thanks wpoll, any feedback is much appreciated, temps out here hit 6c maybe about 1 week a year.....and feels like hell to us used to 30c plus nearly all year round! don't sweat if you can't record it and have to wait for better weather....right so I will be eliminating a bad(ish)engine to earth IF I get more of a healthy start with the jump leads from -ve to engine applied. I will post results if any.

On that 392 Amp reading ...

yes, the negative does not matter.

But, do you have more info on what the current was initially, vs. what it was while cranking? Typically there should be an intial spike as the engine starts to spin, followed by a reduced reading while it is cranking steadily.

DC motors, like your starter, will have a "back EMF" which reduces the effective voltage driving the motor. Basic physics, Lenz's Law, which cannot be circumvented even by BMW. BTW, that's why electric cars tend to have such phenomenal initial acceleration (low speed, little back EMF, full effective voltage to the windings, max torque), and then taper off as the motor is spinning at higher speed (high RPM, bigger back EMF, reduced effective voltage to drive the current through the windings, reduced torque).

Here's a very accurate article I found describing this in more detail for automotive starter applications:
Starter Motors and Circuits (Automobile)

So, thinking on this a little, if your battery is putting out 392A, that seems like the battery is working pretty well. Dropping to 9.5V while cranking does not seem unreasonable. Battery is putting out almost 4 kW - should be plenty ; it's doing its job. And BTW, when you take measurements like that, the exact location of the measurement is important. E.g, at the battery posts, vs. at the jump ports, vs. at the starter. With so much current flowing, even with low gauge wiring, you'll lose a half Volt or so across the wire. No doubt the battery is not perfect, and jumpering in a booster battery should make things better - but I would not think that means your battery is at fault here.

So if 392A is flowing through your starter, somehow it is not turning those Amps into torque. And because it's not getting the required torque, the engine does not spin quickly, and the back EMF stays low, and the current stays high ... while still failing to spin the engine.

I think this points to a problem with the starter, or with the wiring/connections, probably near/at the starter.

In my experience with only a very few failed starters over the years, they seem to fail following other engine problems that caused hard starting. This meant that the starter would be over-worked, and over-heated, which would eventually cause the starter to fail. Have you had any problems like that over the last year or so, where the engine would spin fine but fail to start due to an engine issue?

This may be a case where you might get more info by doing repeated tests, monitoring current and voltage at the battery, with the DME relay removed so the engine does not start. By doing it repeatedly, you will probably end up heating up the failed component (probably in or near the starter), which might result in measurements to better isolate it.

Unfortunately, the starter is not an easy thing to get to, and even harder to replace, and that should factor in to any decisions. Here's a pic of my starter (the cables with red on them are seen going to the solenoid which is attached to the starter assembly there) in my 3.0i with the intake manifold and cylinder head removed. I'll say that even with that apparently easy access, it was not as easy as it looks to remove and rebuild it - which was done just because I was in there. Had no problems before or after.

Attachment 74697

Attachment 74698

Thanks for the in depth explanation greatly appreciated. the amp draw at startup peaks at 392 and other time went over400 but then when running i think had a reading ok 20amps...need to find video from test....not had any other failures...oem battery that lasted 10 years replaced 5 years ago with a bosch one...spoke to my mechanic again who told me new battety and starter and i wilk see a difference. Just curious is there no access from under the car to remove the darn thing?. Im.still a stubborn git want try chassis to engine bay ground to eliminate this as issue but cant see anywhere i can hook up jump lead on engine...is oil filter housing ok.?

BMW E53 X5 3.0D statup recordings
 

OK, here's the requested recording. The video recording was made inside the car but I recorded the audio from outside the car and edited the two media tracks to create this clip. The first start up is with the exterior sound, then the repeated section is with the interior sound: -



https://youtu.be/YTCJstGcayU

Fella owe you one for taking the time to do this...100% sure your start is better...i will record mine too amd compare...again thanks

I don't know whether to be sad that yours is not as good as it should be or very glad that mine seems OK! ;)

No worries...nutty thing mines been as it is now since day 1...only times it has got better and much much quicker , faster than yours was on near no start conditions where i had key in on positiob for a good 20 seconds or so...then turning to off and back on it just jumped to life i could hear the starter spin much much faster...anyhow at every mot inspection guy always tells me battery on weak side...so i either go for a new battery see how things go, or go for the starter too as having a shot starter will eventually do bad for my battery. In law has a diesel crv...shoots into life when you crank the key...even faster than yours but lets not go there and compare apples with oranges eh? Again much appreciated.

Mine is much quicker when the outside temp is higher than 6.5DegC. !! ;)

Good point...

Morning,Wpoll for the life of me cannot find a place on the engine to hook up the jump cable from to the chassis or -ve jump point bolt, can i go from the oil filter housing if the clamp can fix there to the -ve bolt in the engine bay? you can still see i am obsessed with bad ground engine to chassis yes?


PS never started at all today...5 mins n ctek and was enough juice to start it (laboured as usual) very tempted to go for new battery and agm for that matter and take it from there