Hi guys,

even though I have an S63 Coupe, I prefer to post it here mainly because there is a lack of feedback in the S63 section. Anyways, I have the same engine as W212 E63S, 585 BHP version of 5.5 BiTurbo M157. I have modified it with a Renntech Stage 2 ECU Upgrade (my thread here: https://mbworld.org/forums/s63-amg-4...de-my-s63.html ) and it all worked quite well until I replaced my stock exhaust system with full exhaust with sport cats - which should have added around 15 more horsepower, mainly because after the cats it is a straight pipe - there is no way performance can be worse after this.

After the exhaust installation the performance rapidly decreased - at first I thought it was some kind of problem with my Renntech tune, but today I have tested the performance Renntech vs stock and basically with Renntech the performance is comparable to a stock car, without tune it is very bad (60-130 MPH in 13 seconds).

We have tried to see if diagnostic tool would show anything - it showed fuel pump + engine control unit, we have removed these faults and they never reappeared, but the performance is still very poor. We have tested the exhaust if there is any leak and there is no leak. We have tested if there is any leak of pressure behind turbo and nothing is there.

At this point it seems to me that ECU is limiting the power in some way for some reason. Did anyone experience similair issues? If yes, how did you solve it?
I am absolutely running out of ideas.

Any kind of feedback will be highly appreciated!

Thx!

Seems my earlier reply does not exist! So here we go:

Just a guess, but you have changed your equipment post tune. I don't have or know how Renntech's tune works, but I would call them first and tell them what has happened. You may need to do some data logging to see exactly what the engine is doing under full throttle. The removal of the cats may have reduced engine back pressure, which can lead to a loss of boost = lost horsepower. Again, I don't know how your tune is setup to read that change and its impacts throughout the tune. So start with Renntech.

Hey bud, I would get in touch with Renntech. There is definitely a difference that needs to be accounted for when it comes to Stage 2 with stock exhaust and catted downpipes. Your stock ECU is definitely not well equipped for it. Your software probably needs to be updated for race cats.

Maybe O2 sensor? Is the fuel economy jacked implying the ECM is dumping fuel, pulling timing etc. to protect the engine?

For the record, I have no prior experience with this, just guessing.

Did you disconnect the battery recently?

Something is off, obviously. You said was running well til exhaust modification. Did you 60-130 before the exhaust mod?

After a whole day of discussing this with various experts we are now pretty sure that it is due to the replacement of original exhaust valves with different ones. It shows a couple of fault codes on the Engine Control Unit and we believe the ECU restricts boost/power, because it thinks that valves are not functioning properly. We tried installing back actuators (motors without valves) but it didn’t help.

Is there any way to make the car think that valves are there? Or switch them off entirely, or use some kind of valve simulator?

A couple of guys above me said this too, but you need to talk to Renntech DE and adjust your tune. It's your o2 values the ecu is seeing causing it to pull timing resulting in your power loss. It's not enough to throw a constant fault and put the car into complete limp mode, but it is enough that the ecu can adjust itself for what it thinks is a slight adverse, yet not catastrophic condition that you will see a stored random fault as the ecu tries to figure out what's going on. It won't necessarily be an o2 fault either. The high flow cats are the cause. Once they adjust the o2 values in the tune, you'll be back on track.

Update:
Exhaust Flappers are causing faulty codes (as attached) and this causes ECM to limit the power & torque. This is really a major issue and everyone who is after an aftermarket exhaust should note, that removal of original flappers will cause these issues. The solution is complicated - we will reconnect original flappers and "hide" them somewhere inside the trunk, so the car "thinks" that they are still there. We have tried doing this just with the actuator mechanisms without flappers/valves, but it is not enough and ECM still shows this code. So now, we have to reassemble the whole thing, so it thinks it's there.

This should solve this issue. I will keep you posted.

Not true.
I have the same car you do and installed the bypasses for the exhaust flaps and have zero issues. I also have aftermarket exhaust. Have put almost 20,000 miles on my car this way. AWE sells them for cheap.

Also that appears to be a Matco brand scanner pulling those codes. Those scanners are notorious for giving incorrect codes on Mercedes. Take it to a shop with proper MB diagnostic equipment

I didn’t have the bypasses, that’s why I got the codes. I tried searching for them, but found none. Would you mind posting a link here? I would definitely like to try them out. Is a retrofit easy?

UPDATE:
Okay guys, so flappers issue was solved and my car became a bit faster. We have cleaned all the codes using diagnostic tool and it shows none anymore. I still need to pay a visit to MB to use a proper Xentry diagnostic to see if there are any "hidden" codes. I have measured my acceleration times on Dragy and I am still running slow. I've measured it on the exact same location with the exact same weight. As you can see, 1/4, 100-200, 0-200 times are still at least 1 second off. As a matter of fact every measured value is worse than before. It doesn't make sense since sport cats + straight pipe should have made the car faster (by a bit). While 1 second might not seem much, it is great difference in terms how you feel the acceleration and how fast it goes. 12sec car is a lot slower than 11sec car.

I've visited my local Renntech dealer, consulted this with them and even tried reinstalling Renntech ECU Tune a couple of times, but it doesn't help. When I install my stock ECU tune, the car is also 1 second slower than a stock car should be.

So, since flappers issue is solved and Renntech tune is probably not the cause for this - does anyone have any idea? This stuff is becoming very weird here and I am runining out of ideas. There are no leaks around turbos, exhaust or anything else. Mechanically, car is perfectly fine.

How it was before:


How it is now:

What are the new trap speeds on dragy?

What's the weather like before vs. now where you are?

You need proper diagnostics performed by a Mercedes professional. Also stock vs tuned dyno would be extremely helpful to see the delta in power and determine if it is a tune related issue or if the engine is down on power on stock tune also

Flap simulators. Takes 5 minutes to install on a lift

Same weather, temperature and location.
Trap speeds are about 5-10% slower, I have just checked it.
1/4 mile was 204KM/H now 194KM/H, 1/8 mile was 159KM/H now is 152KM/H, everyhing is slower...

We just did full diagnostics (Xentry) today, no issues, no codes, no nothing. Car is perfectly fine.

are you still on the modified exhaust or back to stock?

I am still on the modified exhaust with sport cats (200 cel). OEM flappers/valves are connected to the car and stored in the trunk - they function as they should (probably) as no codes are shown on Xentry. I am going to order AWE Valve Simulators, but before they arrive this was the only solution to get rid of faulty codes and soft limp mode. Even though this is solved, the car is still not runing its full pontential. Obviously, the modified exhaust has its own valves and they function by remote control.

Best of luck with your troubleshooting. However, the culprit may be your modified exhaust. I suggest re-installing the factory exhaust and see if the car runs like it should or not. I've learned the hard way on other platforms that "modified" doesn't always increase performance, especially if you have not re-tuned for that modification.

Seems to be your culprit here, ditch that exhaust

Just a couple of photos to share with you. I would like to think that the modified exhaust job was very satisfactory. As for my 200 cel race cats, my Renntech Tune (Stage 2 Tune) was modified even before the exhaust job, as a catless tune and my oxygen sensors are switched off for the entire time before/after the exhaust. Therefore again, the ECU tune was modified accordingly even before the exhaust was installed, oxygen sensors as well. Also pipe diameter was increased to 76 mm.

You need to data log your car while driving and do some hard accelerations so you can understand what is going on. The data provided can show why you are not making the power you should be. Those conclusions (boost issues, spark issues, fuel delivery issues, etc......) to why power is down can then lead to what is causing the underlying problem (turbo issues, bad plugs, fuel injector malfunctioning, tune, Etc....).

I have just received these AWE flap simulators. Can you please help me on the installation? Due to the fact, that my original exhaust flappers are still connected and stored in the trunk, I am not able to lock the car, leave it sitting for 5-10 minutes and then disconnect them and connect these simulators. I always will have to open the trunk to do that. Is there any way of doing this without getting a faulty code with an open trunk? I am thinking of disconnecting my battery, but I've heard there are two of them in the S63 Coupe and I have no idea where they are and if that would help at all. Any help would be greatly appreciated.

Unplug flap from wiring harness, plug in black piece to wiring harness. Throw flaps in trash. I have no idea what you are talking about with trunk and 5-10 minutes