G4 & G28 Signals

[S2central.net]

After chatting with Diesel Des today about the timing issues he sees on VEMS at high revs because the G4 reference pin is so small on the 3B flywheel, thought I would post up a pic of scope output that I snapped yesterday on my stock ABY flywheel.

That is a 30V pk-pk pulse on G4 and 15V on G28 as well. Apparently the 3B crank pin produces a significantly smaller spike and VEMS can struggle to detect it 100% reliably.

[rj scotty]

could the 3b pulse be amplified electronically before its sent to the ecu?

[diesel des]

Yes it could. I will post pics of the 3b signals when I put the scope on it this week. I need to confirm the sensor to pin gap on mine.

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[quattro-nick]

or this is a solution
pictures of my AAN engine with 3b flywheel

[diesel des]

Yep that looks much more substantial than the stock small pin.

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[S2central.net]

Looks pretty much exactly what you were talking about Des... would be good to see before / after results on your scope.

[S2central.net]

could the 3b pulse be amplified electronically before its sent to the ecu?

A good bodge to try might be a little passive transformer with 2:1 voltage gain on the output side so it steps up the smaller amplitude pulse coming of the G4 sensor.

[diesel des]

I will definitely scope out the signal before I mod anything. I got a crank sensor from another vag car that is slightly smaller diameter and is longer so should be easier to fine tune it's position to exactly were it needs to be.

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[diesel des]

Last night I fired up the scope and had a look at the signals. On the pin sensor g4 I only have 2.5 volts! As the revs rise this increase but the waveform seems to distort around the point I get the missfire. Also it's a smaller signal on the negative half of the cycle if that makes sense.

This is the idle pic



So I fitted another sensor which is slightly longer and from another vag car. I measured the pin to sensor distance with blue tack and I was about 3mm away. So with the new sensor I reduced this to less than 1 mm.

The result was 5 volts on the sensor but still the distortion at higher rpm and the loss of trigger in vems. I played with sensor position a bit more and then the car died. So I have most likely damaged the pin or sensor. As I'm doing the clutch soon I don't care.

Again it seemed to be the negative part of the wave that was being distorted so I tried changing the 2 wires around at the sensor plug. This gave vems the shits and the car would generally mess around and get poor triggers.

Interestingly I found if I connected the scope with its center pin first and it's shield or ground second I would also generate a load of trigger errors due to the induced emi. So it seems vems is sensitive but the sensor needs a solid piece of steel near by to get a really strong signal. Maybe vems is loading the circuit and hurting the voltage.

Anyone have a circuit diagram for this part of vems?

Cheers des





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[diesel des]

Unfortunately it's not my usual scope and I actually had problems getting it to reliably trigger on the signal so was unable to get a pic of the distorted signal.

I did put the cam sensor on channel 2 and the g4 pulse is were it's ment to be eg within the cam pulse. There are 2 g4 pulses for every cam pulse.

[UrS4boy]

G4 Crank Position Pin Location and Size info

Here is some info about the stock G4 crank position pin (which BTW has been known to fall off):

G4 Pin info: http://forums.quattroworld.com/s4s6/msgs/51259.phtml


Photo courtesy of V6quattro here.

[S2central.net]

That is very weak alright. Weird that my G4 goes negative first and yours doesnt - what pin did you have 0V on scope connected to ?

[quattro-nick]

@ diesel des:
by a AAN/aby engine you need to change the pins in the crank sensor connector before using vems
be sure that's done
it is described in this link:

http://www.efiexpress.com/catalog/ar...?articles_id=1

[diesel des]

Cheers guys. Paul I can't remember. There is a red and a purple wire at the loom connection on the g4 plug. The other black wire is the shield.

I will start and pull the gearbox tonight. I will make a steel part up at least to the dimensions in the pictures above and weld that on. Then carefully set the gap to just over 0.5mm.

It ran great on the last 3b flywheel but everyone seems to be a bit different Ffs. Wondering as this one has been balanced is there a balance hole nearby which is distorting things. If there is I will use the other non balanced flywheel that ran before ok.

Also as this is a stroker build there was no machined place on the block for these 2 sensors so I had to drill grind and tap them. But there does seem like there is less gap between the toothed part of the flywheel and the g4 sensor as the g4 sensor has some slight marks on its side were its been touched.

The block casting is slightly different in that area and I don't want to grind too much and **** something up big time...

[quattro-nick]

maybe this is also useful

http://www.s2forum.com/forum/search....archid=3043100