Faulty lambda probe?

[wjam]

Hi all,

3.0tdi BKN cuts out when hot...

I measured the lambda on measurement block 40 today and also logged it over a drive.

Car warmed up etc.

Lambda voltage always ZERO block 040 item 2.

See attached image

So am I correctly diagnosing that? I mean I know the lambda should give 0.2. to 0.8V but am i looking at the right measurement block??

cheers

WJAM

[wjam]

Just caught the engine cut out with VCDS. see attached pic.

The air mass does not react to demand (almost no response) but the oxygen % number on lambda (block 40) rises just after I give a bit of throttle... Right after this the cars actual high pressure fuel reading linearly drops until the engine dies. The demanded pressure remains constant.

The lambda voltage is always zero.. and basically I have no idea if block 40 lambda V is the correct one to read.

So for me (and I will consider any reasoning contrary) either the MAF and/or the Lambda are faulty. The MAF is sticking out here cos it never meets the demands of the ECU. Or the lambda is making stupid demands and the MAF reading is correct... but can't / won't do what the ECU says??

BTW... When the car is cold the MAF requested and actual values follow very closely and gradually deviate over time. Always worse in hot ambient temperatures..

Just remember Audi dealer has just quoted me for 2.5k euros to replace the pump and an inlet swirl flap!!!! but haven't even looked at the MAF and lambda

ciao

WJAM

[wjam]

also on PDF as the picture above is nearly too small to read

ta

WJAM

[wjam]

Update:

I also have occasional bubbles in the fuel line to the high pressure pump!

That might just cause some issues.

What do you all think out there on t'internet

WJAM

[wjam]

Anyone?

Pleeeaaaassseee

wjam

[patrickhorton]

I'm no expert but spend a fair bit of time decifering VCDS traces for my car. But here are my suggestions.

1. Are you sure you have the correct meas block for Lambda? There a loads of blocks called Lambda but they are for other things such as duty cycles of actuators. I refer to some VAG software which gives a definition of each block for the specific model of car/engine. I suspect it is different for each car and the VCDS text is just a guide. If you aren't sure perhaps I can find the actual meas block for Lambda for your car.

2. First impressions are that something is killing your fuel pressure. (the bubbles?) I have not looked at this meas block before and not sure exactly what part of the fuel system the pressure is refering to. The rpm is steady(ish) while the pressure falls and when it gets below a threshold I guess the ECU cuts the engine. As the high pressure fuel pump runs off the camshaft, pressure should be steady at fixed rpm and fairly constant fuel flow.

Good luck
Patrick

[wjam]

Hi,

Agreed... the pressure reading is on the high pressure side of the pump. 270bar normally at idle.

The weird bit is that periodically you hear a change in the engine note a little and that corresponds to a pressure of 440bar, but same RPM 750 approx

That is whats leading me to the air mass or lambda. As opposed to the high pressure pump that Audi are mad keen to change ASAP for lots of cash.

But again, I agree on the lambda, there are quite a few blocks concerned with it and maybe the 0V is simply not used. The very next block does read a voltage which jumps about just before the engine cuts.

I tried erwin for the test procedure but got russian . see separate rant

Anyway, I have a new air mass meter tomorrow so that'll verify that (or not) but at least I'll see if the read air mass follows the demand (which I would expect.

ciao

WJAM

[wjam]

forgot to mention... I find it weird that they choose monitor the high pressure side but not the low pressure side, which would be very useful at this point.

Does anyone recommend a gauge for measuring that?

ta

WJAM

[wjam]

Right.. Air mass meter changed.

Car much quieter and the requested follows the actual pretty close now.

EXCEPT at idle when hot... And furthermore the AC seems to cause all the damage.

It's like it's not able to handle the load of the AC. If i switch the AC off the diesel high pressure value rises to 280 bar and stays stable

Any ideas on that then?

I have to say everyone's very quiet on this type of fault... Please any advise welcomed

ciao

WJAM

[wjam]

Stranger and stranger.. the mystery deapens.

So I return from a run after fitting new AMM. All seems great. Stop and idle for a bit. Bleuuuw. Engine stops as before.

Switch off air con, engine keeps running at a higher fuel pressure than requested.
280bar vs 227 requested
Switch on air con pressure drops to below requested and keeps dropping.. switch off air con back to 280 bar... stable.

Stop car clear codes... do some reading on t'internet, come back 10 minutes later.

Start car no problems requested fuel pressure 227 actual 227. Put on AC same.. no problem.. WHAT. 10 minutes ago it repeatably cut the engine, now it works

BUT.. I notice the air mass requested and actuals are identical.... however as the car runs for a bit the ECU is demanding more and more air mass!! When it quit the requested air mass was 570 odds and actual 400 odds. This is when things start to go mad and I go madder.

So:

Lambda probe engine block 044 (see attached pic)

2 Lambda probe electronics reading 10001001

which according to the list I have here from A8 tech (thanks!) shows system fault (the middle 1 in the row)

Furthermore

3 lambda probe plausibility check usually 0 but occasionally shows 016 "oxygen concentration zero"

Does anyone have a clue on that?

I really need some advice on this lambda because i'm up "la riviere de merde sans palette" until erwin fix their language bug

ta

WJAM