if the sensor is reading 3.5 (vs setpoint of 4.6 bar) wouldn't the control module ramp the pump up (if the pump responded)?

as I said it looks like the pump controls pressure since the parts diagram does not show a regulator or a return line...the only way that could happen is by controlling the volume it pumps, can't vary the speed (it's DC) so the only option is its duty cycle

it looks as if the sensor is good and the pump (or controller) is bad
I guess it could be the sensor, if reading low and the pump tries to compensate by ramping up and over fueling the engine, but you wouldn't get a lean code?

looking at the parts diagram
can't tell if 1 or 2 control units? one item is listed as a qty of 1, the other 2, both are fuel pump control units mntd in the trunk?

they show 2 fuel pumps
an aux pump w/o fuel lines (right) 7
a fuel pump with fuel lines (left) 8
when you look at the lines there is only a line going to the right side
4 in the lower diagram is the controller

 

the left side is the fuel filter module with the syphon jet pump system built in. The right side has both the pumps in it sitting side by side. looks like it has 2 fuel pump control modules, one underneath the rear section of the right door sill plate/seat cushion the other above the rear sam. You can try swapping these 2 modules with each other as they are identical. It is most likely the pumps but this is internet diagnosing at its finest.

You would think that if the sensor was whats wrong it wouldnt throw a lean code but mercedes doesnt like simplicity.


a leaky egr doesnt cause the same problems as an air leak. egr is inert gas so it wont affect afr. - thats off topic anyways as 156 has no egr.

 

There is two control mods, I remember pulling them out.

 

Thanks guys for your help

I will update later

 

I joined EPC

for my VIN there is only 1 main pump and controller
there is only 1 fuel line to the engine rack

there is a diagram for 2 pumps and 2 lines but it says not applicable to my VIN? same for the digram with 2 main pumps?
it does say 2 control units are required?

 

Not sure which year you have.. mine is an 09 and I have 2 pumps.

 

They changed to one pump in 11 or 12 maybe.

 

Hey Guys

Update : I took my car to a specialist MB guy , and he checked the Fuel Pump pressure by connecting a small gauge and then I started the car , the gauge shows around 2.5 bar , even when pressing on the accelerate to 1500-2000 rpm , so he told me it's the fuel pump , and then tested the fuel pressure sensor above the engine , and it shows the vold is 4.85-4.95 , I don't remember , but it was normal , so my guess , I mean his test shows the problem is with the fuel pump , but I don't know which one

those are the numbers that a member of this site ( Ingenieur ) gave me thanks to him

A2044701094
A2044701694

Which one is the fuel pump that mb guy is talking about ?


Thanks again friends and sorry for my questions

 

Not sure I understand your question, but the 1694 part is the main fuel pump on the left side of tank. The 1094 is the auxiliary pump in the right side of tank.

 

Hey guys

As I mentioned in the last reply , checked the Fuel Pump by connecting it to a Fuel Gauge pressure , and it showed some thing between 2.5bar , so the guy told me it's the Fuel Pump

So could you please tell me a trustful site to buy it from online , I am not paying 1000$+ to the dealer for it , prefer to buy it OEM online rather get ripped easily

Thanks for all your help

 

oediscountparts.com

 

I have two fuel pumps here. 60000km on them

 

I want a site that accept paypal please

 

I can accept paypal and get you decent pricing, I'll send you a PM

 

mbonlineparts.com (the one I use), appears to accept PayPal.