Fuel pressure problems

[Uncleben]

Hi, hope everyone had a good christmas.
I've been having fuel cuts when driving, to the point where the car is now undriveable.
I have 2 codes, P310c 'low fuel pressure regulation: fuel pressure breaks down sporadically' and P1063 'fuel pressure regulation value below lower control limit'
It seems these are related to the low pressure side of the system, so far I have changed the lift pump, the pump control module, the low pressure valve on the hpfp and the fuel filter, none of which have fixed the issue.
I now suspect the hpfp (well, the valve on the top N276?) even though I don't have any of the codes that would be associated with that, such as P0087 and P2293, but don't see what else it could be, cam follower was replaced about 25k ago.
Has anyone had similar problems, and does anyone have a good hpfp for sale?
Car is 2005 AWX engine, located Worcestershire

[pudding]

Might be worth checking the HPFP follower again as 25K is a fair old stint for one of those, especially if the car is remapped and/or has upgraded internals.

Have a good sniff around in the engine bay of obvious leaks, and how does the engine start from cold? Quickly and smoothly?

[Uncleben]

Car starts and idles fine, when you rev it or apply throttle to drive it just dies, but will fire back up no problem.
Think I will remove the hpfp to check the follower just to rule it out 

[Uncleben]

Forgot to add, the car is completely standard.

[pudding]

OK, maybe it's time to get the big guns out - VCDS, if you have it?  You need to measure the fuel pressures with the engine running and also under load to see which pump is getting a bit long in the tooth.

The in-tank pump should deliver between 3.5 - 6 bar when driving and the high pressure pump should be at 50 bar at idle, and rising up to 109.9 bar under full load.

Are you Uncle Ben as in the chap who makes the microwave rice packets? 

[Uncleben]

Yes, that's me!
I don't have access to vagcom, but do have access to an audatex diagnostic system which I used today to measure some values, I didn't really know what I was doing so will just post the values I recorded and hopefully you can make sense of them!
Measuring block 103, fuel pressure(low) 4-5bar at idle, didn't measure this when revved to see if it drops, doh!
Measuring block 106, (duty cycle?) 45% at idle, rising to 90% when revved.
 Measuring block 140, fuel rail pressure, was 50bar idle rising to 90bar when revved to 2500rpm, then dropped to about 2 as it died
The specified and actual rail pressures are within 2 bar all the way from 50 to 90 when it dies.
The only code that comes back each time it dies is P310c low fuel pressure regulation ;fuel pressure breaks down sporadically, from what I've read, that does not relate to hpfp?
Cheers for your help

[pudding]

106 is fuel rail pressure and the % duty is the engine ECU's PWM command on the fuel pump controller, which is under the rear seat.  90% is massive, it shouldn't be anywhere near that high at only 2500rpm!

When was the fuel filter last changed?  I suspect that is either completely clogged if it's never been changed, or the in-tank pump is dying, hence why the high pressure pump can't cope either.

[Uncleben]

Fuel filter has been done (6.6bar), along with a known working lift pump from a mates car (to rule out a faulty secondhand pump I'd fitted being faulty)

According to Ross-tech, P310c likely causes are faulty lift pump (g6) clogged filter or empty fuel reservoir.

I have recently ran the fuel tank to 0 miles to empty, but this issue was already present by then.

[pudding]

Blue and black fuel lines put back in their correct orientation on the filter?  Some folk have made that mistake. Although saying that, I can't remember if the engine doesn't run at all, or if just enough fuel gets through for idle and not much else.

Fuel pump controller under the seat getting very hot?

It might be time to book it in for visual inspection because a car with 2 fuel pumps, a pump controller and 3 fuel pressure sensors isn't the easiest thing to diagnose on a forum.

[Uncleben]

The fuel filter was the last thing i replaced so can rule the pipes out.
Haven't checked the controller getting hot, but did replace it for a known working one which made no difference.
I appreciate its not easy without seeing the car, I just cant find any mobile mechanics willing to delve into complex diagnostics!
I will measure fuel pressure at the lpfp again, but see if it drops when revved like it does at the hpfp, if so then that must be a fault with the low pressure side, as a faulty hpfp wouldn't affect the low pressure?
Really appreciate your help 

Edit: so i've just measured fuel pressure at the LPFP, was 4.8 bar at idle, rising to 6 when driven, dropping to below 2 as the engine died.
 So a drop in the low pressure side would cause a drop in the high pressure side but not vice versa? i.e; a faulty hpfp wouldnt cause the pressure to drop at the lpfp, but a faulty lpfp would cause the pressure to drop at the hpfp?
so it seems the problem is still with the low pressure side, as the P310C code is telling me!

[pudding]

It's a tricky one because a bad HPFP, or relief valve, bleeding off fuel pressure abruptly could cause a misdiagnosed LPFP!  Similarly, a bad LPFP can also cause fuel pressure faults, so the two are heavily interlinked.

That's the trouble with modern engines and fault codes. A component flagged as faulty could be the result of something else failing.  Bad grounds or a bad CAN gateway for example can light up a dash like a Christmas tree, and people start throwing new modules at the car, which doesn't fix the root cause 

Given the LPFP and HPFP are similarly priced (new oem), an element of parts cannon firing could be required.  The used LPFP you fitted, was it the exact same part number of your original one?  They have been updated by VW a couple of times over the years.  The early ones were prone to overheating and causing fuel cuts.  VW's fix was to simply remove the lid from the pump housing 

Given the symptoms, I suspect it's the  low pressure side.  It sounds like it's running out of puff as the load increases because it's old and tired perhaps.  The crazy 90% duty kind of hints at that.

And as last minute thought, have you checked the HPFP cam follower hasn't worn through and the pump's piston isn't riding on the cam?  That severely limits fuel volume!

[Uncleben]

Think I may have to admit defeat, the car needs a lot spending on it as is (cambelt due, noisy chain, noisy flywheel, rusty sills and front wing) mot has expired too, car has done 193k and its showing now!
I've had nearly 6 yrs problem free from it, so now I think everything is going wrong at once! don't think it is worth spending more money, especially as I've already spent on replacing all the low pressure components, and as that is where the problem still seems to be then do I just replace it all again but with genuine new parts?
may just sell as is and cut my losses!
The lpfp I bought off eBay was the exact same, then I tried one out of a 2010 octavia which was the same part number apart from the last letter, still to no avail.
I will inspect the cam follower just to rule it out as it has only been about 25k since I had it changed last, but you never know!
I appreciate all your help regarding this issue, but, as you say, trying to diagnose problems without seeing the car is a pain.
Cheers.

[pudding]

I can totally understand that. Maybe it's time to upgrade to a newer model, but it sounds like yours has done extremely well given the mileage!

[Uncleben]

You were supposed to talk me in to keeping and fixing it!
While I'm pondering my options I decided to take the original lift pump apart out of curiosity, all I noticed was a lot of dirt/sediment in the bottom of the bowl, is that normal? there is a superfine mesh filter on the bottom so not sure how it got through, but even so, the fuel filter would have prevented anything reaching the engine.

[pudding]

But that would make me a hypocrite as I gave up on mine in November    It ran fine though, so not really the same situation, it was just time to move on to something more relaxing in traffic.

There shouldn't be a lot of dirt inside the bowl but the pre-filter is generally always filthy.  You could try a mechanical fuel pressure gauge to verify the sensors aren't lying?

I think you can plumb it into the Schrader valve on the HPFP.