I have a 2.0 TDI A4 Cabriolet, 2007, Engine Code BPW, 6 Speed Manual.
The problem started when I started her up on Wednesday lunch time and there was a sort of thumping noise coming from the engine area. After further investigation the noise is coming from the air intake where the engine seems to be blowback. See vid below hear:
You will see that although there is the blowback noise there is no shake or judder indicating a misfire. When driving the car apart from the obvious blowback noise increasing under more engine load, there is lack of power and an obvious misfire when accelarating for example from 60 mph +
Following this I called the AA man who confirmed there is some sort of blow back from the exhaust system into the intake manifold. We suspected it could be the EGR valve or possibly a bent intake valve.
I have carried out the following to diagnose the problem, unfortunately with no luck so far.
0: Checked with Vagcom: No fault codes
1: EGR Valve: Removed and cleaned EGR valve, it was dirty but still functioning. (see pictures below)
http://dl.dropbox.com/u/38150502/A4 Misfire/Picture 003.jpg
http://dl.dropbox.com/u/38150502/A4 Misfire/Picture 004.jpg
http://dl.dropbox.com/u/38150502/A4 Misfire/Picture 005.jpg
2: Blocked the EGR with a blanking plate at the flange between the EGR cooler and intake manifold (At Item 19 in link below)
http://dl.dropbox.com/u/38150502/A4 Misfire/Exhaust gas recirculation system - engine codes BKE%2C BPW%2C BRB and BRC.pdf
3: Compression test on the engine - This is a bit of an iffy one where the compression tester developed a leak during the test, Cylinder 1 & 2 both reached 400 PSI, when we did 3 & 4 the compression test fitting broke and only got 300 psi on cylinders 3 & 4. When we repeated the test on 1 & 2 we got 300 psi. (300 PSI is still within the limit according to ELSA. (document link below)
http://dl.dropbox.com/u/38150502/A4 Misfire/Checking compression - engine codes AVB%2C AVF and AWX.pdf
According to Elsa the compression test on a BPW engine should be done using diagnostic equipment, is this on Group 13 on the ECM ? Showing the injected fuel quantity to detect an imbalance ? (Document below)
http://dl.dropbox.com/u/38150502/A4 ...RB and BRC.pdf
I have just ordered a compression tester which should arrive in the next few days.
4: Disconnected exhaust system from turbocharger to eliminate the chance of a blocked exhaust and or DPF (even though showing as not blocked on Group 75 Vagcom). Disconnected from Item 7 in link below
http://dl.dropbox.com/u/38150502/A4 ...ate filter.pdf
5: Glow plugs: Removed and checked, all seem to be the same colour which indicates all cylinders are firing well. See pic below and correct me if I am wrong:
http://dl.dropbox.com/u/38150502/A4 Misfire/Picture 007.jpg
(Left to right, Cylinders 1 - 4)
6: Turned engine over with glow plugs removed to see all injectors are delivering fuel. I could not see any noticeable difference between the sprays, see vid below
http://dl.dropbox.com/u/38150502/A4 Misfire/Picture 008.MOV
7: Checked injector / pump rod adjustor screw according to procedure below, I found injectors 2 and 3 were 1/2 turn loose. Still did not help
http://dl.dropbox.com/u/38150502/A4 Misfire/Removing and installing unit injector.pdf
8: I disconnected the injectors individually to rule out if one of the injectors is not working. Upon disconnecting each injector there was a considerable change in engine noise and noticeable misfire. Indicating that all of the injectors are working. Also at no point did the blowback noise stop.
9: Filled tank with injector cleaner and 20 litres of V-Power and took the car on a 50 Miles run. No difference :-|
10. Disconnected air intake hose at inlet manifold: Can definitely feel the "blow back" from the intake manifold suction.
So here we are, I have asked a number of mechanics for their opinions and the only things I can think of are:
- Bent Intake Valve: To be confirmed with compression tester, however there is no smoke and engine is not shaking or misfiring
- Cracked Intake valve seat: ? Only be checked once head is off
- Leaking Head Gasket: To be confirmed with compression tester, but the pressure on all 4 cylinders is still 300psi which is above spec.
- Damaged Injector Nozzle, where the fuel is not atomizing and only spraying down causing poor combustion. However the vid I posted shows a similar spray. Maybe I should get the injectors checked ?
- Failed seal on injector: however this would result in blowback in the rocker cover and not intake manifold..
I have also read this document below which details how the injection system on the PD engines works.
Any help, views, comments and corrections are welcome. Thanks in advance