Kickdown Problem

[merc convert]

I am new to this forum and Mercedes so here goes, 99 C250TD auto 65,000 mls.
When I kickdown hard in any gear the engine revs to 4,500rpm but does not pull. The car drives faultless otherwise in all gears and drops a gear ok when pushed. The kickdown switch is complete.

 

[kevinororke]

Hi, I've got a 2000X C220 CDI Auto. The kick-down is sluggish but activates acceleration eventually. Ie within 1 - 2 secs. This can seem like a very long time !! The revs go up right away, it just takes while to select a lower gear. The delay is most apparent when slowing down to, say, enter a roundabout but the box is still in 5th. Floor the acceletator without stopping the car and nothing happens until you are half way round the roundabout. I've stopped using kick-down in these circumstances and use the tiptronic to knock the box down a couple of gears. Regards, Kevin

 

[psmart]

Cars with Turbo Chargers have an inherent time lag. If your engine is below 2000rpm and you floor it (kickdown) it will take a second or two before the turbo winds up and the engine delivers enough torque/power to make you move. Straight diesels deliver there oomph immediately as they are generally longer stroke and higher compression ratio. The modern turbo diesels have gone to shorter strokes and less compression (needed when fitting a turbo) so they are gutless at lower revs until the turbo comes on song.

As the car gets older this could become more noticeable as things clog up, such as the air inlet (filter, intercooler, piping). Also, things such as the MAF (air mass sensor) could be going, so not letting the engine know the Turbo is on song and thus not delivering a correct fuel dosage.

First things first, ensure that your not expecting instant power, on a turbo diesel (also, same on petrol, my cosworth used to be really bad in this area, so you tended to keep high revs/low gear when boy-racering ), unless the engine is above 2000rpm and has been there a short while, your not going to get immediate response.

 

[Stevie A]

Kickdown sensor problem if no kickdown?????

I test drove a petrol 190E and when you used kickdown revs increased but it didn't go down a gear and it was a dog, so I didn't buy it.

On the good 190E I own, the kickdown works but you do get a slight burst of high revs then it drops down a gear. Maybe this is peculiar to Mercs?

Kickdown on other automatics I've owned was much smoother and instant. I would be interested to hear other people's experience of Merc kickdown.

 

[jberks]

It is true that there is a fair amount of turbo lag, but not enough to notice revs increase and no acceleration. However, there is another factor. 4500rpm is too high to be useful on a diesel. You are already well beyond the torque curve and drifting into the flat spot.
I have found this on the 270 from time to time, where you'd actually be better riding the torque curve in a higher gear than dropping a cog with the resultant drop in available rev range. As a result I tend to use kick down far less on my cdi that I did on my old V6.

 

[merc convert]

Thanks for the replies, i have found a pipe disconnected to the (what looks like an air cooler) this produced a hissing sound. On reconnecting this performance has improved. I have not fully road tested but i think the kickdown is still not dropping two gears so may still have a problem.
I will return!!!!!

 

[merc convert]

Thanks to everyone.. Seems to have done the trick re-connecting the pipe all is ok now.