There has been a behaviour that has been plaguing some member cars for many months. Some of you complained about the throttle flaps closing for a split second and then re-opening on you during part throttle acceleration.

This behaviour doesn't occur if you start off and go directly to WOT, but if you are cruising around at part throttle and try to accelerate you will likely run into this if you have this problem in your car.

This is not a mechanical problem. It is attributed to the dreaded "Secondary Airpump Recall Flash" that many people went through last year. During this campaign MB added some code which implemented load limiting. (I know this has been posted many times in the past, but I am reiterating because I have some new information.). I am not sure if some of the code falls over onto the EGS module or if it is isolated to the ECU only.

There is some data to suggest that some cars still haven't been able to get rid of this load limit problem.

How do you know if you have this problem? Very easy to find out:

1) Go onto a stretch of road and maintain a constant speed (say 50mph)
2) Slowly depress the accelerator and work your way to WOT.
3) At some point during this process you should feel a sudden jerk. The sensation will be like the throttle body flap suddenly closed shut on you for a split second but the car will then keep going on its way.

Now, take the car to someone with a STAR DAS device and do a "Quick Test" on all the function groups. If you have this problem, Code P2040D ("Load Limit Active") should be stored in your ME2.8.

The thing to remember here is if you do a dyno pull, or 1/4mile run, or anything where you are going WOT right away you will not notice this. This behaviour seems to be isolated to part throttle only.

Now for some data:

- My personal ECU with the original VRP tune that was developed on RFlow's car through Active Autowerke has this problem (Code is constantly presenting itself). My car is a 2003.

- E55 Baller has K2 programming and I am sure if he checks he will see he has this problem. We all know Isaac's car is strong because it ran an 11.11 @ 125mph. Isaac's car is a 2004.

- Marcus with his VR550 has this code stored (we just found out today) and his VRP tune is the newer one developed with Powerchip. His car runs strong and dyno'd well. Marcus has a 2005.

3 different tunes, 3 different years, all the same behaviour, so its not related to 1 particular tuner or year of vehicle.

I am sure there are more of you out there but you just don't know it. It's very interesting that these load limits are still present at part throttle driving even though they were effectively removed from the ECU code during the tuning process.

Nate's blistering E55 does not have this problem but I had a new EGS put on his car with all the load limits removed.

I purposely left my own ECU alone because I have been systematically going through everything on the car (mechanical and software related) to try and figure out the source. I have eliminated everything except for the EGS. I am waiting on my EGS to arrive from Germany with all the load limits removed on it like we did for Nate. Once I put this back in my car I will verify if the P2040D goes away.

Either the EGS alone will resolve this, or the EGS and ECU both have to be matched up and revised to completely eliminate the problem. I will post more data as I find it.

If any of you have this behaviour please post up.. I'd like to get a greater sampling of data to see what software you are running and what year your car is.

 

my car has Evosport 175mm pulley and stock ecu and this happens ....

 

Hey vrus, I'lll give this a try when I bring my car out of storage...should be soon since I have to go for emissions testing. But first, I'll have to wait for all this snow to melt away.

 

As Victor mentioned my car does this. It is a VERY tricky problem and VERY difficult to duplicate. With my car there is only a limited window in which I can induce this to happen, and even when conditions are optimal I may not be able to do it more than once. Now that it is very cold here in Chicago I've taken the car out only a few times. Today I took it over to CPT to pull the codes to see what the ECU was saying about this "bucking". I never get on the throttle hard with the car until it warms up, but as Victor said, this won't happen under heavy throttle. I was merging on the highway today - car was just a little shy of being fully warmed up - and as I increased throttle just a little bit to match highways speed, boom at 60mph/2000rpm - throttle plate closed for a second, and then reopens. I tried a good 4-5 more times and it would not do it again. So then after cruising for a bit I rolled into it from 60 just to maybe 30-40% throttle and at 80mph, again, throttle closed. I then did a full throttle run from 70-130... smooth as can be. It did not do it again the rest of the day.

In warm weather my car does not do this. After getting up to full temperature my car does not do this. On the dyno my car does not do this. At full throttle my car does not do this. It has to be very cold, on the highway with good airflow, when the car is not heat soaked, and when you are gently rolling into the throttle. It's still not 100% consistent, it's very temperamental, and if you try too many times you'll wind up getting the car fully up to temp and it won't do it at all anymore.

Hopefully with some work we'll get this problem resolved. On the positive side it doesn't affect peak power output, but it just makes for kind of an annoying driving experience when the car is not fully up to temp and could theoretically present a hazard if you are counting on the car to get moving and it cuts throttle - but ESP can do the same thing to you...

-m

 

Is this happening to cars with mods or all cars?

 

My car does the samething
I got tried explaining it to my SA. He said it was normal for the 55's acting that way.

 

I will try this on my E55 next time I am out with it.

However, I have had this problem on my C32 following service which included the CPU reflash. It would occur quite predictably in low winter temps and at almost in the same location. Car had sat all day in outdoor commuter lot, outside temperature below freezing, approximately 5 minutes after start, accelerating moderately uphill on merge ramp from 40-60, throttle momentarily closes with violent jerk as thrust is lost and restored. This continues even after CPU is sent to Powerchip for reflash.

 

It is harder to reach the load limiter on a stock car, but it can and does happen even when a car is stock. The more power you put through the car, the easier and more likely it is to hit the load limiter.

-m

 

That is a good description of the problem, I am surprised this may also happen on C32s!

-m

 

Can you provide more information about the intended funtion of the 'load limiter'?

Also, I probably understated when I said moderate acceleration in my description. As I think about it further, I was accelerating somewhere between moderately and aggressively on a moderately steep incline just below the throttle position that would induce an automatic kickdown (intentional since my car hadn't comletely warmed up.) Those conditions certainly contributed to the jerk being so violent.

 

As far as I am aware (and those who may know/understand more, please correct/amend my statement) the load limiter's sole purpose is to protect the engine/drivetrain against "loads" that may put excessive strain on them and cause premature failure. It is my thought that this is done as a direct curb against tuners and tuner cars, as to prevent blown up tuner cars from showing up at the dealership looking for warranty repairs, thus making these limiters extremely hard to find and equally hard to remove completely.

In my experience the throttle position can be anywhere from ~25% to ~75% and still induce these limiters, so it sounds like what you are experiencing with your C32 is very similar.

-m

 

Interesting, This sounds almost like a compressor surge issue causing an overboost condition.

With Forced induced cars you can get the turbos and superchargers to overboost at part throttle right around peak torque with a partial throttle. This overboost hit's the limit in the ecu and the car dumps boost by either closing the throttle plate, opening the throttle plate full/retarding the timing and pulling fuel all of this is to reduce BMEP.

 

......Is stock and it did not do it until the dealer reflashed it with updates

 

turbochargers - absolutely
superchargers - not at all

supercharger is mechanical and belt driven from the crank so this will not happen. reason why this entire thing is happing in the cold is that cold air combusts better and makes more power that leads to hitting the load limiters.

my car does exactly what's being described by other in this thread - i'd love to get rid of this

 

+1


my car does exactly what's being described by other in this thread - i'd love to get rid of this[/QUOTE]

 

Actually it will happen on a supercharged car.

Cold air doesn't combust better it's DENSER, surge is a mass air issue NOT a pressure issue (Which is what you are assuming) Since the cold air is denser and the intercooler is more efficient at retaining that density you are hitting the mass load limits. Part throttle is easier to do it on since you have a higher intake velocity with reduced cylinder filling causing a surge condition due to the excess flow of the supercharger. Remember there is no wastegate to limit the flow rate to the compressor since it's flow rate is fixed to RPM.

 

Victor,

We need to find a virgin ECU. One question, could this also be related to the quick acceleration to 3/4 throttle, lift, and huge kick or buck issue? Here is a link that describes what I am talking about.

https://mbworld.org/forums/w211-amg/...g-off-wot.html

 

That's caused by the pressure spike from the drop throttle and it having nowhere to go. It also has a rich spike associated with it since the ecu will measure the pressure spike

 

With our throttle upstream from the supercharger, how does its closing create a “pressure spike?”

 

It's much like a jakebrake on a tractor trailer. The vac acts as an airspring creating a spike

 

Thanks for the explanation. So how does this manifest itself in full load situations? If the intent is to limit load and I'm only noticing it at partial throttle, is it happening at WOT but just harder to notice?

 

..... BUT our cars do not have a MAF sensor and run from a MAP sensor which will not be affected by the density of the air or the temperature of the air. and there IS a bypass valve that lets the boost out from the supercharger. please check your facts before misinforming people.

 

Have exactly the same problem and have been trying for months to fix it as I thought it was due to the computer not being initialized correctly... Testing Testing every freaking thing...

This problem gave the dyno operator grief as well and we spent hours on das trying to solve it...

Solution yet?

 

Actually you might want to check your facts.

ME 2.8 uses only two things to figure out the charge mass. A MAP sensor and a Temp Sensor to provide density offset for the MAP.

The Bypass valve let's the intake bypass the supercharger when running under a vacuum it does not "Let the boost out from the supercharger"

ME 2.8 is Load based engine mapping, IE it reads boost, Intake temp and the DBW throttle request. it figures out the fueling and timing by reading a 3d lookup table based on those inputs. anything off the tables will cause the ecu to loose its mind. It will also use the O2 sensors to trim the mixture both short term and long term and Knock sensors to trim the timing.

Now these tables are written using a mathematical model of the motor and ANYTHING that deviates from that mathmotor will start to cause issues

 

i stand corrected on the air density part.

but here is a a perfect example for you of an E55 dumping boost with stock and aftermarket pullies. obviously boost should not drop off with the rpm rising as it would spin the blower faster and make more boost. but as you can see here in this boost log there is clearly a valve that dumps the boost....