W203 cruise only working till 65mph

[newt888]

Hi ere
I have developed a fault with my 2002 c32 , today on a journey I tried to activate the cruise control to on at about 80mph , flicked the switch up took my foot off accelerator and the car slowed down !
Tried it a couple more times no luck
Tried it at lower speeds till I reached 60 mph and it flicked on no probs!
I then used the stalk to accelerate and as soon as it went over 65 it switched of and the car slowed down, a couple of times it accelerated through 65 using the stalk but as soon as stalk was released it slowed down again, just to add cruise works perfectly up to and including 64 mph
Any ideas?
Will tyres sizes make a difference as I have just fitted a set of staggered 18s and there is a slightly more visible difference in wheel diameter compared to the staggered AMG 17s which I might add are not the same diameter front to back

 

[Privatedoc]

is the limiter on or faulty?....(push cruise stalk in)

 

[0ptic]

This is just a maybe OK. I wonder if the ECU is detecting a big enough speed difference between wheels (front to back??) from the ABS sensors to think there may be wheel spin etc. Pretty cleaver electronics these days and now everything goes through the ECU just a little bit more programming.

Just a thought.

 

[chitaxmoto]

similar problems were discussed a few years back, think it was brakes/abs that was the fault. search the forum

 

[newt888]

is the limiter on or faulty?....(push cruise stalk in)

No limiter works just fine and was off

 

[newt888]

This is just a maybe OK. I wonder if the ECU is detecting a big enough speed difference between wheels (front to back??) from the ABS sensors to think there may be wheel spin etc. Pretty cleaver electronics these days and now everything goes through the ECU just a little bit more programming.

Just a thought.

That's what I'm thinking although the stock AMG setup is different front to back I may be running a bigger difference now

Can anyone confirm that it needs to read front and back and "accept " a certain difference

 

[andy27168]

Hi,
Wrong tyres can cause this problem, as a rule of thumb if you go up a wheel size you need to decrease the tyre profile, on my C43/55 I have the staggered set up but 17"s with 40 and 45 profile tyres, if i were to go to 18"s i would have to decrease the profiles to 35 and 40.

 

[BTB 500]

Put the wheel & tyre dimensions (front & back) into the 'tyre size calculator' on this page:

Car Bibles : The Wheel and Tyre Bible Page 3 of 4

That will give you the actual rolling radius for each, and the percentage difference. You might also want to compare with the stock setup (here: http://www.alloywheelsdirect.net/information/fitting_chart/mercedes-benz) because regardless of CC issues if you are running non-standard sizes then the speedometer may be over or under reading.