Aux fuel pump V393 pressure question

A Golf CJAA that I am working on has a code for low fuel pressure at the rail:

Address 01: Engine Labels: 03L-906-022-CBE.clb
Control Module Part Number: 03L 997 030 E HW: 03L 907 309 AA
Component and/or Version: R4 2.0l TDI G000AG 9983
Software Coding: 0050078
Work Shop Code: WSC 02455 002 1048576
VCID: 3064C49DA3D3A7C497-8064


1 Fault Found:
000135 - Fuel Rail/System Pressure
P0087 - 006 - Too Low - Intermittent
Freeze Frame:
Fault Status: 00100110
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 258987 km
Time Indication: 0
Date: 2015.14.15
Time: 21:21:40


Freeze Frame:
RPM: 552 /min
Inj. Quantity: 27.5 mg/str
(no units): 15.0
Pressure: 456.0 bar
Pressure: 88.0 bar
Temperature: 70.2°C
Tank Cont.: 10.1 l

In the Self Study pdf document for the CR 2.0 it says that the aux fuel pump supplies the HPFP fuel at 73PSI when things are working correctly. That is not what I found when I tee'd into the line from V393 to the HPFP. I measured a pretty steady 55PSI.
Well that did not look right so I thought that the aux pump is starving the system and the result was low pressure at the rail. So, I ordered a new aux pump and found that the tee'd gauge still read 55PSI.

Am I reading this pressure in the correct place?


From the document:

Auxiliary Fuel Pump V393
The Auxiliary Fuel Pump V393 is a roller-cell pump.
It is located in the engine compartment and has
the task of feeding fuel from the fuel tank to the
high-pressure pump. The Auxiliary Fuel Pump V393
is actuated by the Engine Control Module (ECM)
J623 through a relay and increases the fuel pressure
presupplied by the Transfer Fuel Pump (FP) G6 in the
fuel tank to approximately 73 psi (5 bar).


Effects of Failure
If the Auxiliary Fuel Pump V393 fails, the engine runs
at first with reduced power. An engine startup is not
possible.

Typically those pumps will either work or they won't. And the pump isn't actually what regulates the pressure anyway. If you "dead head" that feed from the pump into your gauge, you'll likely find it is capable of making 150+ psi easily.

Chances are the HPFP is on its way out... BUT, first check a couple things:

Take the little filter screen off the HPFP inlet, the goofy looking little plastic deal on top. Take it to the bench, and blow backwards through it with compressed air on to a clean white shop towel. Look for any little bits of debris. This is a "last chance" filter screen before going into the HPFP. If it gets some stuff in it, it will starve the fuel system.

Next take the fuel metering valve N290 off the top of the HPFP. Look in there for any debris.

Then last stop, take both the fuel pressure sensor G247 (timing belt end) and the rail pressure regulator valve N276 (flywheel end) off the rail and inspect for any debris. It will look like fine silver stuff, almost like anti-sieze paste, but not a whole lot. Does not take much.

If you find anything, the HPFP is bad BUT that only provides the schrapnel.... the actual rail pressure loss is from debris in the injectors.... just one of them not sealing internally causes them to bypass, which means loss of rail pressure.

Thanks
That is what I was looking for.
I did deadhead it yesterday and it did shoot up the pressure to above 150 psi.
I might add that the owner complained that the car goes into limp mode and gets noisy. I witnessed the noisy part which subsided when I unplugged v393...and shortly after the engine died. But the noise was accompanied by a vibration at the metering valve and the plastic screen filter. The car has run fine in my presence even with the noise.
So the next step is to look deeper into the components.
I checked the main fuel filter and found no shrapnel but I think the guy ahead of me very recently changed it.

It is rare to find one of these with a failing HPFP that is still running, as I think the period between "beginning to fail" and "call a tow truck" is quite short. Because like I said, once the metal particles get to a point sufficient to hang just one of the injectors open, then the rail pressure is gone.

Kerma has stated he can successfully clean these injectors. You may be able to save your customer a lot of money by just replacing the HPFP with a reman one, and having Kerma clean the injectors.

OK, so...
My question now is:
Is 55 PSI what the fuel pressure normally is or is there still a problem with that?
What does control that pressure; the fuel metering valve?

I removed and inspected the fuel metering valve, removed the N276, blew out the fuel screen on the fuel temp sensor. I did not find any metallic debris. I did find a couple of specks of something in the metering valve bore in the HPFP. It may have fallen in upon removing the valve. Everything looks spotless.

Did some acceleration runs logs and for the most part the fuel rail pressure seems to be right on the money.
Every once in a while I hear a drone and can feel a vibration in the HPFP metering valve and that will come and go on it's own.

And, I been trying to post this the last few times and forgotten to...
The problems seemed to have started after the VW emission fix was performed.

The car will have extended cranking hard starts periodically as well.

I had a low rail pressure code acompanied with a stall, flashing glowplug light and not even a sputter when trying to restart a couple years back, best I could tell I had a tiny bit of crap in the high pressure side of my hpfp, I took the pump head apart, cleaned it put it back together and here we are 40000 miles later without a hiccup, I never did see anything, but based on the results I figure there must have been something.

The only monitored fuel pressure is the rail pressure, and that is quite high. The HPFP moves more fuel through it and back out the return side (volume wise) than the engine needs to run, just like PD and VE TDIs. So while the rail pressure is maintained at a very high amount, its volume is quite low.

The freeze frame data for the low rail pressure DTC may give a clue. If you say it sometimes has a long crank time when cold, and the freeze frame data confirms that is the same time the DTC event is triggered, you may have a loss of fuel prime somewhere... could be a check valve or something somewhere, or simply a tiny leak. However, unlike the VE, the CR has some pressure everywhere from the tank all the way up, so leaks cannot generally result in air getting in without fuel getting out while the engine is running.

You could also have a rail pressure sensor that is not giving the correct value. While I am sure there is some tool that could be mounted to actually monitor actual rail pressure, it is probably jaw droppingly expensive.

Found this thread by searching for a CR fuel line diagram.
I have a small fuel leak anterior of (what I think is) the tandem pump.
From the fuel filter housing - it’s the second line from the front, runs posterior, loops down and attaches to the posterior side of a cylinder looking thing with square ends.
The line on the anterior side of that item, along with the 2 wires attached to it have fuel and collecting dirt on it.
That line runs to the HPFP attaching to a sensor before making a right angle downward dive into the HPFP.
The other 2 lines running from/to fuel filter-HPFP & HPFP-fuel rail, are both dry and clean.

2 questions:
1. Is this a warrenty item under the fix?
2. Safe to drive to dealership/shop (depending on answer to #1) or have it towed?

This may be a dumb question, but I put a CR aux fuel pump in between my mk2 fuel filter and son 11mm IP. It'd OP is correct in that the aux pump supplies fuel at 73psi. I imagine that that is far too high. Correct?

Way delayed reaction

Just to put a period on the end of my thread, the problem wound up being that for whatever reasons the fuel feeds at the lift pump were disconnected by the dealership at the update visit they were attached in reverse. In to out, out to in. Somehow it managed to run that way…kinda. Once attached properly the car ran fine.

Thread revival...

Ran into it again today.
2012 Jetta CJAA
Blue line is the fuel return from the engine , black is supply to the engine.
It does not fit with the arrow direction on the top of the lift pump.

The fault code:

Address 01: Engine (CJA) Labels: 03L-906-022-CBE.clb
Part No SW: 03L 997 030 M HW: 03L 907 309 AA
Component: R4 2.0l TDI G000AG 9983
Revision: 12H14--- Serial number:
Coding: 0050078
Shop #: WSC 41823 002 1048576
VCID: 3874FCBD4BA37F5333-806C
VINID: 0E69DC70745A25374308318520380F9BD1

1 Fault Found:
000135 - Fuel Rail/System Pressure
P0087 - 002 - Too Low - Intermittent
Freeze Frame:
Fault Status: 00100010
Fault Priority: 2
Fault Frequency: 2
Reset counter: 255
Mileage: 208453 km
Time Indication: 0
Date: 2016.11.06
Time: 13:33:26

Freeze Frame:
RPM: 2070 /min
Inj. Quantity: 17.3 mg/str
(no units): 5.0
Pressure: 1280.0 bar
Pressure: 808.0 bar
Temperature: 86.4°C
Tank Cont.: 21.3 l

I rolled the dice and took a look at the lift pump fuel line connections. They are attached in reverse...supply to the return/return to supply.
The owner had this car just since May and did not have very much in the way of service documentation. He assumes that if the car was registered that it had to have the emission upgrade certification. Some dealership service magic? or did it come from the factory like this? ???

Something to check if you are getting this code.
The car does have hard intermittent starts and once it is back together we'll see if this is the reason why.

Hello. Is your problem fixed. Having same issues.

Problem is fixed

Thanks. I see problem was connections at transfer pump were backwards..? I'm about to take a look at that pump , but I'm sure that will not be my problem. I have vcds and can run the test, but can't seem to find what the specs should be. Thanks for your reply. Have some more work to do.

Seen a decent amount of these with the lines mixed up without anyone touching them. Seems like there was a tech tip or something with regards to this.

There might be an answer to my query here. I Have a 3l v6 tdi on my quattro, 2015. The problem is occasional crank no start. Absolutely nothing, not a puff of vapour. It happened Sunday after a long journey on Saturday, 300km then a fresh fill of diesel. Next morning, nothing, just turning over. Later that day, tried again, and after 10 seconds, it caught and started. It never recurred until last night in a hotel restaurant basement car park miles from home. Nothing worked to shake it to life, locking, unlocking, an extra wait of an hour. Had to call son to collect us. First thing this morning we drove back to the hotel. Met breakdown assistant guy there and we descended the ramps. It started first turn. He scanned, and like I did on Sunday, found no codes. Something is amiss. I'm going to clean the fuel pressure regulator valve on the end of the rail. The vag Self Study Program 840193 indicates only it and the auxiliary pump can cause no start. The valve in particular if it fails to close properly will leak the pressure in the rail needed for the injectors to fire. The HPFP fuel metering valve, and the pressure sensor will at most cause slow running or limp if they fail. Very useful read.