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Hello guys, I've noticed that my car on acceleration is not getting full boost gauge to max. Even on full throttle it's like 3/4 of it. Xentry checked for errors and nothing was found. Can it be bad fuel quality or what to look for? Attached photo where you can see max boost i've getting. Thanks
Your car is most likely in limp mode. If you bring up the engine data screen what does the horsepower scale say? If it's less than 500 then it's in limp mode. Can happen if there was an electric failure. Need to take it in to get checked and taken out of limp mode.
Checked for errors and didn't get any. I have non S version so it will be lower than 500. And in my car there is kW instead of hp. On full throttle boost gauge totally live it's own life and blinking lower and higher. Can attach video of acceleration if it can help
Checked for errors and didn't get any. I have non S version so it will be lower than 500. And in my car there is kW instead of hp. On full throttle boost gauge totally live it's own life and blinking lower and higher. Can attach video of acceleration if it can help
If it's in limp mode then the power gauge scale on the engine data screen will max out at about half of the rated power. I see you had it up in that video, but it was too far away. Pretty easy to tell. It does look like you are way down on power. From that video it took about 8 seconds from 0-100kph. Despite loosing traction for a moment there and the TC cutting power that's quite slow even for the non-S.
This is like CPC and ECU tuning related, even if its stock.
We can help you datalog it pretty easily. If you found no codes stored in any of the modules, it can be limiting power via CPC and ECU.
If it were exhaust flaps and limp mode associated with that, the car would be very slow. Much slower. Not to mention it is hitting the advertised amount of torque on the dash display.
Spark plugs and coils wouldn't do this. You would feel hesitation and hear them in the tone of the car.
Turbos maybe which is why you should datalog it. If the demand from the ECU exceeds what the actual boost is, then you have some kind of mechanical issue like turbos, or a boost leak of some sort. If this were the case however, the car would throw codes for underboost condition. This is why we think its related to ECU and CPC tuning.
From reading similar threads all i've found to look at spark plugs, coils, turbos, exhaust valves and many other reasons can cause this.....
*****Yes the above is true but a decent mechanic or person familiar with these as well as other more modern turbocharged cars will narrow down the problem very quickly. If it doesn't seem to be a sensor issue, or the car pulling major timing due to knock or pre-ignition - I'd make sure the car has decent gas in it, and then check mechanical issues like wastegate operation, or make sure one of the turbo inlet hoses are not cracked, or the evaporator canister purge solenoids not working, etc.. If you have the performance AMG exhaust, check the valves for proper operation or if they are hung up, etc..
Of course, checking the condition of the spark plugs can tell a lot about how well or not well the motor itself is running, etc.. A decent scan tool with live data and recording can allow one to analyze parameters well beyond just looking at the turbo boost gauge. Hopefully the water and transmission temps are normal and not running too high, etc.. and you do not have a coolant leak through the auxiliary heat exchangers from a stone cracking them, etc..
How long has this problem been going on and was the power loss sudden or gradual over time, etc..?
After looking in pipes with pressing exhaust button seems like everything works fine. In stopped engine they are fully open and when it starts they went fully closed
UPD: After visiting one of good mb services they told that none errors were found and if there errors with turbo, turbo pipes, spark plugs or exhaust valves its always show with error. They told me go to dealer for updating engine and transmission software. Do you think it have sense? Today tested again acceleration and if 2 days ago i got 3/4 of boost indication now i have like half of all boost indicator. And 100-200 takes 11s on good fuel
UPD: After visiting one of good mb services they told that none errors were found and if there errors with turbo, turbo pipes, spark plugs or exhaust valves its always show with error. They told me go to dealer for updating engine and transmission software. Do you think it have sense? Today tested again acceleration and if 2 days ago i got 3/4 of boost indication now i have like half of all boost indicator. And 100-200 takes 11s on good fuel
I know this thread is old but did you manage to fix the issue as I have exactly same behaviour 3/4 of the boost is showing on full throttle and I spot this after 1 month after MB updated my ECU and TCU (no warranty anymore) so not sure what to do to fix that..
Definitely sounds like you're in Limp-Mode..I had the same problem, once the code was cleared I was back in business with FULL boost.
Have a tech download your datalog to confirm.
Definitely sounds like you're in Limp-Mode..I had the same problem, once the code was cleared I was back in business with FULL boost.
Have a tech download your datalog to confirm.
GL
His video did show that it hit full boost for a brief second but not at high RPMs, or maybe I am mistaken.
Definitely sounds like you're in Limp-Mode..I had the same problem, once the code was cleared I was back in business with FULL boost.
Have a tech download your datalog to confirm.
GL
Last week was check for any errors and none, is this limp mode will record an error code..?
Last week was check for any errors and none, is this limp mode will record an error code..?
Tomorrow will go check live data while driving
In my case limp-mode did not throw a CEL but when I downloaded the data log you could see the limp mode error in the file..So my tech cleared it and disabled my exhaust valves while he was in my ECU to eliminate any further limp mode issues..I had my rear mufflers removed, which is what caused the Limp mode.
I'm having the same issue and I don't see any check engine light either. When its in engine monitor, its says 500hp and will go there at the higher gears but boost is never full. it fluctuates. Ive took of the diverter hoses off of the intake box to see if i hear them working and when I rev I get nothing. I got the car with catless downpipes so I don't know what tune is on it. can it still be in a soft limp mode? and if so how can i get it out?
Last edited by Junyaking; Mar 10, 2026 at 07:45 PM.
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C63 not getting full boost
