pullaway in auto diesel

[Andy Beatty]

ive had diesels and have had powerful automatic petrol cars but not automatic diesel.

there seems to be a short delay when you first hit the go pedal from stationary or should it be stationery?? but acceleration is great when already moving. is this normal on merc diesel auto on come to that any auto diesel

ta very much

Andy

My cars

1997 R E300 Td Estate Silver now without blacked out windows

1991 H Rolls Royce Silver Spur II dark metalic blue now with scratch on wing.

 

[kid-jensen]

Andy,

Do you get the same delay when booting it in neutral? If you do it's an engine response problem.

If the engine responds quickly in neutral but there's a delay before you actually get any movement, you could have something simple like low/high fluid level. Make sure you check it exactly as per the manual.

If the last fluid change is unknown, change it anyway.

As a last resort, you caould always stall the converter..........

 

[dieselman]

There is a delay when first pulling away. It is due to the torque converter winding up before transferring drive. You get used to it.

I don't know why but the petrol cars seem to have a higher degree of drive through the converter when at idle so the torque effect is more instant.

 

[Andy Beatty]

Thank you

 

[andy_k]

I was always warned never to "boot" or rev an auto when it's sitting in neutral - I seem to remember dire warnings about destroying torque convertors.

Andy

 

[dieselman]

Andy

A bit of an old wifes tale I think. The whole converter will be turning together anyway because the gearbox is in Neutural.

 

[jberks]

I would expect a bit of a delay on an 300TD. I find with most diesels that turbo lag is all. Whilst you can get round it with a manual, its harder with an auto. Newer CDIs are better but the 'older' diesels were a bit jecke and hyde, either asthmatic or ferraris depending on the revs. My Wifes Jeep is similar, quite lively once going but painful if you don't get the revs up before releasing the clutch.

 

[Rory]

I was always warned never to "boot" or rev an auto when it's sitting in neutral - I seem to remember dire warnings about destroying torque convertors.

Andy

It used to be said that you can destroy the engine (by throwing a rod) because there's so little load on it. I never really understood why an auto was different from a manual in this respect, though - would the drag of the manual gearbox make that much difference?

 

[Rory]

there seems to be a short delay when you first hit the go pedal from stationary or should it be stationery??

Some are quite bad - Volvo XC90 (which I've never driven) is noted for having a very sleepy stepoff. I had a Mondeo TDCi auto for a few days a couple of years ago (so it might be better now) and that was terrible. Fast flowing roundabouts where just scary - I ended up spooling up the engine and holding it on the footbrake. It then took off so fast that I was glad it was an auto so I could hold the wheel with both hands!!

It was the first thing I checked when I test drove a (brand-new) 05 C220, and the 54 reg C270 that I eventually bought is perhaps marginally less sharp, which is maybe because of the bigger engine, or it could be my imagination.

My gearbox has C and S settings - I always drive in S (in C it starts in second, unless you set off quickly then it 'thunks' as it drops to first, which I find annoying).

 

[niva441]

The problem with revving the engine in neutral is that your putting energy into the gearbox that doesn't have anywhere to go, so is converted to heat. This has been known to cause problems for transmission oil and seals.

 

[raycul]

Quite an interesting thread.

I bought my wife a 300TD estate 1998 model.

I took it back to Mercedes because I felt there was too much revving required for the pickup. ie 12 rpm to pull away slowly and in reverse up to 1500 rpm! Mercedes say this is normal! From what you all say it seems to be so.

I drive a BMW and the auto box is moving the car as soon as you touch the throttle. My wife finds the Mercedes a lovely car to drive apart from the take off on the auto.

Can this be modified?

 

[230K]

Hi Raycul

Are you sure it is in S mode on the gearbox, the switch between W&S sometimes sticks in the W setting.
Check by having the car running in D and W and stopped. Switch to S and you should feel a v slight jerk. If nothing is felt it is most likely the car is stuck in W.

230K

 

[Guy Greenwell]

Hi andy.
Yes my C250 Turbodiesel has the same delay which you speak of. I think it is because the injector pump is not directly operated by a cable from the accelerator as on older diesels, instead the pump is controlled electrically through the management system.
I have always driven autos with my left foot for brake and right for accelerator and found that if I keep my left foot on the brake whilst opening the throttle a little for a rapid departure, as I can do in my old Jaguar Sovereign the engine does not respond until the footbrake is released.
Hope this is of help,
Guy

 

[Zanimat]

At last! Another two-footed auto driver! I thought I was alone - all my friends & acquaintances think I'm barmy for using both feet. It's something I've always done; the way I see it is that there are 2 pedals & I have 2 feet - one for each! I'm sure I have greater control over the car, particularly when manouevering in tight spaces or when needing a sharp getaway - and my 300D does have the lag which started this thread. It also goes some way to outwitting the Merc's weird parking brake arrangement.

 

[jberks]

Two footed auto driving is a contentious point. My only real critisism is that we can easily spot most drivers who do this - they're the ones who's brake lights come on whilst accelerating and we're never quite sure whether they are slowing down or not. Causes some hairy moments for the poor buggers behind. Its true - two pedals and two feet, but IMHO you only actually need one at a time!

The car wasn't designed to be revved with the brake on and whilst an occasional use of this technique is probably fine and sometimes useful, (I have done it myself) making a habbit of it could damage the gearbox, plus I'm not sure what an SBC equipped Merc would make of it.

Bottom line is that my car behaves fine without the need for such techniques, sure its more sluggish than a manual off the line, but I simply compensate by pre-empting the need for a fast take off by hitting the throttle a moment earlier. Also I find that if I don't fully floor the pedal, it doesn't muck about dropping into 1st and I get a quicker overall take off.

 

[Guy Greenwell]

Hi Andy,
I tried to send this to you the other day, but went wrong somewhwre.
I have a C250 Turbodiesel auto which I bought about 6 weeks ago and it too has a delay on pressing the accelerator.
On older cars the injector pump was controlled direly by a bowden cable from the accelerator.
On this model Merc.I believe this to be caused by the injector pump being controlled through the engine management system.On this model, the accelerator pedal is connected to a potentiometer which tells the management system how far down you have pressed it. the computer then opens the pump up accordingly,it can also close the pump down in certain instability or lack of traction conditions.
I always drive autos using my left foot for the brake, on my Jaguar with manual throttle control this allows a few revs to be built up against the torque converter for a rapid departure if required. On the mercedes this is not possible, in fact it seems to make it slower, as the accelerator is rendered almost innefective until the footbrake is released. I presume this is tied up with the electronic stability ABS and traction control system, ( oh why cant we keep things simple and easy to fix)
Hope this makes sense.
Regards
Guy

 

[raycul]

Hi Raycul

Are you sure it is in S mode on the gearbox, the switch between W&S sometimes sticks in the W setting.
Check by having the car running in D and W and stopped. Switch to S and you should feel a v slight jerk. If nothing is felt it is most likely the car is stuck in W.

230K

Hi,
Sorry for the delay in replying.

Yes I have tried moving the switch and there is no jerk (I bought myself an S320 CDI & That did) so is it just the switch or do I need to delve deeper into this?

Thanks for your help!

Ray

 

[230K]

Raycul

The switch is usually ok it is little bits of dirt and dust that jam a little rod that pushes down on the switch.
Remove the plastic surround around the selector, i think from memory peel off the PDRD4321 sticker and then click out the the w/s switch and be careful a little spring should pop up and out, the w/s switch actually pushes a little plastic rod that operates the switch deeper down in this little rod gets fouled up and keeps the gearbox in W.

Mine has done it twice, 5-10 min job once you have done it once.

Goodluck

230K

 

[raycul]

Raycul

The switch is usually ok it is little bits of dirt and dust that jam a little rod that pushes down on the switch.
Remove the plastic surround around the selector, i think from memory peel off the PDRD4321 sticker and then click out the the w/s switch and be careful a little spring should pop up and out, the w/s switch actually pushes a little plastic rod that operates the switch deeper down in this little rod gets fouled up and keeps the gearbox in W.

Mine has done it twice, 5-10 min job once you have done it once.

Goodluck

230K

You were so Right!!!!! :-D

Push rod was stuck down. Bit of silicone grease and it's a right as rain!

Many Many thanks for your advice.

I owe you a drink. If your ever in Calais shopping let me know by email I'll make sure there's a bottle of champagne waiting for you where I work! (I am general Manager of a wine outlet over there by the way!) ;-)

Something so easy that Mercedes would probably have charged a couple of hundred quid for and said Oh we have to check this that and the other.

Cheers

Ray

 

[230K]

Ray

Great, glad you got it sorted, there is nothing to it once you have done it once it will be easy to do again. Did you take it apart or spray in silicon, if i had the silicon spray it would have been handier.
Is there much difference in the way the car drives should feel a lot nippier.

Will be passing through Calais Friday morning 8th July and on return staying in Guines on Thursday 21st departing out of Calais on Friday morning 10am ferry.
Myself, wife and the four kids on our summer hols in the E300TD Estate.
They have a few vices but great cars.

Reading back up through the thread did you try MB to sort this and they were unable?

Anyway cheers, only too glad to help,

230K