Starting problems

[AndyPagin]

Late 2005 W211 E320 CDI Estate
I bought this car about six months ago, for months everything was ok, then it wouldn't start.
All the usual lights on the dash but just a faint click on turning the key. After a few attempts it starts and runs fine.
I changed the battery for one I know to be good. Worked fine for a couple of weeks, then same problem again, even after fully recharging the battery.
The F59 (I think) fuse has been upgraded to 20Amp and has continuity, though I tried another fuse just in case.

Checked it with an Icarsoft MV 2.0 diagnostic tool...

Engine off:
Voltage (DLC) 12.28 - 12.41 Average 12.33

Engine on - No load:
Voltage (DLC) 8.46 - 12.41 Average 11.92 (same reading with a multi-meter on the jump start posts in the engine bay).
Revving engine doesn't change this.

Engine on - Headlights and Heater/Aircon on: Average 11.88

Can I assume the voltage regulator on the alternator is dying?

 

[DSM10000]

Late 2005 W211 E320 CDI Estate
I bought this car about six months ago, for months everything was ok, then it wouldn't start.
All the usual lights on the dash but just a faint click on turning the key. After a few attempts it starts and runs fine.
I changed the battery for one I know to be good. Worked fine for a couple of weeks, then same problem again, even after fully recharging the battery.
The F59 (I think) fuse has been upgraded to 20Amp and has continuity, though I tried another fuse just in case.

Checked it with an Icarsoft MV 2.0 diagnostic tool...

Engine off:
Voltage (DLC) 12.28 - 12.41 Average 12.33

Engine on - No load:
Voltage (DLC) 8.46 - 12.41 Average 11.92 (same reading with a multi-meter on the jump start posts in the engine bay).
Revving engine doesn't change this.

Engine on - Headlights and Heater/Aircon on: Average 11.88

Can I assume the voltage regulator on the alternator is dying?

Engine on, no load should see around 14.4 V

11.88V with the engine running is discharging the battery.

For an accurate reading only take the static and running voltages from the battery terminals otherwise you are including voltage drop due to the resistance of the wiring etc involved.

An Auto electrician or any Garage should be able to properly check the battery and charging system under electrical load.