I am suffering from starting issues which tend to resolve by priming. J presume a sender pump fault. No errors are shown on vcds.

Does anybody have details of the pump used in the oump and sender unit. I would like if possible to swap out only the pump.
 

Asz engine so 1.9 tdi 130bhp

There is an issue where something fails on the pickup (I think its possibly a seal or o-ring maybe) and allows air to get in. Usual symptom of that is its fine if the tank is full, but problematic once it gets lower down. There has been posts on here before about that, or have a look via the access hatch?

Also issues with the fuel filter if its been disturbed recently might account for your issue (air leaking in through fittings).

Priming it again suggests your getting rid of air, the air has to get in there somehow.

Thermostat T piece O rings on filter can be problematic.
Injector seals and tandem pump can also cause issues.
I had problems with mine that I traced to the injector seals I think it was.I temp fitted some clear fuel hose on engine to prove air in system after being stood for several hours. I then did some clamping of hoses to see where the issue was. It's been several years so can't remember exactly where I clamped but return line between filter and engine and also after filter on return to tank rings a bell. There might also have been one between tandem pump and head at one point? Sure some Googling will find a write up think I found something on a VAG site.

The key with the o-rings is to always use a Bosch filter

He he

Thanks for all the suggestions. Whilst I think air ingress may be occurring as I can hear a wooshing noise from the pump, it was not what was causing the non starting issue. That said from the filter to the IP there is no apparent air ingress. I had swapped it over for clear 7mm hose.
I opted for a new pump/ swirl pot because the original seemed to only be working intermittently. However that was not the issue and the problem continued. YEsterdayt i broke down completely. no way to get her started. I noticed the glow plug light didn't come up on the dash this pointed me to the culprit, the 109 ECM & pump relay. It was clicking but only letting a max of 2v through to the high current load terminal. .       

johnnyroper, could this be the guide you referred to: https://pics.tdiclub.com/data/517/PD_fuel_delivery_check.pdf

oh no, where did you break down and was it all safe and ok?

here's hoping it's just a relay

Quote from: SirDavidAlhambra on May 11, 2022, 01:47:27 PMoh no, where did you break down and was it all safe and ok?

here's hoping it's just a relay

All was safe. Parked up safely to drop my son at school, when i got back to the car and it wouldn't start no matter how many times i primed/ turned the key. Towed home, with the new relay, it started straight away. As soon as i turned the key I could hear the pump prime.

Phew, a broken down car is one thing, but safety is another. So glad to hear you were all safe and well, not put in any danger