Voltage drops below 9V when trying to start

[Mikester349]

Hi all, I have read mods post and any help given will be much appreciated and reciprocated.

For the last couple days I haven't been able to get my 2.0tdi A4 to start. OBD showed no fault codes but battery light is on when turning on the electrics. Noticed the battery was sitting at 12/12.6V idle but dropping right down to 8V when cranking. When hooked up to another vehicle for a jump start to goes up to 13.7V but still drops down to around 9V when attempting to start it just cranks and doesn't ignite. 

Got a replacement battery today but still have the same issues with a brand new battery. I was told this might be a DPF issue or a glow plug issue. What do you all think?

Also within the last couple months I've had the EGR replace and the timing belt and pump replaced too. Screenshot is from a couple days ago, still showing the exact same reading with the new battery.

[Mark M.]

I've seen batteries with a weak cell drop to under 9volts when cranking but if the new battery is ok then I'd wonder if the starter motor is faulty/jamming causing the power drain.

[Mikester349]

Thanks Mark, 

I'll have a look at that tomorrow, also forgot to check the fuses but the starter is turning so I doubt it's the fuse.

[Magnet]

Hello Mike,

Sorry hear of your issue. 
Before delving into more complex possibilities, have you checked the main earths - off the battery and across to the engine?

Good branded replacement battery fitted? 
Kind regards,

Gareth. 

[Mikester349]

Hi Gareth, where can I find this? Are you talking about the black wire that's coming from the ground terminal?

Yes, this new battery has more CCA than the last as well.

Today I'll be checking that, the fuse box, relays under the wheel and also the ECU relays, possible also crankshaft sensor if I can get under.

[Magnet]

Thanks Mike,

Yes, you need to check the heavy black wire running off the negative terminal of the battery. Also the probably unsheathed heavy flexible cable that connects from the chassis to the engine or gearbox. Disconnect the positive cable and if possible unbolt the earth cable off the chassis earth point and throughly clean the terminal and chassis, before reconnecting. 
Again with the battery disconnected, check and clean the terminals on the starter motor. 
Once you have done all that, reconnect the battery and test. 
Relays, crankshaft sensor checking?? This car is never going to start (even if cranking over) with an under-load voltage of <9 volts. 
Suspect may well be the starter solenoid/ starter, if no faults found. 
Battery quoted CCAs can often be rather like car manufacturers quote mpg figures - ‘embellished’! 
Brand of battery? 
Kind regards,

Gareth.