Hello all.

I am the proud new owner of a 2000 audi s4 with the 345 hp MTM upgrade (and now a made from scratch c02 intercooler sprayer). Just for a little background, I've worked on cars for many years, so i tend to know my way around an engine bay....anyways....


The car is great, I really love it but i noticed something odd. After the car is warmed up, If i get on it, it would stall out, as in, around 4500 rpm loose forward momentum. If you shifted, it went away, but the car felt a little slower. So, I hooked up a boost gauge and found that at first, it is allowing the car to run to 10psi one time, which it then "cuts off" or stalls it out. After that, it rips it to 6/7psi with no problem. The car currently has a check engine light on for the passenger side cat conv below threshold, which will be replaced soon by another set of high flow cats (since it already has the MTM high flow). I was reading about the vehicles systems in the tech self study (http://homepage.mac.com/edyjun1/S4/p...ne_english.pdf) and on page 25 it says " The monotronic regulates the charge pressure for both chargers via the solenoid valve for charge pressure control G31. If a defect occurs in one of the cylinder banks, (eg melting of a cat convertor or blockage of the exhaust system) a purely mass air oriented system would still try to provide the computed air mass. This would lead to an excessivly high charge pressure".

So, here's what i'm thinking. Is the ecu "seeing" the blockage the first time, realizing it would create a potential harmfull situation, and then limiting the boost level?



Any help would be appreciated!

 

Most likely the cat, but could be the N75 or EGT sensor?

 

I would think it would throw a code for at least one of those sensors if it was...

 

Forgot bout that

Was thinking MAF too?

 

again, i'd figure with the sophistication of the electronic controls in this car, that if that were the case, it would throw a trouble code....hell, i imagine if i passed gas and it was rank enough, it would throw a diagnostic trouble code....

 

Something is puting the car in limp mode. I doubt it would be the cats causing the problem....I've had the code for both my cats and still able to have the car run normally. Maybe be the MAF as others mentioned, or maybe the N75 valve.

 

i realize the code for the cats will not cause it to go into limp mode, its merely an emissions check. but do you not think that if the ecu "saw" the excessive pressure from a blocked cat, that it would put in into limp mode? as it implies in the section i quoted previously?

 

Welcome to Audi.

You have achieved limp mode. This happens when the ECU can no longer compensate for your problem.

If you have a CEL, get it checked out, most of the time, it will tell you what the problem is, or at least what system.

It can be a simple little boost leak, dirty MAF, bad DV's,etc...

If you do have a clogged cat, you would see misfires on that side, or at least a change in boost from side to side.

Go to any local auto parts store, and have them read the codes, list them here, then we can help you, or just buy a VAG-COM and do some logs.

What's in the MTM 345hp kit?

 

the code is for the passenger side cat below threshold, last time i checked a day or so ago, i'll prob have it rescanned today....


the mtm kit incudes high flow cats (which were put on when the car was new, so its no surprise they are crapping out), downpipes, ss exhaust, chip.

 

i dont mean to sound rude in my replys, but i honestly feel that no one really read my first post, but rather skimmed.


i am planning on replacing the dv's with the tt part soon, and also, the charge hoses were replaced with the upgraded silicone hoses not too long ago.