Audi s2 3b won't start PLEASE HELP

[Mikes2]

Not on a 3B

[Stealthacq]

Can I ask:
Speed g28
Contact 1 Blue to pinout 48
Contact 2 gray to pinout 47
Contact 3 sheathed ground pinout 10

Crank sensor g4
Contact 1 red pinout 48
Contact 2 purple pinout 49
Contact 3 sheathed earth pinout 10
I know the connection earth's are 10
But connection 1 on both sensors are connected into pinout 48 is this the signal wire or the 4v supply?
As if it is the joint signal wire this would mean the ecu is not powering up the crank sensor?
It just seems odd that If it was a joint 4v supply cable they would both be powered seen as there is no faults with the wiring
Cheers

[twoqu]

Both these sensors generate a signal (V) from either the pin or flywheel teeth. So they are not powered by the ecu.

[Stealthacq]

So when I get 4v Down the speed sensor gray when ignition is on is this right?
Thanks for the help mate

[twoqu]

Thats a good question. I am going to say yes as its dependent upon how close the sensor is to the tooth on the flywheel. Obviously with 135 teeth you are more likely to get a signal then one pin.

[twoqu]

http://www.s2forum.com/forum/showthread.php?t=30947&highlight=motronic+signals

You are gong to have to read between the lines as the engines differ but in principle the signals are the same.

[Mikes2]

Some of your colours / pins are mixed up

http://s2-audi.co.uk/workshop/schematics/motronic_3b/page3.png

G28 is grey and the pins are

Pin 1 (grey wire) -> ECU pin 48
Pin 2 (blue wire) -> ECU pin 47
Pin 3 (black wire) -> earth connection in ecu wiring loom

g4 is black

Pin 1 (red wire) -> ecu pin 49
pin 2 (lilac wire) -> ecu pin 48
pin 3 (black) -> earth connection in ecu wiring loom

[Stealthacq]

I Recon its been messed about with for the previous immobiliser!!
The gray cable was crimped with another wire and the same wire crimped back into the correct terminal.
I will check tomorrow as I do think it's all a bit odd
Cheers ��

[Stealthacq]

So if I get the crank sensor on the pin I should get 4v?

[twoqu]

Perhaps you have not spotted this tucked away on that linked thread:

https://www.picoauto.com/library/case-studies/audi-s2-intermittent-and-progressive-failure-to-start?A080701

Interestingly it states that the injectors were not being triggered despite the fuel pump relay being energised!

[twoqu]

Going back to the V down the grey cable with ign on. To be honest I am not sure about that!
If the engine is moving then an A/C voltage is produced by the sensor. So if you have a 4V dc signal that seems a bit strange and its not mentioned anywhere I know of. It does seem that some manufacturers use a bias signal for fault identification and as we know the speed sensor fault appears if the engine has not been cranked. Whether thats connected I know not! Perhaps someone can verify that.

[twoqu]

As both sensors are identical in design apart from the color of the plug and are interchangable then the pin assignment should be the same. Not sure thats reflected above.
Two wires are common which are the earths(pin48). The signal wires are either side (47&49). The other wires are for the shielding.
So if the grey is the sensor earth then I cannot see why it would have any voltage on it. The signal wire will have A/C voltage on them when engine is cranked/running.

[twoqu]

It does look like that schematic has transposed one speed sensor.
1 is the common earth.
2 is the signal wire.
3 is the shielding earth.
So they should be mirrored.

I have just checked and there is continuity between pin 48 and 19 on the ecu. So that does make them earths.

[twoqu]

I also remembered a previous discussion!

http://www.s2forum.com/forum/showpost.php?p=924443&postcount=23

[Stealthacq]

It looks like all the pinout for the crank and speed sensor is mixed up so Al be checking them.
Bit confused as it does not look like the pinout have been changed.
Al be checking tomorrow and looking faward to the ecu coming back as ok
Cheers guys