musicaljoe

Hi all, wondering if the knowledgeable bods on here can give me a bit of advice...

my SL55 has always seemed to me to have an issue with a sort of delay before accelerating. I've read a lot about the 2002 SL55 auto box being a little sluggish, but I'm convinced this is a 'Problem' rather than a 'characteristic'.

most obvious issue is if I'm driving along at 30mph for a mile or two, when it's time to put my foot down, in the worst case scenarios there's a 3-4 second delay before ANYTHING happens. Literally it's like you haven't even pressed the pedal.

But also, it always seems to have a big delay when I want power. Perhaps the best way I can explain it is... whatever speed I'm at, i want to go faster and press the throttle. I'll be at (say) 2000rpm. For a second or two, the car tries to accelerate n whatever gear it is in. But then it realises that it can't accelerate very fast in that gear (prob 4 or 5) so drops to 3, or perhaps 2. When it's gone to the right gear, everything is fine. It's that big delay before it gets itself into the right gear.

in manual mode, I don't have the problem, because I'm choosing to go down a gear or two with the switches. So it doesn't seem like a problem with the gearbox itself.

I was trying to work out if there was maybe a sensor problem... and this COuLD be it... let's say I'm in 4th in 'Manual mode' and doing 30-40mph, if I put my foot down (without changing gear) there's very very slow build up of speed. But that's at maybe 1500/2000 revs, so maybe that's normal. Or maybe it's not giving the right air mix at low revs... not sure!

i then read a post about the throttle position sensor, and think this might actually be it. Someone mentioned that if this isn't working properly, the car can get mixed messages about what it should be doing.... that would explain both the 'nothing at all happening' problem AND the 'wrong gear' feeling..

so, any advice would be welcomed! Thanks in advance for your advice.

amok55amg

you better go for a diagnostic ........ it could be many things.

dafi129

Gearbox issue , not engine . Box is slow to kick down . I have the same on my 2002 . Change to Sport mode or go manual .
In W mode , gearbox is really slow . Car tends to keep the same higher gear unless you really press down .
I've had this for 3 years , since I owned the car .

Nor Cal SL55

You may want to try a reset...

https://mbworld.org/forums/w211-amg/...set-works.html

musicaljoe

Thanks to everyone who helped. In case anyone has similar symptoms and comes across this thread in the future, the reason was a bad TCU which had been damaged by oil creeping into it. cleaning it out didn't help, but replacing it with a second hand TCU from another SL55 fixed the issue.

latemodel21

make sure you replace the transmission electrical connector adapter/seal (oddly called "pilot bushing" MBZ pn A2035400253). That is the source of the fluid that wrecked your TCU. Another preventative measure you may want to consider is to rotate your TCU 90° (so that any ATF that makes it that far wont pool in the TCU) . If you are thinking you may want to do it, here is a link to another post in which I included pics of my re-positioned TCU https://mbworld.org/forums/sl55-amg-...ml#post6128428

Cheers,
Chris

musicaljoe

I seem to remember my chap telling me he'd fitted a seal which prevents the leakage when he serviced the gearbox - if that's the one you're talking about? Interesting idea to rotate the unit - it's a really bad design, isn't it?!!

Actually, when I put the newer TCU in, the one thing that *stopped* working were my gear change buttons on the steering wheel. We know we can flash the TCU from STAR, but the choices don't make it clear which code numbers are for which models. Do you happen to know if there's an easy way to tell, or a reference somewhere online that can point us to which one to use if you have certain upgrades (like the tappy buttons)?

Thanks again for the advice!

latemodel21

The "pilot bushing" (connector seal) is a common maintenance item, so I suspect that IT IS what your service guy was referring to (having replaced).

there is year specific "varient coding" that you would apply to your TCU (to choose E55 vs SL55, etc) you would want to plug your old tcu back in to read it and then try changing it on your new tcu (code will be like .... "AM72" ) this will work if you have used the same TCU (same part number) .... if you have not used the same TCU, this may not apply. As an example, when I upgraded my 2003SL55 to use a 2004 valvebody (with blue tops), I also switched to a 2004 TCU (along with being correct for the 2004 valve body, the 2004 was an upgrade because it allows the "flappy paddles" to work in all modes, unlike the 2003 TCU which only allows paddles in "manual" mode). So, the 2004 TCU worked, but apparently was coded for a 2004 e55 (would give a trans gear miss-match failure as soon as you started driving) so I had to change it to 2004 sl55 coding which was NOT the same as 2003 sl55 coding (coding needed to be different from the 2003 because it was a different Part number TCU )

I don't recall you mentioning the year of your SL55. 2003-2006 (230474) handled the "flappy paddle" functionality through the floor shifter (this was the "analog" configuration that used the shift buttons in series) . My understanding is that the presence of flappy paddles must be indicated (chosen) AT THE TIME that the floor shifter is MARRIED to the car. Is it possible that your floor shifter was replaced or somehow "VIRGINALIZED" and subsequently re-married? If you poke around in star (look in "switches" of EGS IIRC) you should be able to test the buttons, but my understanding is that you cannot turn this function off and on (once the shifter is married)

the rest of the SL55's ....
Late 2006 through 2008 SL55 (230472) used a different strategy for paddles (it used the same strategy as 2005 and newer R230 with option 428). In this configuration the (now digital) paddles are voltage coded in the N135 module (under airbag) and then fed into the N80 (jacket tube module) where it is then added to the CANBUS .... in this configuration option 428 can be added in order to make the paddles work.

which year (version) of sl55 do you have? I could give you some more specific troubleshooting steps if I knew.

Chris