Mbest11

Hey guys,
I need a little help with my w212 merc.

its a 2010 250 cdi 150 kw.
Problem: if i accelerate hard, my engine goes to limp mode and engine light comes on.
i checked the car with Deplhi and it is showing a "fuel pump electrical foult" output too low. this foult appears every time i start engine.
if i drive car quietly then it drives normally. But if i step on the throttle hard then the car goes to limp mode and appears another fault - "fuel pressure fault". -if i delete it then car runs normally again.

-i have changed the fuel pump inside my fueltank- no result
- and i have changed the high pressure pump in engine. - no result.

as i understand the problem is that the engine does not get enough fuel from the tank, and when i accelerate then it is lacking of it and then comes limp mode.
what could be the couse of it?

any help would be appreciated

Mbest11

today changed the fuel pump control module - no result.
i cleaned every connector and even grinded ground connectors. for better connection.- no result.

But today noticed something interesting... when i started the car then the interior light was on and if i gently rise rpm on engine, then the light pulb on ceiling got brighter. And if i gave a good hard throttle, then the ceiling light was lacking of voltage and did not shine as bright. Like it was lacking of voltage. it could be something with the alternator. And also i noticed that my engine belt was flapping too much. maybe the slipping belt could couse voltage loss on hard acceleration so that the fulepump also cant get enough voltage and cant supply the engine with enough fuel.?!? (just thinking loud)

So tomorrow i will replace the engine belt and belt tensioner.

Maybe someone had something like this before?
any info would be great!

kbob999

First - I don't have the 250 CDI engine, but the 3.0 V6 Diesel.
Second - have you replaced the fuel filter? This is the first item to swap when you have fuel issues with the diesel. Diesel fuel can be dirty compared to gasoline.
Last - the throttle pedal is 'by wire' and they are known to fail. This could also be a potential for the problem.

Check your battery voltage by using a plug in voltage meter in your cig lighter while running and not running. I do this all the time to keep track of alternator issues.

Let us know how it turns out.

Mbest11

today i installed new belt tensioner and new belt. - no result!








i have trouble codes:


P062a - "Fuel pump output- electrical foult or open circuit" (that comes after i start the car)





P0087 - "fuel pressure below limit value" (that comes after hard throttle.)


so i really think that it is something to do with the electric system.





Thanks for your toughts!


I will mesure the voltage from socket and see is the alternator charging enough.


first thing on monday will change the fuel filter.


I believe that throttle is not related to this. becouse throttle is responding good, if i push it. no glitches there.





Thanks for thinking with me

Mbest11

changed the fuel filter- no result.

Measured the voltage from 12v socket and the reading was interesting- it was 11,8 to 12,5 and if i slightly rise the rpm then the voltage also rise to 14v as it should be.
but when i push throttle hard then it was only 12v as if the alternator did not gave enough voltage.

So im guessing the next step is alternator change.

my question is why does the cars ECU dont recognise that the alternators output is not enough- there is no foult codes.
And can the bad alternator couse low fuel pressure because of the electric fuel pump?

Arrie

I think 12 volts should be enough to run the fuel pump correctly. Also, when you give hard throttle the car may have been programmed to take alternator charging off like it probably also takes the A/C compressor off to allow full engine power to move the car. Hard acceleration is only a momentary occurrence so the alternator can be on idle for a short time.

Sunnyslope48

Your codes are telling you that you have a problem with the fuel pump or the circuit that powers the fuel pump,so the fuel pump output is sub-par, and that if you run the engine hard, your fuel pressure is dropping too much. Repair the fuel pump/circuit and the P0087 will likely go away without any additional work or diagnosis. When you say you measured the voltage at the 'socket', exactly what does this mean? I take that to mean the cigarette lighter/aux socket in the interior of the car. You need to check voltage at the last connector into the fuel pump, or on the b+ wire into the pump.

https://www.alldata.com/blog-entry-o...mil-dtc-p62a00

Mbest11

Update...
so i took off the alternator and the alternator pulley clutch was bad (stuck) -installed new alternator.
Cant see any flicking interior lights and briefly car ran good... everything was ok.
But after 5 min driving and testing... Limp mode and "insert coin"(engine light) came on...
So pulled the codes and there was p0089 code- that indicated to faulty pressure regulator valve. - changed that too.

after clearing all the codes- car drove fine for 10 minutes... and then again it was lacking of power. but no engine light.
and diagnostic tool did not show any faults. and after 10 min playing and testing with engine the "low rail pressure fault" came.

To clarify. my engine is like sputtering when i throttle hard. its like not rising rpm over 2,500.
and if i push throttle gently and slowly then rpm rises okay.
also having trouble starting the engine. sometime it takes 2 times to start engine (20 sec. cranking) sometimes starts up just fine.

Frustrating...
So i have new alternator and new rail pressure valve.- no result.

Next, I will check the voltage to the pump....

Very thankful for you guys thinking with me.

kajtek1

You have car model that never made it to America, but I assume it is close sibling to E250 Bluetec we have.
Fuel system has electric pump inside the tank, that primes HP pump mounted on the engine.
The first code you post indicate some kind if electrical defect at the tank unit.
The other codes could be secondary effect.
In each such case - replacing fuel filter should be the 1st thing to do and posting that in diesel section might get better exposure.

Mbest11

update..
in last post i forgot to add that i changed the fuel filter too- no result.

Kajtek1- yes, thats my thoughts too. that it is all related and it has to be the fuel that is feeded to engine.

today i installed a "T" pipe in front of fuel filter and installed manometer to measure fuel pressure.
In idle it was just 1,8 Bar =26psi.
and when i pushed the throttle the pressure did not rise, it was always only 1,8 Bar =26psi.
When searching in forums, i found that it must be atleast 4,1bar= 59psi or it would be starving on fuel.
So my next step is to diagnose the low output on feed unit.
tomorrow will check the voltage to pump and try to replace fuel pump (maybe in first time i got deffective unit- it was used unit).

Mbest11

Update.
Today i tested the fuel pump directly. I istalled a manometer directly to fuel pump outlet, then it was good results on pressure. pressure was over 5bar.( 4,1bar was needed.)
So i tested with "T" hose, then the pressure was 1,8bar. and when the fuel pump stopped then pressure instantly dropped- is that normal, or should the pressure stay at hoses and system?
But the pressure intantly dropped when fuel pump stopped. as the all pressure whent back to fuel tank by return line.
Does anybody know, shouldnt the pressure that is pumped to fuel system hold? and the sound in fuel tank is also as the fuel is circulating while pump is active. that means that all the fuel that is returning to fuel tank, and there cant be any 4 bars of pressure in lines.

what is the release valve on these engines, that is allowing fuel back to tank?
Or is it normal?
any thoughts?

kajtek1

Sometimes fuel lines have a check valve to hold some pressure, but starting any pump under full pressure is asking for motor to burn out, so some designs let it drop to 0.
I would not worry why the pressure drops when you shut off the system, but why the 5 bars at the pump makes only 1.8 bar at the filter. You have to have a regulator on the line and looks like it is malfunctioning.

Mbest11

SOLVED
Yes the problem was that the pressure was released too early back to the tank. that means there was almost no pressure just a free flow back to tank all the time.
And i changed the one last thing that regulates the low pressure in system and that was located on the high pressure pump, its called "quantity control valve"

i dont know maybe the valve was bad or was it not communicating with my ecu. either way i changed that and car runs like new.

Kajtek1- thanks for your thoughts.

I hope someone finds this whole discussion useful.

my nightmare is finally over.... until next "insert coin" light comes up

drcool71

Hi
excellent guidance I’m having similar problems
Is their any guide to locate cannot seem to
locate this valve or where abouts of high pressure
fuel pump

Model is
E250cdi 2010 w212
please
thanks

konigstiger

Haci

same problem ( full diesel + Protec ) (clean system) after dead VALVE (Y94 SENSOR) 🤣 tomorrow i clean valve or change . Many thanks INFO.