %.

What finally helped was lots and lots of logging to recreate the N75 transient maps from scratch, along with toning down the effect of the PID controller. I turned down all three factors by over 50% and adjusted the N75 values to more closely follow the real-world requirements - the result is a perfectly smooth boost curve, the way it's meant to be :)

2600mbar at 2100rpm in 3rd and 1800rpm in 4th, holding rock solid until 4200rpm. Could probably do more but it's scary fast as it is :p
 

martinlink

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Heh, that's a good way to put it :p

Now, in hindsight, I'm sad to have let the patient suffer so long... Guess that's what you get for trying to save the world on all fronts - sacrifices had to be made.

I'll keep messing with the tune to try and make it a bit more economical now. I'll start by opening the vanes by 5% at cruising rpm/IQ and also where the EGR used to be active. Theoretically should make the engine breathe more easily and reduce consumption without affecting spool. If anyone has any tips or ideas on this, I'd be happy to hear them - until now this car has been milked for max power but why not have the best of both worlds? :)
 
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