2.5 TDI AYM engine Hard starting now wont start

[westfield1962]

Hi All

I have been reading a lot of posts on hard starting wont start probs and having the same prob's myself.

Just compleated a full top end re-build on my A6 and still having a few issues.

1. A lot of lag at low speed wont pick up without putting the foot down.
2. Harder to start and bubbles in the fuel line
3. Low fuel consumption 20 - 21 MPG on comp (before re-build 23-24 MPG

Checked out the lag and found that the injector with the sensor was faulty and replaced it slightly improved the lag but increased the MPG back to 23-24.
Then the starting got even harder in the mornings and like others my car is parked in the drive in at a slight uphill angle so i decided to change the fuel filter, when i took it out i drained it into a container and found that there was not very much fuel in it, put the fuel into the new filter and replaced tried to start but will not start, so checked was there fuel being lifted to the filter an found there was not, suspected the pump in the tank so checked to see was the pump drawing current, with the ing on no current being drawn, when cranking battery curreny, no noise from pump, replaced pump and now still the same wont pump fuel to filter. Should the pump freely pump fuel when disconnected from the fuel filter with the ing on or dose it need to be cranked? Is there a inline filter back near the tank that may be blocked?

Any help greatly appreciated

Thanks

Gary

[snapdragon]

The pump in the tank simply fills a reservoir within the tank.
Do you still get the problem with a full fuel tank.?
The BOSCH VP44 on the front of the engine does all the sucking.
Try replacing all the thin braided pipes between the injectors and the one that leads to the injection pump. These can become porous and allow air in. When the fuel is still cold, the valve on top of the fuel filter recirculates the unused diesel and so it can get aerated until the diesel is hot, and then it is sent back to the tank. The pipe to replace is 3.2mm dia and should be about 70p a metre at a motor factor.

[westfield1962]

The pump in the tank simply fills a reservoir within the tank.
Do you still get the problem with a full fuel tank.?
The BOSCH VP44 on the front of the engine does all the sucking.
Try replacing all the thin braided pipes between the injectors and the one that leads to the injection pump. These can become porous and allow air in. When the fuel is still cold, the valve on top of the fuel filter recirculates the unused diesel and so it can get aerated until the diesel is hot, and then it is sent back to the tank. The pipe to replace is 3.2mm dia and should be about 70p a metre at a motor factor.

Thanks for the reply, I have been given a bum steer so as I was told by a Audi Tech that the pump should pump fuel to the fuel filter so I replaced the pump at a cost of €300.... any way to ans your Q never fill the tank more than half always think no point in carrying all that weight around with you, so no is the answer. Got some diesel and poured it into the filter to fill it up it took nearly half a liter and filled the inlet tube to the pump as well just going to bleed now when battery is charged back up. Any idea why pump would not suck fuel up and bleed its self? The last time I changed the filter it self bled! Will change the return lines in the next couple of days.

[snapdragon]

I was told by a Audi Tech that the pump should pump fuel to the fuel filter so I replaced the pump at a cost of €300....

The same happened to me!
There is an open-topped reservoir in the tank, which fills by way of an integral pump. Because the tank is an odd shape, it scavenges fuel from 2 or more corners (IIRC 4 with a Quattro model) fills up a chamber which is set higher in the tank. So if you fill the tank up, this whole open topped chamber is submerged anyway and the pump redundant until fuel level drops.

If you try and bleed the fuel without the ignition on by sucking it through, it will become empty, maybe holds about 4 litres.

Someone on here had a leaky new VW genuine filter a few weeks ago and had similar problems.

[westfield1962]

All sorted now bled injectors and started no problem.... funny thing is now the average MPG has shot up to 27/29 from 20/21 for no apparent reason, any ideas any one.

[gordonowusu]

Gents i had the same problem when the in-tank/lift pump was not lifting fuel to the fuel filter. i was having bubbles in the clear fuel line and did all sort of diagnosis but failed to sort the problem.

the problem was niether the pump or the fuel lines sucking air. it was the in-tank fuel pump relay (395) located in the ecu box where the glow plug relay is also located. i changed it and the lift pump now pump when cranking engine. started engine and all bubbles disappeared in less than a minute. is never appeared again when i give it a full throttle.

hope this helps someone