Hiya guys, I'm really hoping someone can help with this issue. 

Started off as a p0087 low rail pressure and limp mode under load. 

Then developed a slight rough idle in park and neutral, and erratic in drive and reverse. 

Changed fuel filter and FPR valve, no difference. 

Then developed into really erratic idle in drive gears and kept trying to stall when coming to a complete stop. Until finally it did stall. Wouldn't restart. 

After checking fuel rail pressure whilst cranking (200psi after 10 secs) I figured it was the hpfp. 

Have changed that, got the car started, ran around for a day. Then stalled coming up to a junction, with no restart. 

Now thinking lpfp, replaced that now have it started again, but still have the idle issue, and a bit too scared to drive it to see if it dies when coming to a stop.

Note: have also replaced the fuel pump controller that sits on the fuel tank. 

Did a leak off test and getting around 30-60 ml per injector after 3-4 minutes which seems low to me? 

Any ideas 

Just now, Svensamios said:

Hiya guys, I'm really hoping someone can help with this issue. 

Started off as a p0087 low rail pressure and limp mode under load. 

Then developed a slight rough idle in park and neutral, and erratic in drive and reverse. 

Changed fuel filter and FPR valve, no difference. 

Then developed into really erratic idle in drive gears and kept trying to stall when coming to a complete stop. Until finally it did stall. Wouldn't restart. 

After checking fuel rail pressure whilst cranking (200psi after 10 secs) I figured it was the hpfp. 

Have changed that, got the car started, ran around for a day. Then stalled coming up to a junction, with no restart. 

Now thinking lpfp, replaced that now have it started again, but still have the idle issue, and a bit too scared to drive it to see if it dies when coming to a stop.

Note: have also replaced the fuel pump controller that sits on the fuel tank. 

Did a leak off test and getting around 30-60 ml per injector after 3-4 minutes which seems low to me? 

Any ideas 

Meant to say it's an A6 C7 3.0tdi CDUC Quattro Avant 2012

Sorry to hear of your issue, but well done for the diagnostic work done so far. Could this be an injector seal leaking I wonder? Or bad injector in general? 

Do you mean the copper seals? If so they were all replaced when it was stripped down for the hpfp So wouldn't have thought it would be them, but I was thinking that it could be the injectors but all 6 seem to give a low amount of return, and from what little I know, if the injectors are bad they tend to flood out? I have the results written down, I'll find them and post them here. 

4 minutes ago, Svensamios said:

Do you mean the copper seals? If so they were all replaced when it was stripped down for the hpfp So wouldn't have thought it would be them, but I was thinking that it could be the injectors but all 6 seem to give a low amount of return, and from what little I know, if the injectors are bad they tend to flood out? I have the results written down, I'll find them and post them here. 

Yep I mean the copper seals but if you've changed them then that's good. I know what you mean, it'd be very unlikely all 6 to go at the same time. 

3 minutes ago, Svensamios said:

Do you mean the copper seals? If so they were all replaced when it was stripped down for the hpfp So wouldn't have thought it would be them, but I was thinking that it could be the injectors but all 6 seem to give a low amount of return, and from what little I know, if the injectors are bad they tend to flood out? I have the results written down, I'll find them and post them here. 

Leak of test results. 3min test on idle. 

Cyl 1 - 40ml

Cyl 2 - 60ml

Cyl 3 - 30ml

Cyl 4 - 50ml

Cyl 5 - 40ml

Cyl 6 - 40ml

1 minute ago, Steve Q said:

Yep I mean the copper seals but if you've changed them then that's good. I know what you mean, it'd be very unlikely all 6 to go at the same time. 

That's what I thought. But I'm getting to the point where it's got an entirely new fuel system. I can't see it being the pressure sensor as the reading I get on live data, seem to be correct, and I can't see it being the relay, from my understanding they either work or they don't, but could be wrong. 

If you have almost eliminated a fuel fault, perhaps it is time to consider an electric or electronic problem. Have you had it on a decent diagnostic scanner?

55 minutes ago, cliffcoggin said:

If you have almost eliminated a fuel fault, perhaps it is time to consider an electric or electronic problem. Have you had it on a decent diagnostic scanner?

I've got a snap off solus unit and I've got a knock off Delphi unit, haven't tried the Delphi. 

As far as codes go, I've got: 

4698-U1113 - function restriction due to received malfunction value - open or shot to plus 

4699-U1113 - function restriction due to received malfunction value - open circuit

7150-P1698 - please check DTC memory of steering wheel electronics 

But I have a feeling they're related to a clock spring issue. Clock spring went a few months ago, replaced with a complete second hand unit, and the light I had for the airbag went out but got an ESP light and the steering angle sensor won't calibrate. 

1 hour ago, cliffcoggin said:

If you have almost eliminated a fuel fault, perhaps it is time to consider an electric or electronic problem. Have you had it on a decent diagnostic scanner?

I also got a video of the injection variation, but I'll be honest I don't really know what it means. Have attached a couple of screenshots as it won't let upload the video

Had a search through the forum, a fellow member had a similar issue and it was the injectors: 

https://www.audiownersclub.com/forums/topic/27168-rough-idle-sometimes/ 

Could it be throttle body issue? 

https://www.google.com/amp/s/www.audi-sport.net/xf/threads/419589/%3famp=1

7 minutes ago, Steve Q said:

Had a search through the forum, a fellow member had a similar issue and it was the injectors: 

https://www.audiownersclub.com/forums/topic/27168-rough-idle-sometimes/ 

Could it be throttle body issue? 

https://www.google.com/amp/s/www.audi-sport.net/xf/threads/419589/%3famp=1

I think I might whip the injectors out over the weekend and get them tested, and see what the diesel specialist reckons.

3 hours ago, Svensamios said:

I think I might whip the injectors out over the weekend and get them tested, and see what the diesel specialist reckons.

Good plan. Please keep us posted on how you get on 

Right guys, 

I sent all 6 injectors off to be tested, low and behold, injector 3 has zero flow on idle. Got it rebuild, fitted it this evening, and I've got a smooth idle! Took it for a drive, no fault codes and no lights. Low rail pressure seems to have disappeared now too. 

Just want to say a massive thank you  to everyone that gave advise. I can finally get back to work now 😂! 

Cheers once again! 

Well done.

3 hours ago, Svensamios said:

Right guys, 

I sent all 6 injectors off to be tested, low and behold, injector 3 has zero flow on idle. Got it rebuild, fitted it this evening, and I've got a smooth idle! Took it for a drive, no fault codes and no lights. Low rail pressure seems to have disappeared now too. 

Just want to say a massive thank you  to everyone that gave advise. I can finally get back to work now 😂! 

Cheers once again! 

You're most welcome, glad you got sorted 😊