X5 3.0d won't start

[omodos]

Originally Posted by andrewwynn

Thanks and that would be awesome to have a diesel example. I've been wanting to get this concept of there ever since I read about the exponential growth of current draw as a starter wears out. Since many of not most DIY car fixers have a DMM and with the X5 having two separate paths for electric flow from the battery it makes this trick possible.

The cig socket gets its power from the feed that comes up the right side of the car, the starter gets the power from the big cable that goes up the left side past the B+ jumper and the alternator.

I'm not sure what power is cut off during the start but it's possible the value can be thrown off if something like the fan or wipers was drawing power up the right side. That said this technique should work very well to get a read on the starter current. I don't think the diesel or V8 has a thicker starter cable (which would change the 285 factor)

@Andrewwynn and wpoll, I think I have hijacked this initial post so apologies, please see the crude diagram tell me if I am on right lines...dv will be set to 12v dc of course
PS on my diesel the starter is pretty much behind the alternator and not sure the B+ feeds straight to alternator(generator as it is called here) or the starter

[wpoll]

On the diesel, it looks like the B+ runs right to the starter first, then hops over to the alternator...



https://www.newtis.info/tisv2/a/en/e...erface/hORvXOt

[omodos]

@wpoll, so we can still use andrewwynns trick to test the starter draw via the dc lighter and B+?

[andrewwynn]

As long as the feed for the cig lighter takes a different path it will work. The "285" ratio will be different if the length of cable from battery to tap is a different length, that said. This trick measures the voltage drop from battery to the to the firewall not all the way to the starter so if the diesel has the starter on the left it shouldn't make much difference.

[omodos]

Thanks sir

[wpoll]

Originally Posted by omodos

@wpoll, so we can still use andrewwynns trick to test the starter draw via the dc lighter and B+?

Yep, as Andrew said - it'll still be close and work fine.

The circuit diagrams are a bit variable on the main B+ lead from the trunk (boot) to the firewall/starter/alternator - one diagram shows the cable as being 70mm sq. and another shows it as being 95mm sq.

That's a BIG cable!

[omodos]

Ok Wpoll appreciate yet again response, so basically should see a voltage drop on digital voltmeter from 12v or whatever battery will be reading down to 0.whatever on startup...hope nothing fries

[andrewwynn]

You will see almost no voltage until you start to crank. If you see voltage like 0.1v wait until it drops, turn off any power draw like fan. You might see a negative value which will happen when power is coming up the right side cable.

70mm SQ is about 9mm diameter

[omodos]

Thanks andrewwynn shows how much i know....will give it try on sat

[wpoll]

Originally Posted by andrewwynn

...70mm SQ is about 9mm diameter

Yep - I wasn't thinking that 70mm was the dia. - but even so, in a vehicle, that's a decent cable!