2008 mercedes c-class 320 cdi 11b800 low fuel pressure

[robbocop33]

Car runs flawlessly,only problem is say at 60mph approx if you really put the foot down the EML comes on and power shuts down slightly.
Code is 11b800,"The control deviation during rail pressure regulation via the quantity control valve is too high".
I've replaced flow control valve on high pressure pump as this was suggested but problem is still there.
Can the fuel pressure regulator sensor on the fuel rail be fine but just fail at a certain request level for more fuel??In my case flooring it at 60?

[robbocop33]

Fuel pressure regulator replaced on fuel rail and problem is still there,for all of you that replied,not! :-)

Edited by robbocop33 on Monday 19th June 21:57

[LordLoveLength]

Did you replace the fuel filter?

[robbocop33]

Yes.

[LordLoveLength]

Is there a low pressure fuel pump near the tank? Does it work and deliver reasonable flow and pressure?

[robbocop33]

I've just tested the in tank fuel pump with the scan tool,but only fir functionality,not sure if my scan tool reads low fuel pressure,it reads fuel rail pressure.The freeze frame my tool took at time of fault shows fuel rail pressure ar 1380 bar,but shows specified fuel pressure at 1530 bar.
Car actually drives perfectly if i drive 'normally',it's only at 60 or thereabouts when you floor it fault occurs,starts perfectly from cold,warm,idles dead steady,accelerates fine when driven leisurely.

[LordLoveLength]

Ideally you want to check the low pressure delivery - could be blocked pump filter / dirt / water or faulty low pressure pump. HP pump will pull fuel through usually but it’s not ideal.

Could be faulty suction control valve on HP pump , or the o ring seal on it, but I’d expect that to be reported as a fuel leak. Worth a look if it’s easily accessed.

[robbocop33]

I've replaced the fuel quantity flow valve on the High pressure pump already.I'll lift the back seat and checkout the intank pump thoroughly,i've heard the mesh filters can sometimes get gunged up on them,thanks for your replies!

[Nick1EST]

Hi, have you fixed this issue? I have exactly same problem and have already replaced PCV on passenger site rail and QCV on HP pump and also fuel filter. Any ideas what else can cause the issue?

[robbocop33]

I ended up selling it,i was 100% it was the High pressure fuel pump which i kept delaying putting on,so i never found out.

[LordLoveLength]

It can be caused by worn injectors - they always leak a little down the return line.
When a little leak becomes a lot you end up with low rail pressure.
Is it worse with a hot engine? A leak off test can identify a failing injector.

[Tony1963]

LordLoveLength said:

It can be caused by worn injectors - they always leak a little down the return line.
When a little leak becomes a lot you end up with low rail pressure.
Is it worse with a hot engine? A leak off test can identify a failing injector.

See post above yours.