that is a completely different car. i dont know what year the OP's vehicle is, but newer Audis like yours, and even the 99.5+ and especially 2001 B5's have more (accurate) sensors.

my 98 with a stock narrow-band O2 and no MAP sensor wont handle more then a few extra PSI over stock boost levels on the stock program before i see some significant timing pull happening. stock is 8psi, it may handle 10 or 11, but if you slap on a 15psi MBC on the stock software its going to lean out and knock like crazy.

he is also forgetting that when you put a ball and spring type MBC like the turbosmart on an already boost spike-y turbo like the turd of a k03, you will get some very harsh surging. that spiking can cause most of the original problems he was complaining about.

MBC suddenly sees the required pressure and opens all of a sudden, instantly killing the turbo, boost pressure falls rapidly and the MBC closes again and boost pressure surges back up causing the MBC to pop open again and repeat the process.

 

yea, but i think i had surging when i ran my TurboXS bleed type MBC. but i was pushing 22-25 psi with a tune tho.

it sounds to me like the boost is spiking the computer is noticing a sudden increase and cutting the fuel.

is the car bucking when you experience this?

 

that sounds right, becasue if i am too quick with the gas pedal, it will misfire at 10psi, but if im gradual it will run finr at 10psi all the way to redline. it dosent "buck" but it would sometimes feel like i ran over something big .. scares the **** out of me.. i did take off the MBC, but it still misfires if im too quick with the throttle, but in 4th or 5th if i get on it and the boost is slow, it will run fine. Do you think maybe i could have gotten a defective MBC? my boost gauge was all over the place with this thing.

 

That timing pull happens because the IAT's are going up. The wide band 02 was not used till 01 and the map sensors are just a safety sesnor, it has nothing to do with actual tuning. Timing pull does not mean the car is running lean since they are 2 completey different things. The MAF is used to let the ECU know how much it needs to adjust the fueling vs the fuel map it is running off of.

If the IAT's are kept in check then the timing pull will still be in spec and there will be plenty of fuel because of the MAF.

Actually its easier to turn the boost up on a ndbw car because there is nothing there to tell the ecu that the boost is in fact being turned up. This is an issue on the dbw cars because of the MAP sensor tells the ecu that the boost is out of spec and the ecu closes the throttle to reduce the power. This is why some dbw owners do the diode mod to trick the ecu into thinking the boost is still where it should be even though they might be running 26psi on a 15psi chip. I have seen plenty people do this on a 2000 without any problem and that car has a narrow band that is not being used at WOT just like the ndbw cars. The only difference is that the 2000 MAF has a 215 g/s max reading while the ndbw has a maf that will only read up to 186 g/s and after that point the ndbw ecu just starts increasing the fuel anyway. But not like a standard K03 is going to reach 186 g/s.