Hello all
I am new to the forum. I have been reading this thread closely for the past few days.
I work at a small independent garage which specializes in European cars. I'm working on a 2009 Audi A4 B8 2.0 TDI.
The engine code is CAGA with a 0AW CVT transmission.
The car came to us as a no-start - the customer was driving the car - when all of a sudden it turned off.
We found the cause to be the ECU gone dead due to water ingress - the ECU in this car is located in a cavity below the wiper cowl on the driver's side (The car is right hand drive - so it was in the right side) - along with a fuse and relay carrier.
We sourced a second hand ECU - coded it to the car, but it's not starting. Gave the injectors and High pressure fuel pump to my injector & pump specialist. It was determined that 2 out of the 4 injectors were faulty and they were repaired - the remaining 2 injectors were cleaned. The High pressure pump was found to be bad and another one was bought.
Next - the fuel tank was drained and cleaned. The diesel filter was replaced. New diesel poured in. Everything was put back together and fuel system bled, but still it was a crank and no start. We found that if introducing a starting fluid (in our case - petrol) - when cranking, the engine would start after cranking for long and stay on - but it would hunt. After putting back the fan belt, and introduction of starter fluid again, engine started after long crank and it stayed on normally without hunting.
I have another Audi A4 B8 with the same engine which is lying here for collision work - to eliminate any faults with the components of the non running car, I swapped over stuff from that car to this one. I'll list them below. For the sake of easier comprehension, I'll refer the non starting car as the "White car" and the starting one as "Red car"
List of components swapped over from white car to red car for testing:
1. Fuel rail (complete with rail pressure sensor and regulator) - red car started
2. all 4 injectors - red car started
3. In tank fuel pump and in line fuel pump (located on the underside of the car - near front driver running board) - red car started
4. Starting kit of the white car (ECU, Cluster, Rear BCM, Key Reader, Key, ELV) - red car started
5. In addition to this, I checked the new High pressure pump on another car (a Skoda Octavia 2 with CLCB engine which was in for a timing belt job) - that car starterd right up with the new HPFP - so the replacement HPFP is good.
Next, I checked the wiring harness of the non starting car - checked continuity of the lines from the ECU to the injectors - all good. Also compared the resistance values of the lines from the starting car and the non starting one - both were similar - so I guess that rules out wiring issues. Another thing I have to add - the throttle body of the non running car was shorted - when plugging in the original throttle body, the scan tool loses communication to the ECU - so that was replaced.
Also replaced the crank sensor - even though I was getting a reading from both cam and crank.
Timing was checked multiple times by different techs. The timing belt is in good condition. There are no timing or co-relation fault codes stored.
No luck - and now the car is not starting even after introducing starting fluid and long cranking.
I closely followed the advice on this thread to zero in the problem. Logged data with VCDS as per the instructions shared here. Also logged the data from the starting car for comparison (I unplugged the injectors in the starting car to simulate a no start condition and check the pressure build up in a no start condition). Found that the fuel is not building pressure in the non-starting car. But I'm baffled as to why this could be as all the components of the non-starting car are working perfectly in the starting one?
Values of the starting car for comparison
Any pointers on where to look next is greatly appreciated!
Thank you
