It had about 18 hours on a 4a smart charger but no the smart charger didn't show it as fully charged but I decided it'd be close enough, I've not got several days to wait for it to finally finish the last little bit 

So a new battery made zero difference, now I need to pull some ideas together of possible causes.

1st step I'm going to inspect the bcm and it's connector as there a known weak point. 

Second is to monitor live data at startup mainly fuel pump and rail pressure to ensure it's not something like fuel draining back overnight. 

Third the glow plug system, I assume it's a conventional setup of a timed relay controlled by the coolant temp sensor? I'd expect a fault code for something glow plug related but it should be simple enough to confirm correct operation.

Lets see where those ideas lead us, 

Thanks

Chris

Agree with your other ideas.

I am very interested in what you find on the glow plug module.

Whilst it used to be one relay activating all the plugs, I believe it is now individual MOSFETS activated by the PCM allowing feedback on any faults. Our Nagares aluminium finned thingy with 8 connection!

My problem is slightly poor first start from cold with no glow plug light above about 6 degrees external temperature (not yet determined)

I don't know if any activation is happening BUT Forscan has some parameters but obviously needs one person to watch and start and someone else to monitor.

My next step would be to test current flow with a clamp meter (all glow plugs showing 0.5 Ohm resistance i.e. look sound)

Not had time to look at this any further but the last couple of days the temperature has been around 10 degrees on a morning and what's happening is, press power button ignition turns on, press power button again it starts so it's definitely better when not having to wait for the engine to complete full preheat.

I'd be inclined to think it's related to the pre heating, but the car should try to start when I first press the button, I shouldn't have to press it twice 

So this morning following the school run I decided to fold myself into the passenger footwell to look at the bcm connector that's famed for corrosion. 

There's a small build up around pin 9, I don't think there's enough to say it's an issue, as I inspected without removing the glovebox I can't get a good look at the corresponding pin but given there's something on the plug I'll whip the glovebox out at some point and give all the plugs and pins a good squirt of electrical cleaner. 

My instinct at the minute is sitting with the glow plug system, At some point I think I'll remove the actual glow plugs and test them, I've no idea if there the originals on 146k or if they've been changed, they are a consumable so an inspection is probably worth it. 

Thanks

Chris.

So if anyone's still following this I think I've found the issue, sort of. 

The issue appears to be a ground issue, before delving any further and starting to dismantle anything I decided that today before work I'd run an extra earth between the engine and the battery, basically I've attached a jump lead to the battery negative and the engine lifting hook and the cars fired up straight away this morning. 

I may go around the earth's and clean them all at some point or I may just buy a pre made earth lead and add a permenant extra earth lead, some issues aren't worth chasing when there's a reliable work around.

Chris. 

3 hours ago, thomp1983 said:

I've attached a jump lead to the battery negative and the engine lifting hook

Won't that have bypassed the BMS?

I wouldn't of thought so, I can't say for definite as I've not looked but the average ground system on a car goes, negative post to chassis then either negative post to engine/gearbox or engine/gearbox to chassis which in turn returns to the negative essentially it's all supposed to be a big loop. 

If somehow I have bypassed the bms I'm sure a fault code will show up somewhere but I'll keep an eye out. 

On cars with BMS the sensor fitted to the battery negative post is in series with the earth cable so current into and out of the battery is monitored. Connecting the jump lead in the way you stated will effectively short-circuit the BMS sensor.

Having owned a Mk3 I can confirm that there is only a cable from the BMS to the chassis earth point on the nearside suspension tower. The engine is earthed to the chassis at a different point.

And by the way the correct grammar is "I wouldn't HAVE thought so".

I see what your saying, the jump lead was just a quick and easy way of providing an extra ground to the engine to see if it had an effect on the starting issue, if I add a new ground lead all I need to do is add it after the bms sensor which is easy enough. 

There is a possibility that if I put the ground lead after the bms sensor the issue may return but it's helped narrow the issue down.

Indeed. I think I remember reading on here that connections to the body earth points were commonly made without the paint being cleaned off, relying on the nut cleaning the stud threads, so you may well find the suspension tower connection is the culprit.

If you can move your jump lead to the BMS terminal that would be a good test.

So this problem is still there, while I was swapping the gearbox I removed and cleaned all the earth leads and rubbed the connection points back to bare metal.

I also cleaned the mounting points for the cables to the starter motor where they connect to the main fuses in front of the battery. 

I also took the opportunity to replace the glow plugs, the car now starts consistently on the third press of the button this is leading me to it being glow plug related but I'm at a loss to understand what can be causing it. 

Chris. 

Look here for my thoughts today on glow plug module testing and Forscan PIDs which may, or not, be relevant.
Module should trigger straight away if cold conditions (coolant temp etc) exist?