PERIDOT

I have never owned a new automatic transmission car before (ML 320 CDI).
Why am I unable to move off
INSTANTLY from standstill after shifting from N to D,there is a 'Def lag' effect on the accelerater pedal.
Has anyone else experienced this?:

dgiturbo

Is the lag you refer to the time for the transmission to engage when you put it in D, (that should be near instant) or is it that when in D and you step on the accelerator, there is a time to launch from a standstill?

If you refer to the later, launch time, you have a turbocharged diesel, and there will be a half second or so lag before the full 400 foot pounds of torque slams you back in your seat.

Sounds like a normal thing that you will get used to. Check your dealer if worried.

Enjoy the new ride!!! Mileage gets better with age.

tarponbeach

My CDI takes a second to engage from park to drive, but I think this normal, as the transmission selector is electronic, with no mechanical connection between the selector & the transmission.

Once in drive, there will always be a short delay if you stomp on the accelerator, as the turbo spools up.

MB Dave

welcome to the turbo world and what you are expriencing is tubo lag, a turbo runs on exhaust gases from the engine. the turbo is like a fan, so the more exhaust gases are flowing the faster it will spin it and when you are not accelarating the turbo spins but not enough to make extra power it ionizes the air and that helps too.
theyre is a lot more to this i just dont feel like typing up a a book right now

a bit exagarated video
http://www.youtube.com/watch?v=66ZH6kVKYTw

not so much exagarated its just the turbo is fairly sized on the ml320 but a 35r like on this v dub is huge

tarponbeach

BMW has addressed this on the 335 gas engine, by using two smaller turbos (1 each for 3 cylinders), but they have also had some heat related problems with this setup. The BMW Diesels due in the fall also have twin turbos. M-B however, has a lot more experience building Diesel engines, so from a durability standpoint, I'd put my money on M-B.

ima55r2

I had the same hesitation on my GL...the KD-Box cured it.

dgiturbo

...Was the KD box hard to install? What were your gains in hp? Any fuel mileage difference compared with normal driving?

ima55r2

There is one wiring connection to unhook and then connect to the kd and then plug the kd into the car. It takes a minute longer to take off the engine cover.

Haven't done a dyno so the 25% gains to hp and also torque are just claims so far...the car does feel stronger though.

As for mileage, I won't know until my next road trip. If the cdi takes a lot of miles to fully break-in as stated elsewhere, then increased mileage claims by customers might be more due to break-in than kd-box efficiency.

MB Dave

for sure, a 1992 e300td can go for around even 7-8k bmw stole audi's idea from the s4 2.7T

ima55r2

Engaging from park to drive is one thing, but with foot on the brake in drive, then stepping on the gas and having the hesitation was very annoying, probably due to fuel delivery programming. The turbo lag in drive while moving still exists but since the KD is supposed to adjust the fuel flow, my GL takes off now immediately from a stop and pulls harder than before.

lkchris

It's not turbo lag.

There are instances in my GL when pressing accel pedal does nothing.

Tejas

My Ml 320cdi has a lag from a standing start. I hear the engine spin up and then the transmission engages.

I think this is normal for the Diesel's, my old 97 E-class Diesel did the same thing.

The lag can be fun when you are trying to turn left across traffic when you step on it and it don't go! I've found if you keep creeping forward before hitting the accelerator, there is no pause or lag.

DUTCH

Come to a quick and complete stop at a stop sign and try to take off immediately just as soon as you've stopped.

LAG! Delay.

I don't care what you call it. It's there and it can be frightening; because the truck just won't move for a second or two.

dgiturbo

I have felt this, but had chalked it up to the diesel thing as my 2004 diesel Dodge Ram did the same. Once it moves, it will PULL HARD though. Maybe Mercedes could reprogram the ECU for better throttle response?
Or I may just do the KD box route.

sydunipete

I've got the same sensation with my 06 ML500. It's intermittent and very noticeable when it occurs.

lkchris

That's exactly what my GL does.

Can't be sure about these things, but I think it started with the replacement crankshaft position sensor.

tarponbeach

Don't forget that these vehicles are drive by wire, and not a mechanical connection to the throttle & pedal, like days of old. Every drive by wire car that I've ever driven has a slight delay

DUTCH

My G500 is drive by wire and does not have this problem.

DUTCH

Mine has been doing it since new. 35K miles on it now.

I can still very vividly remember making a quick full stop at an intersection and trying to take off to beat an oncoming car. If that oncoming car hadn't applied his brakes hard, I would not have beat it. Just about had to go home to change my knickers. Been wary of those stop and quick start situations ever since.

lkchris

Can't argue that.

Is this part of the still-to-come transmission fix you've posted about or is it something else?

red00lght

My ML500 has instant thrust...sometimes more than asked for by a slight jab of the pedal. However, my wife's Audi A4 1.8turbo CVT had a serious problem with initial lag. I think it was partly the CVT to blame as well as the turbo. You could floor it and it felt like you could count to 3 before anything happened. Very scary and sometimes dangerous.

DUTCH

I don't know, but I doubt if it's transmission related. More like engine management is what I think; although they're almost certainly interrelated.

JDN34

I believe this is called BTL = Brake Throttle Lag

It happens when one brakes hard or come to a complete stop and get on the gas right away. Only happens on automatic transmissions. It almost has no cure and happens with many makes and models.

If my memory serves me correct, this implementation of BTL is intentional since there was a case against an automaker (Audi?) where an old lady accidentally hit the throttle after she hit the brake very hard in the 80s. After the case, many automakers adapt this mechanism to prevent this from happening and implemented as a "safty feature".. This particular lag varies as different automakers have a different interpretation as to how much lag is considered "safe"!

It's more noticeable especially on newer cars with turbo since turbo has a non-linear accelaration. It more dangerous for turbo cars/trucks when the boost is built up for release at a lower rpm. So BTL will be longer to prevent accedents from happening. Longer BTL + Turbo lag -> Very noticeable!

This is very well documented on the Web. Search BTL or Brake Throttle Lag

However, some aftermarket crowd came out with a "black box" to bypass this mechanism (KD Box?)

JDN

DUTCH

Perhaps so; but by G500 (auto tranny, drive by wire) doesn't do it at all. This 320CDI engine is downright frightening when it does this.

dgiturbo

What I have been doing when I need to make that quick left turn in front of traffic, or clear an intersection is hold some brake pressure with my left foot, bring the RPM's to about 1000 just before its time to go then release the brake and simultaneously stomp on the accelerator as needed. No lag there.
Do agree MB should be made aware. Will mention/demonstrate it at my next dealer visit.