RS2 not starting, VCDS G4 no signal intermittant

[blux]

I'm trying to get my RS2 running, but it's not firing up. Using VCDS I get an intermittant error on the G4 pin on the flywheel.

I've checked the pin on the flywheel and checked the distance from the sensor. It's 0,9mm away. Found online it can be max 1,25mm so should be close enough to trigger.
Also checked conductivity from the wiring from engine bay connector to pin 47 on the motronic 55 pin plug.
Swapped sensors with the G28. After that VCDS gave both G28 and G4 no signal error after cranking it a bit. This was not an outcome I was looking for with this as now both gave an error. It was not clear to me that the G4 was faulty.

Also unplugger the N75 as a test and VCDS picked it up after cranking that is was missing that one.

I found in some documentation that fuel pump relay will not be powered without this signal? correct? I've jumpered the relay and pump runs and fuel rail is under pressure. So I assume these are ready to go but wait for the G4 pulse to come to life.

Also checked G4 flywheel pin with the camshaft sensor. When the pin is at the G4 sensor location the gap for the camshaft sensor is at the sensor. This looks ok to me?

I found that the same sensor is also used on a 7A engine. So Plan for tomorrow Is use that one to have one from a running engine to verify.

Are there any other things what I can check?

[blux]

Some more testing done. G4 sensors swapped between RS2 and audi 90 20V -> audi 90 20V starts as before. RS2 now gives G4 and G28 fault through VCDS.
I've checked schematics and they have a common ground. Next plan is unplug the motronic and sensors to check if there is a short to ground on the G4 and G28 signals.

Other ideas also welcome

[Mikes2]

Fuses - think it will be the ones under the plastic Moteur cover

[blux]

Fuses all checkek pulled one by one.
have just unplugged the motronic connector and g4 and g28 plugs. On g28 all seems normal. G4 the shielding ground on pin3 and signal on pin2 conduct. So i need to go through the wiring to find the short. As g4 and g28 have a common ground from ecu this shorted signal could be the reason for bith of them showing errors in vcds

[JOSH,S ABY S2]

I had similar the other week it was a corroded terminal in one of these plugs.

[Error404]

G4 & G28 share the sensor ground and shield ground at the ECU.
ECU is grounded on the engine block.
You can check signal-in continuity and for short to ground on the signal-in pin/wire.
If you have a scope you can also check signal-in at the ECU connector.
You can also do a sanity check on the G40 with an LED at the connector.

Do you have after-market security / immobiliser on the car?
Sometimes these are installed in odd ways and are often the cause of strange intermittent non-start

[blux]

Engine starts g4 signal was pulled to ground. Solved the short and it fired up

[Error404]

Great
Where was the short?

[blux]

The short was in the engine bay on the cable before it entered the insulation where alle cable from engine go to the inside. The cable is a 2 wire cable with metal shield. It runs as one piece from the firewall bracket to the ECU. At the ecu the shield terminates and the ground for the shield runs back in the direction of the engine. I assume shield ground bundles sonewhere in the loom and takes ground at the fusebox. Only signal ground and signal go into the ECU.

[Error404]

Good find
From memory the shield is spliced with G28 and knock sensor shields also, and ground to an ECU terminal