vems trigger problems on aan

[S2central.net]

Gimme a shout if you need the scope to bottom out the timing issues.

[a4kquattro]

Hi Paul,

And they say Motronic is complicated - LOL... Seriously though - good luck Des... trying to work out if the reference pin needs to be magnetic or not.

no need for it to be magnetic, but it does need to be ferrous. (eg attracted by a magnet)

On motronic the crank reference signal has to arrive within the 'hall window' -

not true in my tests. It will start up to 10 degrees out of window. Found this out when I attempted to convert a car to VEMS here that had a custom flywheel fitted. ran fine on motronic, when I rotated the engine over and checked the position of the reference pin it was indeed fully out of window by 5 degrees. In that case I moved the pin to fix the issue.

looks like VEMs is same in this regard when I skim this thread. Don't forget I still have your sillyscope here - that would be useful here to 'see' what signals you get on a cold crank. I was using it today helping a friend condemn an O2 probe on a 996.

yep, scope would help. if you've got dual channel scope both the cam hall pulse as well as the reference pin. should give you a good picture of whats going on.

Incidentally its probably easiest to do that with engine running on motronic. just "back probe" the pins at the connector with the rubber boot pulled back a bit. works good, BTDT.

[S2central.net]

@marc - I had never tried to see how much motronic would accept there for misalignment - but the reference mark is supposed to arrive within the window. Clearly Mr Bosch designed some room for movement there.

[diesel des]

Update then. So I checked the timing marks and sensors. Everything was where it was ment to be. I swapped the two crank sensors for another set. And now the problem is almost cured! I say almost as when cold there is still the odd trigger fault maybe 2 times a minute.

Any ideas? What should the clearence between sensor and pin be. Cheers.

[S2central.net]

This will be useful for comparison - http://www.s2forum.com/forum/showthr...d=1#post498878

See you tomorrow AM Des

[diesel des]

Ok so now my car runs on VEMS but gets some trigger faults causing PING in engine. Look at the scope. Blue is crank pin, yellow the cam. The 7A flywheel gives 2 small extra pulses before and after the main crank pulse confusing vems.

[diesel des]

And the next pic. Hopefully vems software guys can sort this. looks easy i think...

[Bram]

I have not seen that on my scope using a 7A flywheel. It looks like some metal interference of (maybe) other pins is too near the crank sensor?

[diesel des]

There are no other pins on the flywheel, these spikes seem to be caused by the notches on the flywheel. has anyone pictures of a 7a and a 3b flywheel so I can compare. There is now a vems page for this. vems.hu/wiki/index.php?page=MembersPage%2FDesmondAudi Cheers des

[S2central.net]

Interesting... clearly you are getting some rogue pulses. Motronic must have superior filtering to avoid the rogues. It would seem that VEMS is purely triggering on the pulse edges, but if it also had a pulse threshold detection that would nicely filter out the rogues.

It should also be possible the create an external circuit that pre-processes the G4 pulse to clean it up before the VEMS ECU. Analog stuff isn't really my bag, but I would be drawn to some sort of comparator circuit with a threshold level that is used to gate the good pulse... Look at difference in voltage of the good and bad pulses. It might even be worth using a potential divider to reduce the amplitude on both pulse types - this might bring the rogue pulses inside a window where they are correctly ignored by VEMS... whilst keeping the good pulses large enough for healthy detection.

Aren't oscilloscopes brilliant though !!!!

[A80Avant]

Des, if it makes a difference, that pin looks definitelly bigger than the piece we made on my flywheel. BUT i cannot be sure if that could cause the problem, as this is something completelly new here.

i aggree about the trigger setting. Mine is set to 58 as well, although on older version (1.1.27)

[a4kquattro]

Ok so now my car runs on VEMS but gets some trigger faults causing PING in engine. Look at the scope. Blue is crank pin, yellow the cam. The 7A flywheel gives 2 small extra pulses before and after the main crank pulse confusing vems.

and you have a cam hall inverter? You'll get extra pulses without one for sure.

[diesel des]

This is great feedback guys. Ok Marc, yea both the vems ecu's have the cam invert BUT on the wiki page the guys are now saying that it might cause a problem. What ya think??

http://www.vems.hu/wiki/index.php?action=edit&page=MembersPage%2FDesmondAudi

Paul, yea im sure the input could be processed to help vems out, but thats yet another box of bits which i could do without. And vems is ment to be a simple plug in setup, even with the 7a flywheel, so i think the software can be sorted to deal with this.

Jamo, thats interesting about the teath setup. I will ask Peter my supplier to confirm. Also will check about the injectors.

Cheers guys.

[S2central.net]

If vems is plug and play then why is hall cam signal inverted ?

[diesel des]

Found a picture of the 7a flywheel and clutch setup. Clutch i got from Marc and is gooood...
I welded the extra steel on the pin after these pictures.