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My M is still dead

1K views 8 replies 9 participants last post by  Wolfgang 
#1 ·
Ok, Ive changed the fuel pump, the fuel pressure is perfect, i have new/updated fuel filters, new ignition wires and spark plugs, a new cps and it has already had the cats replaced. With all this work, the truck will start up nice and strong, run for about 10-12 seconds then stall out. Is there anything else that could be wrong?? please help, ive been reading alot of posts and these things are most of the problems that seem to be popping up, and if anyone has any links to other bw about this or other forum posts, please post them. Thanks guys.
 
#2 ·
I don't know how the fuel venting works in these vehicles but if the vent was partially blocked it would cause this exact behaviour. Air leaks in too slow and so as the fuel is pumped it produces a vacuum which the pump cannot overcome and so the engine stops due to fuel starvation. When you crank it again enough air has leaked in to start it but then the cycle repeats.

I would try starting it with the fuel cap removed.
 
#3 ·
Obviously there is no check eng. light on. It could be a number of things, like a bad key. If you have a spare key try that one and if the same problem occurs, it is probably your DAS system, which means the key could be good, but the DAS module is not recognizing it. Does the truck keep stalling every time you restart it? Also look at you odometer the next time it stalls and see if the words START ERROR appear.
 
#5 · (Edited)
You are really wasting your money on blind repairs.

Find a real OBDII specialist who really understands the readings from the OBDII, the CAN bus, and the various vehicle controllers. They normally use good trouble shooting OBDII/CAN computers/interfaces, analyzers, and other testing equipment. Mercedes is no different than any other electronic based vehicle.

Any experienced/educated mechanic that understands vehicle electronics, will use a multi-channel 4/2 channel oscilloscope together with other specialized hardware, to gather readings (pressure, ignition readings, timing, firing patterns, VE, sensor signal shapes, etc) which can be used to pinpoint if it is a sensor (MAF, CPS, etc) coils, controller, etc. They use multiple readings from key parts of the engine electronics, exhaust, fuel pressure readings, signals from the Maf, etc. to understand the exact state of the engine and where the problem is coming from. Each electronic/electrical problem has a specific signal/amplitude signature and together with the other measurements: fuel pressure, exhaust readings, etc. is enough data for an experienced mechanic to find where is the problem or to discard the elements that are working fine: MAF, CPS, etc.

Mercedes Benz mechanics seem just trained to blindly change parts and not to understand the vehicle electronics and identify the failing part. It seems that very few of them are trained enough to debug problematic vehicle electronics and most of them seem to choose the more expensive (profitable for the dealer) and less time consumming workflow. They will change a transmission, when only the transmission controller or a solenoid is bad, or will change O2 sensors, catalytic converters, when only the MAF sensor is dirty or failing.

The link below has a nice article discussing various OBDII/CAN scanners:

http://www.x431usa.com/Roundel%20Cracking-The-Code-May2006.pdf



Though, my blondie wife says you need to get another "M" whatever that may mean.. :D :crybaby2:

AC
 
#8 ·
hi bowen ive the same problem and changed numerous things, the car starts fine then dies when giving it a bit of throttle, but when eventuly gets to temp the car seems ok?
let me know how you get on best off luck,
there must be someone out there, who can say, YES, its that.
regards
 
#9 · (Edited)
This looks like a fuel trim malfunction to me. It could be caused by many different things, like for example air leaks, malfunctioning intake air temperature, malfunctioning mass air flow sensor (even without throwing a MAF diagnostic code) etc. etc. Several DTBs pertain to this topic and describe in detail how to troubleshoot it, with rather long diagnostic trees. Access is available by subscribing at http://www.startekinfo.com.

Under warranty a Mercedes-Benz Tech is only supposed to replace a verfied failed part. Exhanged parts are sent back to Mercedes and tested. If they test fine, that means did not fail, then the dealer is charged back for this amount.

As a start some great training and overview files are online at this location:
http://www.mercedestechstore.com/pdfs/index.htm

A book is available, by Charles Probst, Bosch Fuel Injection and Engine Management including many troubleshooting tips.
Amazon.com: Bosch Fuel Injection and Engine Management (Bosch): Books: Charles O. Probst

Looking back, electronic fuel injection started with the Bosch D-Jetronic and celebrates its 40th birthday this summer. It first appeared in the 1969 250CE, and just a little earlier in the 1.6 liter VW.
 
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