Audi A4 2.0 TDI BPW Cab - G28 Engine Speed Sensor Implausible Signal

[brasiliangringo]

2008 2.0 TDI BPW A4 Cab - 80k

16705/P0321/000801 - Engine Speed Sensor (G28): Implausible Signal

Implausible signal G28 engine speed sensor rough running / engine cut / buck and some black smoke above 2k rpm with glow plug flashing around and above + 2k with aforementioned symptoms - settles back down fine when you lift off - some 128 faulty injector signals mentioned in measuring blocks but suspect thats the G28 causing it.

Engine starts and idles fine.

- Checked G28 engine inductive speed sensor wiring to/from ECU to sensor / checked relucter wheel for integrity - no missing teeth and running true / not loose
- Both G28 and G40 camshaft hall sensor have been scoped and are being measured correctly. (also checked timing teeth on cam sprocket are not bent)
- All earths in engine bay good with low resistance 002 Ohms.
- Checked fuel pick up up
- Clamped return hose of tandem to build pressure as didn't have the correct pump pressure tester but made no difference to symptoms.
- Checked for signs of oil in filter.
- Boost leak test
- Compression tested
- Intake checked for blockages / MAF functioning
- Actuated EGR and V719 flap with both removed to confirm movement and clean enough
- Checked intake and clean enough
- Injector deviations -1.29 / 0.5 / 0.5 / -1.27 (something like that but within spec) torsion value -0.5.
- Timing has obv been physically confirmed in the beginning.
- Swapped in a 2nd hand donor ECU i have.


I should add the previous mechanic confirmed injector wiring loom with overlay harness and the car came to me with his diagnosis that the cam was worn (which i confirmed) and i have now changed with genuine Kolbenschmitt / bearings and lifters yet before and after symptoms remain unchanged with exception of injectors now being in spec (one of the injector lobes was visibly worn and outside tolerance and on removal bearings showing copper etc) but truth is this is not whats causing the main issue.

I feel i have pretty much ruled everything out except injectors - i think.... but am getting so frustrated i cannot get a good positive fail on anything but obv i am missing something! Any fellow mechanics out there with an opinion please chime in as i need some fresh eyes on this. TIA.

[brasiliangringo]

Can anyone explain this. I thought i understood how the crank inductive sensor worked but this throws me. both are positive at the ECU (and the two right wires merge per diagram) yet with key on yet there is an an earth (132) on the same positive two right hand wires (bl / sw are clipped together and join li / gn to t60/43) Just cant make sense of it..

28918

[Alan02]

The earths being connected wont be an issue as the ECU is picking up a generated signal and interpreting it from the strength of the signals. When you scoped it, where all the Amplitudes the same? As even rust or a small chip on the reluctor wheel can cause a signal the ECU cant process.

[brasiliangringo]

The earths being connected wont be an issue as the ECU is picking up a generated signal and interpreting it from the strength of the signals. When you scoped it, where all the Amplitudes the same? As even rust or a small chip on the reluctor wheel can cause a signal the ECU cant process.

I am going to look into it again as i wasn't the one scoping it but a good double check to do although i have physically inspected the reluctor wheel and believe it to be sound and know the sensor is new - this is an intermittent problem which doesn't tally with something amiss with wheel or sensor as would be a constant issue i would think as cam and crank speeds are being correctly measured i.e. G40 cam speed exactly half G28 up until it starts cutting around 1600 onwards give or take, then the difference can be seen i.e. goes from correct 0.5 to around .49 etc if you are to work out the difference between the two RPMs - at which point obv torsion value goes to 0 as do injector values as its all out of range.

I have now also tried another overlay loom, not sure if that was mentioned in 1st post..

The mystery continues..

[brasiliangringo]

I scoped it again today with my new kit and after spending as much time figuring out the PC GUI got it set up and the wave form was clearly not right despite what the previous tech confirmed but mistakes happen so i am not gunning him. On 2nd visual inspection coming in at an angle via borascope i can now see 2-3 teeth are bent inward and as voltage increases at higer rpm so engine cuts as disparity amplified. Previously i borascoped perpendicular and thus could not see they were slightly bent.

Sump removed and bent 3 teeth back - the blurred photo shows before - you can make out 3 very slighly bent inward upto 1mm or there abouts. One of the rivets holding wheel to back of crank had sheared (see other pics). Plan to put a very hot spot weld in to stop other end ever falling out, replace sump and check. Failing that it all starts getting rather more expensive.

[brasiliangringo]

It worked - car back up and running :)