Mark P

I've added an MBC in parallel with my N75. It's done a great job of removing overshoots/oscillations of turbo boost. [So now I have less boost than I did before adding it.] However, every so often since installing, I've gone into limp mode with a "Charge Pressure Maximum Limit Exceeded" DTC (and only that one). The moment it goes into limp mode is when I am in partial boost, never WOT.

This leads me to think that it is not only a static peak value (ie ~1.55bar) that causes this DTC (because I am no where near that), but also maximums at various loads? Maybe the MBC is causing boost to rise quicker at onset and thus is more than expected, though still only <12psi or whatever?

Does anyone know if there are other triggers to get that DTC without actually hitting some high value?

I almost wonder if the bleed hole on the MBC is causing an extra amount of lost air that the MAF had measured and thus calculates the boost higher than the MAP sensor reads??? I don't know - just trying to thing of other reasons how this could occur???

Furthermore, I have a buddy that doesn't post here. He's added K04s and put a diode across his MAP sensor to limit the boost that the MAP sees. We VAG'd and sure enough the most it ever sees is 2030 mBar. However, he's also gone into limp mode with the same DTC (and also a MAF one as I recall).


Thoughts??

VerrÜckt

I would suggest the MAP clamp for you. My first guess would be that you are building boost quicker than the ECU expects. That's something that's cheap, easy to install, and easy to remove if it doesn't work. It should also improve your timing.

MarkS4

Correct, it's in the deviation req vs. act.

daves4

That's what i think IMHO. The difference between req vs. act.

JasonS4+Festicle

probably because of a difference in "actual" vs. "requested" secondary to faster onset of boost...

I put in a TCD (the MAP clamp) and have no more problems.

Mark P

the MAP clamp will do just that, "clamp" the value once it reaches a high value. It's not going to have any effect at lower boost where I suspect my problem is occuring.

Mark P

I've seen that happen as people *replace* their N75 with an MBC and thus the difference causes throttle cut.

VerrÜckt

smoothed things out. In the higher gears, I could get high boost levels at lower throttle positions.

VerrÜckt

Me as well.

flame monkey@PEBFATS

APR S3 is too conservative for any of that, plain and simple.