Diesel Knock When Cold

[Overdose]

Good morning, all,
As per the thread title, my A3 has a knock on one cylinder when cold and it seems to be getting worse, either due to the seasonal temperatures dropping, or injector degradation.
I ran a leak off test for 1 minute at idle which gave 2.5cc per injector for 1-3 and 3.5cc for injector 4. This would not show a leak past the nozzle though.
It would seem to me, that one injector is over fuelling until the engine ECU can compensate when warm.
What test can be run in situ, to diagnose a leaking injector?
I have an injector ready to go, but I need to know which one to replace, either 3 or 4. The problem is, that when hot, the injector deviations point to 3 compensating for the others, but the car runs fine and when cold, the fault looks to be on injector 4 and this is when the engine knocks.


The engine is a CFGB: 170BHP 2.0TDi, no fault codes for the engine module.

Logs below, cold and hot...

Wednesday,02,October,2024,08:56:56:38737
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 8 x64
VCDS Version: 24.7.0.0 (x64)
Data version: 20240715 DS356.3
Ross-Tech: Home




VIN: WAUZZZ8P0CA147188 License Plate:
Mileage: Repair Order: Injection cold






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Address 01: Engine (03L 906 018 AJ)


08:56:39
IDE00365 Injection quantity deviation cylinder 1 -0.22 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 -0.86 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.05 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 1.14 mg/stroke


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Address 01: Engine (03L 906 018 AJ)


08:57:17
IDE00365 Injection quantity deviation cylinder 1 -0.18 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 -0.71 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.23 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 1.12 mg/stroke


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Address 01: Engine (03L 906 018 AJ)


08:58:03
IDE00365 Injection quantity deviation cylinder 1 -0.16 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 -0.54 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.27 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 0.98 mg/stroke


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Address 01: Engine (03L 906 018 AJ)


08:59:10
IDE00365 Injection quantity deviation cylinder 1 0.09 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 -0.80 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.28 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 0.99 mg/stroke


and engine warm

Tuesday,01,October,2024,14:14:29:38737
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 8 x64
VCDS Version: 24.7.0.0 (x64)
Data version: 20240715 DS356.3
Ross-Tech: Home




VIN: WAUZZZ8P0CA147188 License Plate:
Mileage: Repair Order: Injector Knock






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Address 01: Engine (03L 906 018 AJ)


14:14:11
IDE00365 Injection quantity deviation cylinder 1 0.13 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 0.21 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.55 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 0.20 mg/stroke


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Address 01: Engine (03L 906 018 AJ)


14:17:46
IDE00365 Injection quantity deviation cylinder 1 0.24 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 0.23 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.66 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 0.19 mg/stroke


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Address 01: Engine (03L 906 018 AJ)


14:17:49
IDE00365 Injection quantity deviation cylinder 1 0.23 mg/stroke
IDE00366 Injection quantity deviation cylinder 2 0.24 mg/stroke
IDE00367 Injection quantity deviation cylinder 3 -0.66 mg/stroke
IDE00368 Injection quantity deviation cylinder 4 0.19 mg/stroke

[Crasher]

Any value even near +1 is bad so new injector 4 and go from there. VAG 03L 130 277 Q at £746.40 or a Bosch 0 986 435 166

[Overdose]

Thank you for that. The injector that I have here is a xxx 855 CX, I was told it was correct after giving my reg No. and some places list this as an alternative. Perhaps these are manufacture exchange items?

Anyway, No.4 injector replaced and figure re-checked, see below.

aturday,05,October,2024,13:52:27:38737VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 24.7.0.0 (x64)
Data version: 20240715 DS356.3
www.Ross-Tech.com




VIN: WAUZZZ8P0CA147188   License Plate: 
Mileage:    Repair Order: Post inj 4






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                Address 01: Engine  (03L 906 018 AJ)


13:52:13
  IDE00365   Injection quantity deviation cylinder 1 0.28 mg/stroke
  IDE00366   Injection quantity deviation cylinder 2 0.01 mg/stroke
  IDE00367   Injection quantity deviation cylinder 3 1.07 mg/stroke
  IDE00368   Injection quantity deviation cylinder 4 -1.36 mg/stroke


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                Address 01: Engine  (03L 906 018 AJ)


13:52:34
  IDE00365   Injection quantity deviation cylinder 1 0.31 mg/stroke
  IDE00366   Injection quantity deviation cylinder 2 -0.01 mg/stroke
  IDE00367   Injection quantity deviation cylinder 3 1.03 mg/stroke
  IDE00368   Injection quantity deviation cylinder 4 -1.33 mg/stroke

[Overdose]

I’m going to consider the knock resolved.
whilst the car undoubtedly would benefit from one or two more injectors, replacing No.4 injector, stopped the diesel knock when cold.