Need help on CDI Fuel rail Pressure error

[mdelfunt]

Hey guys, been a while since I was here. Got a new problem on my 06 E320 CDI. It now has 313k miles. It's going into Limp mode and getting a P2047-1 "Rail pressure monitoring via volume control valve The rail pressure is too low". The car started this all of a sudden and left me in Limp mode on the side of the road. It will crank and runs good until you accelerate typically over 3k RPM's. Then it will kill the engine. At times, it will run but limit it to 3K RPM's. It has a NEW OEM fuel tank pump and OEM filter.
On my scanner, I've been watching fuel pressure along with the Quantity Control valve (Y74), and Pressure Regulator valve (Y94). Pressure starts out at around 480 bars at idle and moves up as I accelerate. I've seen it get as high as maybe 650 bar. When I get near 3k RPM's I can see the pressure start to trend downward until the engine dies. The Quantity Control valve and Pressure regulator valve appear to be doing something but I can tell what the root cause is since they all seem to fall off at the same time when the engine dies. I've read that the Quantity Control valve (Y74) and Pressure Regulator valve (Y94) are likely culprits but I don't want to start changing parts too early. I don't have a STAR to manipulate these two valves. I suppose it's also possible for the HPFP is bad or even leaky injectors. BTW, dealer wanted to change HPFP, Fuel Rail/Regulator, and Injectors to fix it.

How can I narrow this down to take the next steps?
I get conflicting information about whether the Pressure Regulator can be purchased separate from the Fuel rail. Is that true?

 

[mersum1es]

You can measure injector tank line leak without any diagnostics.

You can buy 2nd hand regulator or perhaps directly by Bosch part number. Dealer sells whole assembly - joy of the aftersales high profit.

Which one is more expensive, get a star session (indy), or start swapping parts? If I would need to change blindly something, I would start fuel quantity valve (after injector leak is rules out).

 

[mdelfunt]

You are correct... I can do the leak down test without STAR.
As part of an insurance claim, I had the car at the Dealer for a 6 days (diagnosing it) and they said they would need to change the HPFP, Fuel rail, and injectors. They thought it was the tank fuel pump and replaced that. But it did the same thing. The insurance company would not put any more money into the car so I took it home. I typically do my own work on it. I'm wondering if taking the connector off the Quantity Control valve and testing it will show me anything? I can trend all the values on my scanner but I can't manipulate the output.

 

[mersum1es]

If I recall right, SDS test for FQV is measuring pressure overshoots when pressure is changed. But you would need set value AND measured value to monitor that.

 

[mdelfunt]

Solved.
For anyone in the future, the problem was the Quantity Control Valve that was preventing the rail pressure from achieving desired. It took 30 minutes to change and cost less than $100.

 

[mersum1es]

Glad you got sorted by first guess , yeah like said fuel quantity valve is very common to fail.