No start after fuel filter change

**davidmac** · 02-07-2010,10:02 PM

Help I changed the fuel filter after being dogged by constant rough running.Car is now refusing to start.Ran a diagnostics check with no stored codes coming up.There is no electric pump on the car just a mechanical pump driven from the cam shaft.I am starting to think the lift pump is away.Is there any way of testing this.Thanks Davy

**Crasher** · 02-07-2010,11:38 PM

A2 what?

If it is an AMF 3 cylinder TDI, they do not have a lift pump and take an awful lot of cranking to get them going after a filter change.

If it stated and ran for about 30 seconds after changing the filter, it will just take around 5 minuets of cranking to get it going which does the battery and starter no good at all.

I use a vacuum pump to pull the fuel through, VAG recommend filling the filter with clean new diesel to speed up the process.

**davidmac** · 03-07-2010,03:31 PM

Hi there sorry its a 3 cyl 02 1.4tdi AMF.I have changed the fuel filter many times before and never had this happen.I have cranked the engine till the bat is about flat nowt.I have pushed the diesel through using an electric pump and still nothing.I did this using the flow and return at the tank.I even monitored the return using a glass to make sure all the air was out before reconnecting the fuel lines.When the lines were full I tried cranking again to no avail.I have spoke to Audi and according to them there is a mechanical pump on the end of the rocker cover taking its drive from the cam.I have checked this out and there is some kind of pump with two fuel lines going to it.I have traced these lines by eye to make sure they are actually fuel lines.There does appear to be some sort of switch/sensor in the line just before this pump.I was wondering if this some sort of crash cut off type switch.Hope some of this info helps.Cheers Davy

**Crasher** · 03-07-2010,06:33 PM

The pump on the end of the head is called the “tandem pump”. This draws fuel from the tank and delivers it at medium pressure (around 3.5 bar at 1500rpm) to the injectors which then pressurise the fuel to inject it.

In your case, I would give it a sniff of ether to see if it fires up, if it does you know it is probably not receiving fuel from the injectors although the cam timing being out or the cam hall sender signal being wrong can cause a non start. Did you do anything else at all other than the fuel filter at the back?

What year is the A2 and if a 2002, does it have the early complete replacement filter unit or the later cartridge unit? Can you do a fault code read?

The sensor in the line is a fuel temperature senor (the wiring has a habit of snapping) but this will not affect the starting like this.

**davidmac** · 03-07-2010,07:53 PM

The only thing I did was the fuel filter.It is the complete unit and not the cartridge.The car is an 02 2002 model.Like I say I have done the filter many times before and never this much trouble.There are no stored codes either

**Crasher** · 03-07-2010,09:45 PM

I think the problem will lie with the T piece temperature regulator valve on top of the filter, perhaps the O rings have become distorted and are allowing air in.

**a8 tech** · 03-07-2010,10:28 PM

agree with crasher, air is being drawn in/pressure drop

**Crasher** · 04-07-2010,12:27 AM

Hello old man, where have you been?

**a8 tech** · 04-07-2010,07:07 AM

Still here Crasher but I have been so busy lately lots of problems causing brain drain, hope your well and busy with profitable work.

**davidmac** · 04-07-2010,12:21 PM

Originally Posted by Crasher

I think the problem will lie with the T piece temperature regulator valve on top of the filter, perhaps the O rings have become distorted and are allowing air in.

Many thanks for all the helpfull replies I will change the o ring and see if that makes any difference