pr0xZen

Since I got the car 3-4 months ago ('99 Euro A6 2.4V6 q.avant), I've had starting issues when the engine is warm. It does not gives any codes. It will crank stable and rapid as "normal" for 5-15 seconds, and usually won't "fire up" unless I jog the gas pedal (manual) 1-2 times after the first ~4-5 seconds of cranking.

I recently tried logging a few groups on the engine with VCDS during this cranking, and VCDS lose connection with the module when I crank the engine. If cranking from cold, it will fire up within a second and VCDS usually "comes back" with readings - but if logging, there will be no data for the cranking period. If cranking when warm and thus long cranking, the connection seems to be lost for too long, and VCDS will throw an error message and disconnect - falling back to the menu.

Is it normal for VCDS to lose connection to the 01 engine during cranking? If not - could - say, a rapid negative spike-like voltage drop cause the ECM to shut down or do a cold/hard reboot? And If this were to happen - is it possible for something like this to happen without storing a terminal 30 low voltage code or similar (or any code at all)?

I'm not sure wether or not my battery is in good health (but it starts fine when cold) - the digital readout on my multimeter updates too slow to show a very rapid voltage spike up/down - and it doesn't have min/max reading. I've replaced a faulty CTS with a bench-tested and confirmed "good", OE unit. The fuel pump does get ~11.5V during cranking - but then again, a bit slow readout. I'm not in a position to blindly throw parts at it.

tofast2belast

you loose connectivity because during a crank start, the voltage to accessory items(I.E. 12v outlet, OBDII port.. etc) is reduced or momentarily shutdown because the cranking amps needed to turn the motor is so high that anything drawing amperage would otherwise make a less effective start procedure.

you can wire the obd to be 'always' on to test you logging.

pr0xZen

Do you happen to know if its live or ground switched? Is it a matter of pulling a direct battery +12v feed to pin 16?