Folks,
I thought The Duchess had forgiven me for failing to polish her every week but it appears this isn't so. Sometimes at the first start of the day she'll start straight up and stall out immediately. If I crank again there's a 50% chance she'll start and run fine for the rest of the day no matter how many times I stop/start.
If she doesn't start on the second hit, she'll crank for ever but never start.
Seeing as she has already had Plugs, HT Leads and Coils to fix the misfire (100% sorted btw) I'm guessing this is likely to be fuel. I think I've found the fuel test valve, and I have a fuel pressure test gauge thingy. I'm reading 50PSI as the correct fuel pressure for these beasts - but is there a spec for leakdown time?
Cheers,
Morat

When you go to start it, do you hit it straight away? I know with mine I’m in the habit of turning on the key and giving it a second or two to build pressure prior to hitting the starter. I have no idea if it makes a difference, just a habit.

Of course that doesn’t speak to your complete no start issue.

Having a good look at the fuel pressure might give you a clue. The pump runs for about 3 seconds from ignition being switched on to prime the system, then it runs while cranking and obviously once the engine starts. If it is priming but then not running while cranking that would give the problem you have.

I've tried doing the "poor man's prime" by switching on, off, back on before starting (with a few seconds pause in the middle). This didn't work. The maddening thing is it seems to go from Start -> No Fuel -> Stall to Flooded in two/three cranks. If you leave it 20-30 minutes after it fails to start it'll start up first time on the button.

I did try to watch the fuel pump state in the Nanocom under Motronic but it just showed OFF (or not running, or whatever it is) all through a perfect start sequence, which seemed a bit odd. I guess it doesn't refresh in real time.

What's the coolant temperature showing in Nanocom (on the Motronic ECU, not BECM/Dash)?

Mine was giving me hassles occasionally, and found the coolant temp sensor was reading -39.5 C when cold, and then starting to read a bit more normally once warmed up. Though as it was getting more intermittent, it sometimes wouldn't read right when hot either.

That was causing me to not be able to restart without troubles, and really weird gearbox shifting sometimes. Worth checking that out.

Ooh, good call. Sadly not this time though. I've just been out and the coolant temp was showing 19.5 degrees which seems pretty likely. Air temp was showing 21.5.
She started 3rd time on the key, having failed to start this morning. After running for 5 minutes, she restarted instantly.

This morning, instead of waiting 20 minutes I took the Jeep. I'm sure that had I got her running this morning she'd have started fine this evening.

There was a code this time. Upstream O2 invalid, occurred once. I haven't checked the codes since the coils were changed a couple of weeks ago so I'll see if it comes back.

That wouldn't affect starting unless the fuel trims had been steered way out, in which case it would still be the same after it had been started.

yeah, I think it's a red herring too.

Hmm. It had a new Bosch MAF in my ownership so, I'll get the fuel pressure gauge out tomorrow and see what it's at before a cold start. Clearly it's OK for the Running -> LPG phase, and it seems to be OK for the prime -> crank phase or it wouldn't fire up for that 1 second window before it dies. I wonder if it's possible for the fuel pump to cut during cranking?

That's what I was thinking. You'll have residual pressure in the fuel rail but if the pump isn't firing up then as soon as that pressure has gone, you'll have no fuel there to keep it running.

I wonder if you're being a bit quick on the key - turning it on, but then letting it turn back... I have noticed with my Defender 4.0 (which I use as my bell weather as I've had it almost from 5 yrs old, it has always been properly serviced and has almost undetectable HC in emissions testing) that if I am a bit quick to release the key ie before the engine's caught then I also have issue on the second turn - assuming same as you, over-fueling.

On the RR 4.6, it is generally well behaved, but in this weather it has missed the odd first-turn - and I haven't yet eliminated that being my poor key-turning etiquette (ie being too accustomed to the instant catch, but being too impatient to wait an extra couple of secs). It hasn't stressed me enough to get the nano out and start looking at temps yet, but I may do out of idle curiosity. I was looking at trims the other day though, and noticed the ECM uses the same 38.75% at start up that it was using in the winter, before the o2 sensors kick in - now, if I can only work out how the ECM determines that start-up value I could maybe fool it. Has anyone decoded the mysteries of the GEMS fuelling tables ? It had a new ECT last year, I can check it, but I doubt it's that.
On the RR, my IAT has an extra resistor across it which gives me an extra 10-15 degree boost, but typically still a few degrees below ambient. I did even have the IAT disconnected for a while (by accident) and although connecting it again it seemed to make starting a bit better, it was not dramatic. Which is all to confirm that the IAT prob doesn't have too much influence, as Rave implies

this all sounds a little familiar except its a bosch not a gems . fuel pressure is good at 50psi . the maf sensor controls your injection rate and the only fault i got was an o2 sensor high reading. you may have to make a lead to pin test the maf . good luck with it .

Roman - I'm not sure about the key thing. I just release it when I hear it fire - maybe I'll hold it longer next time and hope to avoid the horrible "too much starter" noise.

Mad-as I've been reading your thread closely but I'm hoping my MAF is OK as it's a new Bosch unit I fitted in 2017. I guess it wouldn't be the end of the world as they're still available for the Thor but I would be disappointed in the longevity of a £100 part if it has died :/

Having said this - it started perfectly for SWMBO this morning.