DTC 17965 Charge Pressure Contr. Positive Deviation

[dodgydave]

Hi guys,

I have no air leaks and the N75 is fine.

The funny bit is the error only happens when I'm cruising not under full throttle. I've pinpointed the error in a graph (attached spread sheet). You can also see all the other values and graphs.

Please let me know if you can spot anything unusual.

My guess is that the MAP sensor doesn't meassure properly at low boost values.

Let me know what you think. THANKS !!!

Car mods are:
Large motorsport hybrid Turbos
100 CPI Cats and entire sport exhaust
SKN Chip with integrated digital varyboost. Boost up to 1.85 Bar absolute!
At 1.65Bar the car has about 510bhp

Cheers,
Dave

[Turbo Joe]

So what is the cure for this because I have got the same fault come up on my car?

[Mik]

Something to do with the fact that you are both running SKN maps? (only joking)

[S2tuner]

Hmmmm, Mik might be right here to be honest... I don't know how SKN do their maps, but I know what causes that fault code to be triggered in the ECU and I know how to get rid of it as well.... The MAP sensor does usually read accurately, unless you are getting an "implausible signal" fault code that points to the MAP sensor being faulty. If not, it is a programming error.

@dodgydave: I see you are "measuring" torque and HP in block 120 with VAG-Com, sorry to say this but it's not right and you won't have a decent idea of the power your engine is pushing.... Block 120 only gives a calculated torque value that the ECU thinks the driver wants to have from the engine, it is not calculated by any means and I don't think it is accurate. If you want to know the torque your engine produces, put the car on an accurate rolling road and then you'll know....
1.85 Bar boost will never produce 500 HP in an RS4 engine by the way, unless you have some really special turbos, which SKN don't supply....

HTH,

Mihnea

[flashyg]

how do you know the n75 is perfect?

[Turbo Joe]

Following that question, what is the N75?

[tartan_rob]

N75 controls how the pressure feed to your wastegate's therefore controlling boost levels.

[zorroRs4]

Mihnea

[dodgydave]

Hmmmm, Mik might be right here to be honest... I don't know how SKN do their maps, but I know what causes that fault code to be triggered in the ECU and I know how to get rid of it as well.... The MAP sensor does usually read accurately, unless you are getting an "implausible signal" fault code that points to the MAP sensor being faulty. If not, it is a programming error.

@dodgydave: I see you are "measuring" torque and HP in block 120 with VAG-Com, sorry to say this but it's not right and you won't have a decent idea of the power your engine is pushing.... Block 120 only gives a calculated torque value that the ECU thinks the driver wants to have from the engine, it is not calculated by any means and I don't think it is accurate. If you want to know the torque your engine produces, put the car on an accurate rolling road and then you'll know....
1.85 Bar boost will never produce 500 HP in an RS4 engine by the way, unless you have some really special turbos, which SKN don't supply....

HTH,

Mihnea

Okay Guys,

To clarify: I know that the hp calculation is rubbish!!!!!! 650+ hp In my and EVERYBODIES DREAMS! !!! Wink
1.85 Bar is the maximum pressure I can archive, which doesn't mean it's any good!! The best power is when the boost peaks at 1.65 MAX - anything more you can actually see the ignition retarding too much to counteract the knocking. The car apparently did 510 Bhp on the dyno where I'm not sure what the boost was. The guy I bought the car of said 1.65 Bar but I think it was less more likely 1.45 Bar. I testdrove Kim Collins 518Bhp and he drove mine and we couldn't feel any difference between those two. And that was when I was driving at 1.45 Bar. So, which means I must achieve more power at 1.65 as you can feel a significant difference in torque between 1.45 and 1.65.
Anyway, I will do another dyno run once I've fixed my problem as Kim and myself are keen to know the real power. Anyone who begs to differ is free to take a spin and let me know what they think. Wink

Now what I found out about the problem. First, SKN did heavily modify the electronics to allow the varyboost to work. As the standard MAP only does 1.5 Bar absolute they modifiert it. Unfotunately ist all glued together but I can spot a few resitors and an adjustable pot on top. They also modified the N75 and drilled the bottom hole bigger. That's why when I swap either the MAP or the N75 for the original parts I can't get passt 1.5 Bar even on Full vary boost. As soon as I put the modified parts back in I reach around 1.8 Bar on full varyboost.

Now, I norrowed down the problem and it is definitely NOT the MAF or the N75 as I renewed them. Also the error only seems to show up at certain outside temperatures, which leads me to believe it is maybe a problem with intake temp sensor. As far as I know the MAP does both pressure and temp. And as soon as I swap the MAP Sensor the problem seems to be gone (<-further testing needed). But as I mentioned I only get 1.45 Bar then.

I talked to SKN and they can provide me with a new sensor when I send in the old one. But before I do that I would like to get behind their mods and understand how their mod works in detail.
Anyone any ideas ?

Where can I get details for that MAP .... If I had the details I can mod my own sensor and I could reverse engineer their Varyboost. Anyone has any details ? Also, does anyone know where I can get thicker head gaskets for my RS4 ?? Except MTM ?


Cheers Guys,
Dave

[S2tuner]

Dave, there is no need to run varyboost so the turbos make more than 1.55bar. The ECU doesn't only measure/control boost but lots of other things (intentional auto-censoring myself because I can't reveal all that I know on the forum), and it can control boost so it runs above 1.55 Bar. Peter Link from MTM knows how to do this without varyboost and so do I.... Drilling N75s and so on are just bandaids IMHO....

Regarding the head gaskets, send me a PN, I can sort you out.

Mihnea

[smurfbus]

I guess that skn uses some sort of resistor+zener map clamp witch you can adjust with a pot? google for 'map clamp'

[dodgydave]

Guys,

I worked out how it works!!!

Yesterday I took all the bits apart and it's very simple.

- The resitors on the MAP sensor change the voltage signal to fool the ECO there is 0.4 - 0.8 Bar less pressure depending on the pot setting. Unfortunately, this removes the ability of the Sensor to pick up any change in pressure below +0.4 - +0.8 Bar hence the DTC, I guess because the ECU is stuggeling to meet the right pressure.
- The N75 has been drilled open to allow the varyboost to achieve higher boots pressure. (This is common practice with electronic varyboost controllers. They're always sold with a different N75)
- The Program does 1.50 Bar max with original unmodded MAP, N75 and NO varyboost

As soon as I use the modded MAP i NEED the varyboost to reduce the pressure. Otherwise, the ECU tries to reach 1.5 but to do so it needs a real pressure off 1.9 Bar ( 1.5 + 0.4 <-foolfactor), which can't be achived. That's why I can 'drive' 1.85 Bar, which is were the turbos end !!! The max the std engine can handle is around 1.65.

So, IMO this is rubbish !!! Don't get me wrong the SKN Software is great but why didn't they get a real 3KPA MAP and extended the map upwards ?? Too expensive ? Or maybe they didn't know better at the time (over 3 years ago ) ???

Anyway, my plan is now to get a 3KPA and a program that is properly mapped up to 1.75 Bar and then use the varyboost to reduce boost and NOT RAISE !! This way the engine always runs with the proper maps even when I use the varyboost because the MAP will give it the REAL pressure not something fake. Hmmm, guess I'd still have problems with DTCs then ???

Or even better, NO varyboost at all and 2 programs. One street and one race. I installed the same on my RS2 and it works great. I can switch during driving. Whilst switching the engine shakes for a sec and that's it! That way I could drive one map for 98 octane and the race map for 102 octane.

What do you guys think ? Anyone knows somebody who does switchboards for the ME7.1 ?

Cheers,
Dave

[S2tuner]

Dave, 2 programs can be done for the RS4... the switching is a little more complicated than on an RS2 but it does work.

As for the varyboost, ditch it IMHO, the ECu can be programmed so it gets the turbos to run 1.75 bar if you want 1.75, without the need for a varyboost or anything similar...

HTH,

Mihnea