Suddenly MES stops logging after a couple of seconds

[Modano]

Hi,
I'm using MES to debug my non starting 156 2.4 jtdm.
I wanted to check some signals (EGR signal, FUel pressure and obviously RPM)
When idle the monitor is fine.
When I try to start, after 2 seconds the log stops totally (my RPM is still at 250 rpm). I know the voltage of my battery is severely dropping of course, but may this explain the cut ?
I also tried to start and to MES with a running car battery aside, the cut still occurs very early in the start process, unable to graph or monitor any value (and the car is not starting of course )
I rebooted my machine and everything was fine with MES until now, no change in cable or settings.

Thanks !!

[Modano]

I tried a not so fresh battery (4 yo) and voltage drops at 10 V while (not) starting, .... but MES drops as well as with the previous battery.
Will buy a new one, but I'm not that sure it comes from a low voltage...

[Modano]

I managed, after 3 or 4 battery charge and 10 minutes of trying to start it.
WHen started it runs very smoothly, no problems whatsoever....and MES is running fine when engine is up....
At least the ECU isnt gone

[Modano]

Even with a new battery......
The voltage is considerably lower than the Battery.
When it stops, it drops to 8V... with a brand new battery (even exhausted by my troubleshootings).
Would this be an expected behaviour ?

[shpuncik]

you get 8V on car battery measured with digital meter or on MES screen? what do you mean by "voltage is considerably lower than the battery"?

[Modano]

Voltage, seen by MES at the ECU was ranging from 12.5 to 13.4V when engine as idle (changing every half second or so).
When measures at the battery, it is 14-14.2 steady.


But today I made a cleanup of all positive power supplies (ECU relay, Fuel pump Relay, ECU Fuse) and I got a rather steady and higher voltage (13.6 to 13.9) !
I could start my car while MES was plugged in, but the car started right away so don't know if my topic is still valid or not.
Will do a couple of tries (anyway I'm in lockdown )