Loss of Power after using Cruise Control

[assad]

E220 CDI
Has anyone else had this problem.
The cruise control works fine at all speeds but if you set to above 80mph and drive for about a minute at that speed then take it off cruise you have no power it will accelerate but very slowly like if the turbo is not working.
If you stop and turn off the ignition then restart it again its ok.

 

[jberks]

Are you sure its the cruise? How is it if you drive normally at 80?
Do you accellerate to 80 and then switch on or use the lever to accelerate?
The computer is panicking about something and often harsh acceleration will trip it if the MAS etc are on the way out. The cruise will floor it if asked to go say from 40 to 80.
In any case, you probably need the fault codes from the ECU.

 

[assad]

Loss Of Power

Hi tried driving 80-85 mph for about 3 miles without cruise control and it did the same lost power.
The car is only 9 months old.
No fault lights come up.
Assad

 

[blassberg]

Hi tried driving 80-85 mph for about 3 miles without cruise control and it did the same lost power.
The car is only 9 months old.
No fault lights come up.
Assad

do you get a max speed of 50 or 60 after that? happened to a colleagues C220

 

[assad]

Loss Of Power

No it will keep accelerating to above 80 mph but very slowly.
Put it this way if you drop down to say 50 mph and try and pick up speed, it will take ages to get back to 70 mph. You would not dare and try to overtake it would be dangerous.
Cheers Assad

 

[jberks]

Something is reporting an out of range signal so to protect against making a wrong decision, your ECU is going into get you home mode. That is why its fine after a restart. Whatever it is, can cope under 80 but not above. It could be one of a number of things, the most common being the MAS but as it's 9 months old, just drop it back to the dealer. When interrogated, the ECU should report what it isn't happy with and the dealer will simply swap out whatever sensor is playing up.
When my MAS went I didn't get a warning light either - just the symptoms you describe - it would go, but wouldn't pull the skin of a rice pudding. 0-30 in 10 secs etc.

 

[piestore]

cdi limp

HI

most common cause on newer vehicles is loss of boost pressure control, you will need the fault codes to go any further get it back to a good dealer to sort

 

[Bealo]

This happened to my CLK 320 W reg 2000 on the ride home after i bought it, i joined a motorway and accelerated hard, after i eased up i tried to overtake and there was no power. I stopped at a service station and the car was nearly stalling when it was in drive but when i put it in park the revs rose and it was fine. i turned the car off and started it again and it was fine.

What is this MAS you are talking about?

Also when it did it i couldn't use the tiptronic gearchange!!!!!

Any other ideas?

 

[jberks]

MAS or MAF or AMS (all the same thing) is the Airflow Mass Sensor. Its a device installed in the air intake with a wire that is heated electrically and judges the amount and density of the air coming into the engine by the rate the wire is cooled. The ECU then adjusts the fuel supply accordingly. The problem is that as they are in line in the airflow, even with a good air filter, some muck can get to them and they are extremely sensitive. Also, when you switch off the engine, they are heated mometarily to a very high temperature to burn off any residue. This over time with a lot of stop-start can also kill them.
The ECU allows a fixed range of readings so when they report an go out of range value, the ECU no longer trusts it and has no way to determine the air coming in and so switches to a default 'get you home' mode. At low speeds faulty ones can mis read but remain within tolerances - at high speeds with large flows, they can report out of range - hence failures at 80+. The point is that if it does mis report over 80, there is no guarantee that it is accurate at 40, potentially leading to an over rich mixture and over time killing the catalytic converter. Switch off and on and the ECU gives it another chance - hence it will run ok until it exceeds the range again.
They are a very common failure on most modern cars and show up easily on the ECU diagnostic.
In get you home mode, the gearbox may also misbehave, with no tiptronic and odd gearchanges. Basically the computer has put its bat and ball away and is no longer playing.

 

[Bealo]

Thanks jberks.

Are they expensive to replace?

 

[jberks]

Mine was around £250 plus fitting (5 min job fortunately) plus the £60 charge for the diagnostic to show it had failed in the first place. They vary in price depending on the model but I think mine was one of the more expensive ones.
They do come up on ebay and the non dealer parts guys may do a better deal too.

 

[brent141]

My E220 has just done the same today. I couldn't get it to kick-down once it was in top gear. At one stage on the m-way I had to manually change down to 4th and when I put it back into "D" there was a slight resonance from what appeared to be under the car. I still had the problem with the lack of kick-down though until I had to stop at a junction. After that (I did put my foot down to pull away) - it appeared to be fine. Any ideas?