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Discussion Starter · #1 ·
I'm having an issue and hope someone can help.

Occasionally (once a week probably) when I am at high revs (4,500 rpm and over), and usually when I gear down and accelerate, my car looses power, big time. It feels like the engine is governed. I can continue driving but can't get power and almost impossible to get to 3,000 rpm. If I turn off the engine and restart, the problem goes away.

Seems like it has to be a fuel system issue caused by the computer (as the problem is resolved by restarting the engine). Any advice?

I drive a 2012 SLK200 (R 172)
 

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Boost leak or a fault with the Mass Air Flow Sensor.

The boost leak (split hose or loose clamp) wouldn't show up on the computer but then it also wouldn't be reset if you restart the car, so I'm thinking MAF fault. Possibly a loose connection on the sensor.

Rather than checking the computer, the technicians need to get under the bonnet and do some basic diagnosis.
 

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Surprisingly, this could - I say 'could' - be a transmission problem. Happens a lot with the larger MBs. Worth asking the question of a techie who knows MBs…

Another one not uncommon in the W202s (and I think early R170s) is the engine puts itself into protect mode and thence into limp mode. I cannot remember the reasons exactly, but something on the lines of the engine sensing a knock situation, then tries to adjust the cam setting and then realising it is all wrong, takes the easy way out and puts you into limp mode. I think the cure was a simple sensor replacement.

There are loads of possibilities, and as said needs someone who can go beyond relying what is spewed out from the OBD socket, but do get someone to look at the knocking one...
 

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Hal, if the car goes into the factory programmed " Limp Home" mode then the MIL (engine warning light) WILL illuminate. The ECU will certainly throw up a fault code on an OBDII reader. I fitted a "tuning box" to my AR Brera 2.4 diesel in 2008 & an overboosting turbo put into "limp home" (50 mph max on the M11). I had t buy an OBDII reader (ELM27) to cancel the MIL...
 

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I did not say 'factory programmed limp-home mode' I said protect and then 'limp'.
Anyway, if you say it is wrong, then who am I to suggest otherwise? My apologies for sharing one of the many known quirks that befalls MB engines over the years. Silly me!
 

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Discussion Starter · #8 ·
Thanks for the comments & suggestion! I'm sure that the car is going into limp mode. That describes its performance exactly. Been talking to a friend who is a good mechanic and we are going to go for a long (300 km) country run this weekend to see if we can get the fault to reoccur.

I'll post the outcome.
 

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Discussion Starter · #9 ·
Got the fault 5 times on our country run and also had the check engine light come on. At my friends garage we got 2 fault codes - P061A22 & P008A21. Checked them on the internet and found that my problem is caused by an error in the engine control unit software. (see below). The issue apparently affects the M271.8 EVO engine in a number of models. Took her into the Benz dealer this morning armed with this information and got the usual rubbish response; fuel pump must be bad, must be driver fault, etc.!! Eventually convinced them to look it up and they realised that MB have issued a ton of updates - including the one below. Car has now had engine and transmission updates installed and I have picked it up from the dealer and I'm going to go for another long drive to make sure that the updates have fixed my problem.


Li47.00-p-054771 is the MB bulletin.

- M271.8 EVO engine has poor accelerator response -

Topic number
LI47.00-P-054771

Date
06-20-2013

Validity
MODEL 172; 204; 207; 212 with M271.8 EVO


Complaint

Engine has poor accelerator response

Engine diagnosis warning lamp lights up

Fault code P008A21 "The pressure in the fuel low-pressure system is too low"


Cause

Due to an error in the engine control unit software, an insufficient fuel pressure in the low-pressure system may be detected in certain driving situations (primarily at high loads and high rpm ranges) although this is not the case.

Remedy

This can be identified by checking the fault freeze frame data. If the value for the low fuel pressure is above 4 bar, the logging of the fault was implausible.

If there is no detectable damage to the fuel system, do not replace any components. Program engine control unit with DVD 05/2013 or later.
 

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Interesting!
But is this exactly the same fault you had before? I ask as this originally sounded more than just 'poor response'.
Please post your test results as I like to keep a list of all the peculiarities of the 271 engine..!
 

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Discussion Starter · #11 ·
Hal,
I wouldn't have referred to my issue as "poor response", (the term limp mode is a much more accurate description) but that's what is associated with the fault code we got. I will post this weekend after my test run.
Evan
 

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Discussion Starter · #12 ·
For those who have an interest, the software upgrade has worked. I've done a number of long drives and haven't had a re-occurrence of the fault. I also had a update for the transmission and there is a significant improvement!
 
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