BMW M4 f82 F80 crank no start

[Ttgrease1]

Hello, I purchased an M4 damaged with airbags blown, replaced airbags, rads, Engine oil & filter. Started on the first try with help of a jumper pack, ran beautifully no leaks etc.

I left it for a few days now it cranks strongly but doesn't start, I can't hear the fuel pump priming in the rear when I unlock the car also the battery isn't the greatest & I haven't installed the new BST(I've just joined the old blown BST together).

Hooked up my scan tool & the codes I'm getting on the engine are: 164020 Intake camshaft sensor, electric: Short circuit to B+.

My guess is either the battery needs replacing, funnily enough it's a Lead acid battery & not even the Lith ion one OR there's no fuel coming up.

I must add, on the positive terminal the two pin airbag wire was disconnected & negative IBS sensor was too, well the lead acid didn't have a built in ibs.

My theory is: the DME isn't authorising the fuel pump to function because the car thinks it's been totalled OR can low battery voltage cause the DME to not authorise the car to start.

The real question is, how comes it started the first few times with help of the jump pack