SL55/63/65/R230 AMG: New TCU choice for SL55 feels like game-changer
Newbie
Joined: Jun 2025
Posts: 3
Likes: 0
2003 SL55
Old thread I know, but was happy to find it and use the info to order a stage 1 MK Ultra TCU for my 2003. I’ve had my SL55 for a few weeks now and plan to add split cooling, an extra heat exchanger and 76mm pulley once they arrive from VRP. I was going to order the VRP TCU as well, but liked the idea of getting to keep my original TCU, A mode and MK’s much better price.
I don’t have STAR so can’t reset adaptations. I installed the new TCU and went to put the 50-100 miles down to have it readapt itself. I noticed 4 times while driving the first 20 miles it felt like I lost input from the super charger. No lights but almost like I was in limp mode. Then after a few minute of calming down my driving my full power under throttle was back. I was thinking maybe heat soak since no split cooling installed yet, but the car has never done that before even when driven hard. It has only happened since I put the MK ultra in and happened in S C and A mode (I tried them all to see if 1 would correct it).
I read somewhere else a faulty TCU can lead to supercharger bypass or the ECU otherwise taking power out. For the folks that didn’t use STAR and had to put miles on to readapt, did you also experience this? Trying to determine if this is part of the adaptation process, I got a bad TCU from MK Ultra or maybe something else. Crisper shifts leading to quicker hear soak that didn’t happen before? I’ve considered swapping back to my stock TCU to see if the issue goes away, but wasn’t sure if it was part of the adaptation process and will go away after I put more miles on it not.
This is my 1st MBZ and supercharged vehicle so still learning how everything works. Any advice is extremely appreciated.
I don’t have STAR so can’t reset adaptations. I installed the new TCU and went to put the 50-100 miles down to have it readapt itself. I noticed 4 times while driving the first 20 miles it felt like I lost input from the super charger. No lights but almost like I was in limp mode. Then after a few minute of calming down my driving my full power under throttle was back. I was thinking maybe heat soak since no split cooling installed yet, but the car has never done that before even when driven hard. It has only happened since I put the MK ultra in and happened in S C and A mode (I tried them all to see if 1 would correct it).
I read somewhere else a faulty TCU can lead to supercharger bypass or the ECU otherwise taking power out. For the folks that didn’t use STAR and had to put miles on to readapt, did you also experience this? Trying to determine if this is part of the adaptation process, I got a bad TCU from MK Ultra or maybe something else. Crisper shifts leading to quicker hear soak that didn’t happen before? I’ve considered swapping back to my stock TCU to see if the issue goes away, but wasn’t sure if it was part of the adaptation process and will go away after I put more miles on it not.
This is my 1st MBZ and supercharged vehicle so still learning how everything works. Any advice is extremely appreciated.
Junior Member
Joined: Mar 2013
Posts: 74
Likes: 6
From: Southern NH
2003 SL55 AMG
Hi, I did the same route 2 years ago. I had a couple go arounds with Troy until he got me the right tune. It works well, but the first to second gear shift is pretty jolting at any rpm. If you have problems with your car losing power after flooring it, you could need a new throttle pedal. I had to replace mine and that cured the problem. About $200 from FCP Euro, the best place to buy anything.
Super Member
Joined: Jul 2010
Posts: 955
Likes: 127
From: Kansas
2003 E55, 2003 SL55, 2014 CLS63, 2018 q50 Redsport, 1968 Camaro SS, 1999 Trans am Firehawk
Old thread I know, but was happy to find it and use the info to order a stage 1 MK Ultra TCU for my 2003. I’ve had my SL55 for a few weeks now and plan to add split cooling, an extra heat exchanger and 76mm pulley once they arrive from VRP. I was going to order the VRP TCU as well, but liked the idea of getting to keep my original TCU, A mode and MK’s much better price.
I don’t have STAR so can’t reset adaptations. I installed the new TCU and went to put the 50-100 miles down to have it readapt itself. I noticed 4 times while driving the first 20 miles it felt like I lost input from the super charger. No lights but almost like I was in limp mode. Then after a few minute of calming down my driving my full power under throttle was back. I was thinking maybe heat soak since no split cooling installed yet, but the car has never done that before even when driven hard. It has only happened since I put the MK ultra in and happened in S C and A mode (I tried them all to see if 1 would correct it).
I read somewhere else a faulty TCU can lead to supercharger bypass or the ECU otherwise taking power out. For the folks that didn’t use STAR and had to put miles on to readapt, did you also experience this? Trying to determine if this is part of the adaptation process, I got a bad TCU from MK Ultra or maybe something else. Crisper shifts leading to quicker hear soak that didn’t happen before? I’ve considered swapping back to my stock TCU to see if the issue goes away, but wasn’t sure if it was part of the adaptation process and will go away after I put more miles on it not.
This is my 1st MBZ and supercharged vehicle so still learning how everything works. Any advice is extremely appreciated.
I don’t have STAR so can’t reset adaptations. I installed the new TCU and went to put the 50-100 miles down to have it readapt itself. I noticed 4 times while driving the first 20 miles it felt like I lost input from the super charger. No lights but almost like I was in limp mode. Then after a few minute of calming down my driving my full power under throttle was back. I was thinking maybe heat soak since no split cooling installed yet, but the car has never done that before even when driven hard. It has only happened since I put the MK ultra in and happened in S C and A mode (I tried them all to see if 1 would correct it).
I read somewhere else a faulty TCU can lead to supercharger bypass or the ECU otherwise taking power out. For the folks that didn’t use STAR and had to put miles on to readapt, did you also experience this? Trying to determine if this is part of the adaptation process, I got a bad TCU from MK Ultra or maybe something else. Crisper shifts leading to quicker hear soak that didn’t happen before? I’ve considered swapping back to my stock TCU to see if the issue goes away, but wasn’t sure if it was part of the adaptation process and will go away after I put more miles on it not.
This is my 1st MBZ and supercharged vehicle so still learning how everything works. Any advice is extremely appreciated.
Newbie
Joined: Jun 2025
Posts: 3
Likes: 0
2003 SL55
I have not yet opened the transmission. I was going to wait until it needed a fluid and filter change but I guess I could do that early. I assume it is brown tops as the PO didn’t do any mods and it’s an early 2003 (March). When giving specs for the tune I provided my VIN and was given the tune for brown tops (Noted in my tune sheet).
Everything was fine once I swapped back to my stock TCU and I’ve already been shipped a replacement stage 1 MK Ultra (great customer service, resounding to me on a Sunday and immediately providing troubleshooting advice/ solutions). If the new one still acts up I think dropping the pan and swapping to blue tops is my next step. Was hopping to avoid dropping that $450 in solenoids. When I was looking into VRP’s TCU tune (before learning about MK Ultra) they let me know for a 76mm pulley that is street/ twisty road focused vs. track focused to start with a TCU tune as it would probably be enough vs. doing a valve body, blue tops etc.
Also in case it helps someone in the future, I learned if you don’t use STAR to readapt you should drive lightly, not aggressively, in the 1st 50-100 miles after putting the new TCU in. This allows it to learn overlaps and clutch clearances. I thought it was just learning your driving style, but I guess not.
Junior Member
Joined: May 2016
Posts: 52
Likes: 3
From: Alamagordo NM
2007 sl55
TCU
I am guessing that TCU is an acronym for transmission control unit? Can you guys confirm that this is different and separate from an engine tune? I have a 2007 SL 55 . does this TCU eliminate the speed limiter? Not even sure if my car has a speed limiter haven’t had it over 175. I think that the car may be limited to 185.
Newbie
Joined: Jun 2025
Posts: 3
Likes: 0
2003 SL55
Yes TCU tune is different from an engine tune, its transmission specific. Shouldn’t have anything to do with removing top speed limitations, it is more to improve shift points and tighten up some of the slop from what I understand.
Super Member
Joined: Sep 2021
Posts: 537
Likes: 116
From: Ann Arbor, MI
2004 SL600
Appreciate the advice.
I have not yet opened the transmission. I was going to wait until it needed a fluid and filter change but I guess I could do that early. I assume it is brown tops as the PO didn’t do any mods and it’s an early 2003 (March). When giving specs for the tune I provided my VIN and was given the tune for brown tops (Noted in my tune sheet).
Everything was fine once I swapped back to my stock TCU and I’ve already been shipped a replacement stage 1 MK Ultra (great customer service, resounding to me on a Sunday and immediately providing troubleshooting advice/ solutions). If the new one still acts up I think dropping the pan and swapping to blue tops is my next step. Was hopping to avoid dropping that $450 in solenoids. When I was looking into VRP’s TCU tune (before learning about MK Ultra) they let me know for a 76mm pulley that is street/ twisty road focused vs. track focused to start with a TCU tune as it would probably be enough vs. doing a valve body, blue tops etc.
Also in case it helps someone in the future, I learned if you don’t use STAR to readapt you should drive lightly, not aggressively, in the 1st 50-100 miles after putting the new TCU in. This allows it to learn overlaps and clutch clearances. I thought it was just learning your driving style, but I guess not.
I have not yet opened the transmission. I was going to wait until it needed a fluid and filter change but I guess I could do that early. I assume it is brown tops as the PO didn’t do any mods and it’s an early 2003 (March). When giving specs for the tune I provided my VIN and was given the tune for brown tops (Noted in my tune sheet).
Everything was fine once I swapped back to my stock TCU and I’ve already been shipped a replacement stage 1 MK Ultra (great customer service, resounding to me on a Sunday and immediately providing troubleshooting advice/ solutions). If the new one still acts up I think dropping the pan and swapping to blue tops is my next step. Was hopping to avoid dropping that $450 in solenoids. When I was looking into VRP’s TCU tune (before learning about MK Ultra) they let me know for a 76mm pulley that is street/ twisty road focused vs. track focused to start with a TCU tune as it would probably be enough vs. doing a valve body, blue tops etc.
Also in case it helps someone in the future, I learned if you don’t use STAR to readapt you should drive lightly, not aggressively, in the 1st 50-100 miles after putting the new TCU in. This allows it to learn overlaps and clutch clearances. I thought it was just learning your driving style, but I guess not.
IMHO, anyone opening the trans and removing the valve body should replace the troublesome "conductor plate". A complete kit is just $225 from FCP Euro with a German made plate. (Cheaper ones are under $100 on Amazon.)
