I've been trying to diagnose poor performance on my W212 E400 M276 TT and figured I'd get more responses here than the W212 forum. I recently got a Dragy to measure 0-60 with a Eurocharged tune and was surprised to be getting low 5s 0-60, which is basically what I should be doing stock. The tune is supposedly 480HP (which is probably a bit optimistic). I flashed the ECU back to stock and my 0-60 went to low 6s, definitely much slower than it should be stock.

Lots of research pointed towards a known failure point, the rubber membrane on the vacuum pump check valve. I pulled the hose today fully expecting to find it spitting oil and smoke, but it was clicking as it should, nothing appeared to be spitting out and the rubber hose was clean. I'm still going to replace the check valve just to be sure, but now I'm wondering what else could contribute to this condition? The car is over 11 years old and has 65K, has the original vacuum pump and I just assumed it would be the valve, but now I'm not so sure. I'm also not getting any sort of codes.

If it matters, I've been running a JB4 for 6+ years, but it has been set to Map 0 (no modifications) and I've just been using it for logging purposes since getting the Eurocharged tune 6 months ago.

I would log a pull and see if you are hitting target boost. Could be several other things causing slower 60mph times, how are the tires, trans been serviced? Any vac leak at the pcv system or oil in the wastegate actuators or failing/dirty map sensors. spark plugs have less than 10k on them? how about the coils. running 93 fuel?

Some things to think about

1. MAP SENSOR the one after the throttle plate. Mine went bad on M276TT and it had no check engine light. Using a diagnostic tool you can check the change in pressure when you blip the throttle (mine didn’t move)

2. A cracked vacuum line can cause a loss of boost (not only do you need to make the vacuum it also needs to get to the turbo)

3. Intake air temperature sensor on the intercooler. Use your diagnostic tool to make sure that it gives a reasonable temperature. I replaced mine because I was trying to remove the original one to clean it and I broke it

4. The TURBO diverter valve is a soft rubber membrane and it can rip and that will cause boost problems

5. A clogged catalytic converter will limit power. Hopefully your issue is something else.

6. Boost leak- check your pipes

good luck

Paul

Thank you for the suggestions Paul. I ordered a new check valve just in case, waiting for it to arrive in a couple of weeks. If they doesn't help, I'll start going down the list.

I created a thread on the CABRIOLET forum to share what I did for my M276TT

I’ve been replacing the check valve on the vacuum pump regularly but it is not working consistently. Sometimes the throttle response is awesome and sometimes it is terrible.

Because my M276TT is tuned to the stock map it limits the Torque and Horsepower. Because of this I don’t actually lose horsepower when the check valve is unreliable. Instead I lose throttle response and smoothness.

I had an Audi 2.0T Cabriolet and I tuned that engine because it was underpowered in the stock form. If you look at the dyno you will see that the stock tune has a strict torque limit and an aftermarket tune allows the torque to go up and is limited by the TURBO.

Because of this I will notice a vacuum problem as a Throttle response issue and you will see it as a peak power loss.

Hopefully this makes sense

I installed a second in line check valve to keep the vacuum level constant

Secondary check valve

Let us know what you find out

Good luck

Paul

This is great , thank you. I'm interested to see if a new check valve makes any difference even though the old one appeared ok. The existing one is now almost 12 years old, but I do only have 65K miles. Oddly enough, after removing the line to to check it and then reinstalling, performance appeared closer to what I would expect stock. I didn't do a bunch of runs and basically parked it in favor of another car for now until I get the replacement valve.

@DubVBenz

I know that you following the other thread but I am curious if you were able to improve your M276TT

Take care

Paul