a3 1.9dti air in fuel problem

[ianrudge]

Hi everybody, obviously new to this but here goes....., diesel - poor starting on cold start, also if left standing more than a few hours. noticed loads of air bubbles traveling from fuel filter towards pump/engine- air getting in from somewhere? also it appears filter is syphoning out after engine is switched off- maybe back to tank, not on the floor. since this initial post i have checked the fuel lines and connections in the engine bay can't see any obvious problems but the amount of air coming through the clear pipe is a lot.

[ianrudge]

We've since isolated the fuel filter, connected flow and return with two bits of clear pipe to see what happens. Result, no more air. So, it's either a faulty fuel filter or the 'o' rings on the 'T' piece. As for the cold start, we will see what tomorrow brings.

[ianrudge]

The cold start problem remains, the air has gone but it wasn't causing a problem anyway. The glowplugs were new but we tested them anyway, all OK. We know the glow plugs aren't needed when warm and when you test there is no power to the plugs when you turn the key(but not start). Again we'll have to wait untill the engine is stone cold, there may be a problem with the glow plug timer. We're going away for a few days, we'll try again when we return.

[ianrudge]

The saga continues, the glow plugs work fine for a cold start, albeit for a few seconds only. The non-return 'T' valve in the top of the fuel filter was buggered (it didn't one way all the time, a known problem) and was replaced along with a new filter. The air has now gone completely. The cold start problem has not. we are now targeting the fuel pump. There is an electric fuel pump bolted to the injector pump, we can hear it doing something but can't remove it because of one odd screw. This pump is also on a timer but we need to test it to see if it generates enough pressure to enable the motor to start, we will let you know in due course.

[ianrudge]

That that we thought was a pump on the injector block wasn't a pump at all but some sort of electrical device. There is no low pressure pump on this vehicle, Audi said it was in the fuel tank, they were wrong. We have decided that there is some air leaking in some where between the injector pump and the injectors themselves. We have replaced the soft fuel return piping but to no avail. a more thorough inspection will follow in a week or so.

[seventh-heaven]

What are the symptoms of the cold start problem? Cranking and not firing, sort of firing, smoke?

[shooey88]

does the car suffer from poor running? misfiring?

[ianrudge]

In reply to Shooey88, Once it starts it runs just fine, no coughs, no splutters, perfect.

In reply to seventh Heaven, If you crank constantly it will take about 10 seconds to fire. But what we have found is that if you turn the motor over 2/3 times, turn off the ignition and then recrank it will fire off the key. The smoke comes when it splutters into life, a lot more if you use the constant crank method, a lot less if you use the latter method. The battery is good as is the cranking speed.

Thanks for both of your replies, it's to ruddy cold to mess with it at the moment

[seventh-heaven]

Sounds similiar to the problem I believe I have - similiarly too cold to do anything!!

If the static timing on the fuel pump is not spot on you will find that it will not start well particularly when cold. Once it has fired and is running the dynamic timing takes over so it will run fine. When cranking the timing of the fuel into the cylinder is controlled by the mechanical timing of the pump. If it is not spot on it will not be fired into the cylinder at the hottest point and hence struggles to kick off.

Last time the timing belt was changed on mine I did not have the time to do it so got the local place that I go for MOT's to do it for me. I suspect that they don't have all the correct timing tools and have not put it back spot on. All in all after this problem and the bill!! I will be doing myself next time!!

[shooey88]

i got a feeling its the starter motor faulty drawing too much current at a educated guess...how u getting on? found a solution?