Crikey give it a rest. First of all, that cranking screenshot was taken last night after i had deliberately tried to lower the battery voltage to provoke the non start issue and was the fourth stop/start crank in a row.

The gadget is good enough to monitor slow battery drains over days and weeks, car waking up intermittently and show your charging characteristics and more importantly share the data with other people in the world for help and advice. If you read my other Thread , this may actually turn out to be normal behavior because someone else with the same gadget has the same behavior - so we either have the same fault or NO fault.

Feel free to post the data from your £2k lab grade scope collected over weeks of journeys to help move the understanding forwards.

Do you really want me to setup my digital scope triggered on ch2 on the starter trigger to see how that compares with the £25 gadget?

Phoenix wrote:

mezo wrote:

... from a cheap datalogging device and is handy to see what’s going on and keeps a history in order to try and determine any patterns or eliminate areas - it’s not a precision instrument, but it’s not bad.

...
.

I don't agree, unless the voltage being measured is shown with some sort of verifiable, repeatable accuracy, it could well be sending you off on a wild goose chase, there is also the issue of confirmation bias - 'it's always that cause, so it must be that cause in this case' type of thinking, also, I'd take issue with an indicated 9.85VDC during cranking being 'OK', it most certainly isn't, anything below 10.5VDC during cranking is an issue, on any 12V vehicle.

It would be better in my view to measure volt drop end-to-end during cranking to determine if the issue is the circuit or the supply to it.

yes you might be right. Mine wouldn't start yesterday, i was probing around in the relay box to trace the wiring and fuses etc - when i plugged the connectors and relay back in - it started again. I replaced the wire anyway, but it could indeed be between the live feed into the fuse box, the fuse, relay base and the connector.
I didn't manage to capture any readings - but i know exactly where to look now.

mezo wrote:

Crikey give it a rest. First of all, that cranking screenshot was taken last night after i had deliberately tried to lower the battery voltage to provoke the non start issue and was the fourth stop/start crank in a row.

...

Feel free to post the data from your £2k lab grade scope collected over weeks of journeys to help move the understanding forwards.
...

mod edit..

please keep posts civil.. ... - .- -.




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ffrr14 wrote:

All that said there is a design/dimensioning issue somewhere.

Quote:

I'm familiar with the engine in question, in my view, due to the high inrush current required, I would have sized the cable at 6mm2 and given it a dedicated fused supply to the relay, or ideally twin 70A relays, again, due to the high inrush causing contact arcing. Its possible that the issue may be caused by the starter solenoid piston, fork or drive dog binding which will keep the primary 'pull-in' windings active for longer than design time before the 'hold-in' windings take over, thereby causing heating of the conductor and increase in resistance with the resulting drop in terminal voltage.
But all that is just a guess.

I think you have to work on the SoC will be ~75% for any calculations, I've not measured the cold inrush current but it's safe to assume it'll be in the 30-50A range, probably dropping to ~27A once the field is established with a further drop to 12-15A once the starter is fully engaged and spinning - which brings it's own challenges with system voltages, are you getting any transient lost comms ('U' codes) DTC's? if not, then the overall vehicle voltages are remaining at healthy (>10.5VDC) levels and the issue is purely within the engine bay distribution and harness'.
Personally, I'm not keen on the pressed & folded type of primary distribution used in LR (and others) fuse & relay modules, i'm sure they are capable of providing the required current in each circuit, the problem I've found is that when there are multiple circuits claiming current from the same single incomer, particularly in a 'jump in & go' scenario, issues arise with ageing copper.

No DTC unless I am working on the car etc. Your thinking resonates, I have replaced all the relays and now separated the solenoid load from the engine distribution box.

I will go back to the distribution behind battery and replace with 13mm flange niloc nuts at some point, I feel this is also a weekness in the system.

I am also looking for earthing points on the chassis and refurbush SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

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If you have access to one, use a high sample rate datalogger or multimeter with min/max recording to measure the PD between the -ve terminal and the engine, move the body measurement point closer to the starter with each test, if there is any detrimental resistive connection or lead, that'll find it.

Don't do the tests too close together time-wise as the current flow paths will be heated (and resistance increased) with each use. This is one of the pitfalls often missed.

Ffrr14 - having literally just been in the battery bay junction boxes this eve cleaning all the contacts, I’m curious as to the nylon flange nuts suggestion. Genuine Q, what’s the advantage of those? Why do you think the standard nuts are a weakness of the system? Every day’s a learning day for me on here. TYIA! Andy

2010 4.4TDV8 Vogue SE in Santorini Black with Ivory interior
2017 Audi SQ5 3.0 V6T Quattro in Volcano Red
2001 Audi Allroad 2.5 TDI manual with low-range in Highland Green. Currently SORN whilst undergoing some serious restoration!

Phoenix wrote:

If you have access to one, use a high sample rate datalogger or multimeter with min/max recording to measure the PD between the -ve terminal and the engine, move the body measurement point closer to the starter with each test, if there is any detrimental resistive connection or lead, that'll find it.

Don't do the tests too close together time-wise as the current flow paths will be heated (and resistance increased) with each use. This is one of the pitfalls often missed.

Ajmngn wrote:

Ffrr14 - having literally just been in the battery bay junction boxes this eve cleaning all the contacts, I’m curious as to the nylon flange nuts suggestion. Genuine Q, what’s the advantage of those? Why do you think the standard nuts are a weakness of the system? Every day’s a learning day for me on here. TYIA!

I am hoping the Niloc nuts wont come loose vs the standard ones (I have found one loose, likely due to heat and vibration etc)

This is strictly my opinion only

Click image to enlarge

 SOLD | Tuned MY 2011.5 Range Rover Autobiography 4.4 TDV8 Orkney Grey | e-diff | ACC

New Toy: Unimog U1550L/37
New : G350D

Makes sense! TY 👍 Andy

2010 4.4TDV8 Vogue SE in Santorini Black with Ivory interior
2017 Audi SQ5 3.0 V6T Quattro in Volcano Red
2001 Audi Allroad 2.5 TDI manual with low-range in Highland Green. Currently SORN whilst undergoing some serious restoration!