Camshaft position sensor as RPM source?

[carl0s]

Hi.
Just noticed my KME Nevo isn't reading RPM (unless OBD is connected).
I'm using the same connection (ignition coil if I recall correctly) as I used on my Stag 300.
Anyway there is also the option to use Camshaft Position Sensor as a source, which is recommended for valvetronic engines apparently where the ignition coil might stop on overrun, or something along those lines.

I'm just wondering.. Should I use the intake or exhaust cam sensor? and why is it not the crank sensor instead?

[scottyf]

Wouldn't crank sensor turn / Fire twice as much as a camshaft sensor.
I've only used RPM sensor based on a coil.

Crankshaft sensor on the Alfa I did would be a right pain to get to.
I always though the coils fired even on over run anyway.

[kbs]

Cam sensor as its a nice slow 50% (constant amplitude) high impedance sqaure wave from a hall effect rather than a fast wobbly dirty sine (low impedance, varying amplitute and a missing tooth) from the inductive crank sensor?
If thats the only reason then either cam sensor will do.

[carl0s]

The software works out the divider based on you telling it the RPM as it monitors the sensor.

If the crank sensor isn't a hall effect sensor then I guess that explains it!

[LPGC]

Agreed with everything above...
But you shouldn't have to connect the rpm wire even on Valvetronics?
Nevo doesn't allow setting dividers or trigger voltages related to ignition coils etc, it only has the option of 'not connected / rpm sensor / petrol injector / cam sensor.. With cam sensor it does allow setting of a divider?
Counter intuitive for an engine to cut off ignition even on over-run... better that any fumes etc that might build in the cylinder while it's getting no fuel are burned off rather than causing problems such as detonation etc when the cylinder next gets fuel and a spark, same from an emissions point of view too.

Simon

[carl0s]

Actually it is working from the ignition coil.. It reports RPM twice in the readouts, and I was looking at the OBD area!

According to the manual, it asks you to input the current RPM when you select Camshaft, and it utilises this to work out a divider.

[carl0s]

I can confirm that on overrun, a few seconds after the injectors stop, the ignition coils also stop firing, and the LPG system (KME Nevo) shows "IGNITION". It switches right back on though as soon as coils start firing, so I'm not sure if it matters? Maybe it's OK because I have hot-start enabled.

Either way, camshaft sensor would be a better RPM hookup on this BMW N62 engine.