e53 M57 3.0d 2006 intermittent starting

[AUSBMX]

Hi all,

Hopefully someone can lend some ideas here - I've done a lot of googling/code reading but getting stuck - essentially the car will intermittently crank but not start. It's my mums car, she's already had it at a diesel specialist for 2 months who just charged her $1700 and just changed the glow plugs and starter motor (I said they weren't the problem, but oh well, it does crank a lot faster now @ 250 RPM). Initially I suspected either injector leak rate too high, pressure reg on rail, or the flow control valve on back of HPFP (I'd already checked pre supply pressure looked okay @ 4 BAR +).

After changing the glow plugs and starter the mechanic decided the problem was the pressure regulator on the rail, he also said he couldn't find a new pressure regulator anywhere, and that the rail was damaged somehow where the regulator screws on (no idea how that could happen), so needs a new rail as well. I ended up going to the wreckers and pulling a rail + regulator off a e53 x5 there and sending it up (also took the flow control valve off the wreck as well just in case). Apparently this 'fixed' the problem, and my mum took the car home - it apparently broke down a few times on the way home, apparently losing power on the highway, but she managed to limp it home. It would start fine, but the throttle had zero effect on the engine, and CHECK FUEL INJ SYSTEM would come up on the dash. This problem then randomly disappeared, and she used it for like a week with no problems, then the problems started happening again as before it was sent to the mechanic. She managed to start it the other day, and just immediately drove it to me in Melbourne (3~ hours away), and borrowed my spare car to get home. After she parked it, it wouldn't start, just crank.


Original symptoms: Occasional starting problems, both hot and cold, but more common hot. Usually can just try again in 10 seconds and it will start fine and drive fine with typical power level. Sometimes multiple hours wait before it will start, however always once started there is no problem, even under high load (100% throttle). Occasional problem started ~12 months ago, but was very rare (ie once every few months), however has got increasingly common, now every day.

Battery is near new, fuel filter was replaced ~12 months ago.

I've got ISTA+, so I've looked at all the fault codes and taken a few videos monitoring Rail Pressure for successful starts, and unsuccessful starts.

This is the faults that come up after initially clearing all faults, and starting successfully and taking for ~5 min drive (including some 100% throttle).https://drive.google.com/file/d/1rrI...ew?usp=sharing

1A IHKA: Relay, heated rear window (think this is just a bad relay in cargo area)
BD IKE: Electronic braking-force distribution (No idea what's causing this, but some googling suggests its common and may be a bug)
4212 DDE: Glow plug, cylinder 1 (these were just replaced recently, but I don't believe in these temperatures (Melbourne Australia) we ever really need glow plugs).
54C6 VTG: Oil Wear (Probably legit but unrelated to the actual problem, I've got a bottle here to put in when I get around to it).

A video of the start+short drive of while monitoring fuel rail pressure in ISTA+ shows basically as you would expect: https://drive.google.com/file/d/1VIH...ew?usp=sharing

Can achieve ~1600 BAR rail pressure no worries.

Now after driving, parking, and turning off engine, I crank and fail to start 3 times:
https://drive.google.com/file/d/1z19...ew?usp=sharing

Oddly the rail pressure doesn't budge off of the pre supply of ~4.3 BAR all 3 times even while cranking at ~250 RPM. Another oddity is before cranking the rail pressure seems to digitally jump between 2.1 and 4.3 BAR occasionally. Is this just poor pressure resolution at this low pressure? Maybe dodgy pressure sensor/wiring/DME? Although I believe there is some logic that would flag a faulty pressure sensor and throw an appropriate code.

To rule out any battery issues, I also monitored battery voltage while failing to start: https://drive.google.com/file/d/1Mti...ew?usp=sharing
Initially voltage before crank: 12.7V, and drops to 11.2V while cranking at 250 RPM, which seems pretty good to me, back to 12.4/12.5 after finished cranking. Note I've got a trickle charger on the whole time while I'm messing around with this.

I have noticed in the past a bunch of error codes like "IKE: No CAN identification (DME)", "IKE: EGS signal line disturbed", and "No message, receiver EGS, transmitter DME-DDE" - but I think these are likely just due to messing around trying to start without a battery charger for extended periods of time and probably just due to low battery voltage.

I've checked all the fuses in the glovebox and electrical box under the bonnet, all good there. Perhaps an intermittent relay... I can clearly here the fuel pump relay clicking in the glovebox when I use the Prime function on/off in ISTA+, but I haven't investigated any relays further.

So after failing to start a number of times, these are the error codes I get:
https://drive.google.com/file/d/1yyI...ew?usp=sharing
S0017 No communication possible with: Multifunction steering wheel (However the volume controls still work and cruise control controls?)
1A IHKA: Relay, heated rear window (Same as before)
BD IKE: Electronic braking-force distribution (Same as before)
S0046 No communication possible with: Telephone
4212 DDE: Flow plug, cylinder 1 (same as before)
4B90 DDE: Rail-pressure monitoring on engine start (makes sense...)
54C6 VTG: Oil wear (same as before)

It should be noted this failing to move from 4.3 BAR while cranking seems to be new, when I've looked at this in the past it would rise up to ~70 BAR and then fall again while still cranking, but I didn't manage to record the screen. Here is an older recording before the replaced starter motor: https://drive.google.com/file/d/1Bb3...ew?usp=sharing


I just went out to try to reproduce the problem but it started fine like 20 times in a row, at one point the car stoped cranking entirely though, ie when you turn the key to make it crank, nothing happens - no relay click or anything. Repeated turning fully off, and trying again didn't do anything, even removing key entirely and reinserting, finally I removed key, locked and unlocked doors and then it worked and started as normal. Also no extra error codes appeared after this - might just be some internal protection due to trying repeated start/stop events while I was trying to get it to fail to start.

Other things I've checked are a smooth running test, and all injector values are easily in the acceptable range, so don't think it could be crazy injector leak off.

Any ideas where to look? Sorry for the wall of text, hopefully it makes sense!

Edit: Forgot to mention, currently ~ 3/4 full of diesel at the moment.