Fuel pump problems on A6 2.0 TDI

[jc4stuff]

Thought I'd let the forum know that I got my 55 plate A6 avant back a month ago from the garage after 6 weeks, as they have finally found out that the fuel pump deteriorates due to disel additives (allegedley).

The symptom was a slightly noticable miss-firing when accelerating, especially at cruising speeds. The 6 weeks were used to first of all change the injectors, then strip the engine, then replace the engine (whole new unit), then finnally replacing the fuel pump. Luckily under warrenty.

Initially they said there was noting wrong because the computer "says so". Getting Audi roadside assist to sit in the car whilst it happened was the only way to get it admitted to.

The Service guy says they have had a few in since then, so if you are experiencing the same, you may want to point the garage at the pump and save some time.

[jazz rana]

Hi,
Which pump was it? The one in the tank or the tandum fuel pump?

[a8 tech]

The tandem pump seal fails and oil and fuel mix,i have commented on this issue before.You either have oil in the fuel system or fuel in the oil which can be easily cofirmined by a high oil level and smell of diesel.This is a known issue and i am supprised it took them so long.Also the best way to determine whats failed is to remove the fuel filter and cut it in half,if there is aluminium in the filter then the injectors are moving in the head(only slightly but over time they grind the seating surface)if metal then the tandem pump has worn.Also there where a batch of tandem pumps with incorrectly seated seals and the fuel pored into the engine and BANG on average 4000 miles from new.

[jazz rana]

A8 Tech,
I have a problem with a A6 2.0 Tdi which starts for 3 seconds and dies.
Volksline (VW specialists) apparently, cannot find the fault, no stored faults, computer says no!

Problem started by loss of power, then getting back from a 500m round trip car was dead by the morning when i went to start it.

Replaced tandem fuel pump, no joy. Any advice/recommendations?

[a8 tech]

Check for oil in the fuel tank.Also carry out a fuel pressure test as possible injector seals leaking.When you say dead do you mean flat battery or no cranking.If the battery is ok and the engine and there are no other issues ie starter then check coolant level as the cylinder heads can develop hair line cracks on cylinder 1,4 and coolnt fills the bore which prevents cranking.Ignore the last bit if coolant level ok.If none of these hold open the egr and throttle shut off to allow air to enter the inlet manifold and see if she starts.2.0 tdi has lots of issues so dont be suprised by various diagnosis routes.Hope that lot helps.Ps if the tandem pump was replaced for fuel/oilmixing then the fuel filter needs replacing and the fuel lines and tank cleaning out as it is possible the oil is still in there and the cutting out lack of power is one of the symptoms.

[jazz rana]

a8 tech,

When i said dead i meant car would idle for 3 seconds then shut down.

The tandem fuel pump was only replaced because volksline (having apparently consulted with Audi dealers) concluded there wasnt enough pressure coming from it. It was a waste of money as the car still has the same fault as before. ie: nothing wrong with original tandum pump. I really dont know how they tested the tandum pump as it needs a running engine to get the pressure!

I have now withdrawn my audi from volksline. Spent all morning getting her back. So now i have a car just for show.

Coolant level is ok. The pump in the tank sounds as if its working fine. Fuel fiter was bypassed still not joy. No stored faults. Weird.

At what point are you recommending doing a fuel pressure test? ie: between pump and tandum pump or after tandum pump? If after tandum then how is it possible to take that reading?

Thanks inadvance

[a8 tech]

The fuel pump in the tank will pump fuel to the fuel-pump at the engine(tandem)at half a bar.If half a bar is found before the tandem pump then this is ok.Once the engine starts the tandem pump will increse the pressure to 6.0 bar and then the injectors increase it again to 1800 bar ish.So the first two readings are important as this is the area affected for start up.If the supply pressure from the electric pump is insufficent then only air will be drawn if insufficient fuel in the lines.Fit some clear fuel pipes from the filter to the tandem pump and watch whats going on.If there is no air and plenty of fuel then check the crank sender signal if this is being lost then the ecu will default to camshaft hall sender and delayed starting as tdc 1 is lost.Refer to dealer as indis are fine with old stuff to a point but dont have the same info and equipment as dealers.I have give you more than most would give you to fix this or locate the fault ie(fuel or engine mangement)i cant help much more from a pc but will guide you.Regards A8

[jazz rana]

Update:
Checked fuel pressures, pump in tank ok, tandem pump is new so that must be working, no air bubbles in clear piping from fuel filter to tandum.

Hence must then be this crank sensor you mentioned in your prior posting..

Where do i find this crank sensor? If all fails after this, its going into Audi dealers. I need the car back on the road asap! ARGHHH!!!

[a8 tech]

look at the oil filter housing and you will see the sender beneath it mounted to the engine block facing the flywheel.You may need to remove the oil filter housing/oil cooler to replace it.

[a8 tech]

one other thing,the egr change over paddle breaks away from the shaft in the inlet and cuts the incoming air off,there are two 6mm alen bolts holding the pipe from the egr cooler to the egr on the inlet manifold,remove the two bolts and push the flap open with a screwdriver and restart.If it runs longer than it has then the fault is there.You can for test puprposes remove the egr on the inlet manifold and run it to see if this lets the engine run .