Brilliant - thanks very much - I didn't know you could just buy the seals for the regulator, I'll certainly look into that. I'll post the rail pressures shortly. :)

Typically, she is starting fine now :dunno: as the misses has just done some odd trips and not an issue starting at all - starts everytime on the first rotation .. :swear:


Ignition On


- Pre-supply pressure is 3.8 Bar

- Rail Pressure is 0.0 Bar
- Regulating Value is 0%



Engine Started


- Rail Pressure is 360 Bar when starting, then drops to 307 Bar for a few seconds, then drops to 296 Bar where it stays on idle.

- Regulating value is at 18% when idle


I'll try again when it will not start to see if I get different readings.


Thanks for everyones help thus far .. :thumbup:

Those pressure figures look very normal. If rail pressure is that high while cranking it unfortunately rules out pressure regulator seals as the cause.

When the problem occurs I would also try to unplug the rail pressure sensor if it's temporarily giving too low figures because of internal failure or just because of poor contact on connector pins.

I will do that thanks - I read the TIS on fault finding yesterday and it says the same thing - simply remove it and if it then starts, it must be the sensor. I knew you could do that with the MAF, but didn't think it applied to the fuel pressure sensor too.


I'll post the results - could be useful for the E53 3.0d community to quickly identify if the sensor is the problem or not.. :D

I would probably renew those sensor connector pins anyway as a preventative measure because they are known to cause other running problems when the internal contact splices age.

Part nr. 12512247474

https://static.schmiedmann.dk/Produc...314504_big.jpg

Wow - you really are a world of E53 knowledge - thanks so much for this info - It's very much appreciated !

So some good news - I think. The car hasn't been driven much but today she didn't start when cold and on the drive, so an ideal opportunity to test the above theory and remove the Fuel pressure sensor connection and see if she'll start. This I did (just unplugged it) and she fired straight away .. :) I turned off, put the connector back and again she fired fine. So I'm going to get new connectors to see if that resolves it once and for all, failing that a new fuel pressure sensor - but at least I'm confident now that I'm looking in the right area. Thanks to all - almost there.

Spoke too soon .. .. so just spent the last 2 hrs removing the intake manifold (again ..), finding the suspect ground wire on the fuel pressure sensor, cutting it out and soldering in a new wire, all heatshrinked. All put back, fires first time great - 15 mins later on a hot engine - no start again ... :banghead:

Checked the 5v reference, ground and signal so know wiring is now good.

It's got to be the sensor itself - so have just bought a genuine Bosch one with the new insert and washer.

I'll do a DIY when it arrives as I know how to get the intake manifold off with my eyes closed now ..:rofl:

So thought I'd post an update.

Since the last post I've received the fuel pressure sensor but the car hasn't had any non-start problems .. until today :rolleyes:

As usual, a sniff of brake cleaner was all that was needed to fire her up.

So this morning I replaced the fuel pressure sensor with a new Bosch RDS4 sensor (the old one was an RDS2) - and while the inlet manifold was off I replaced all the glow plugs as well. (very hot engine and plenty of pen fluid and they came out without bother). All were open circuit/dead. My E53 has the relay controlled glow plugs (not solid state) and after testing the 'controller' and cleaning the relay contacts all was well. The error code for those has now also cleared - zero faults on the DME ! Hoorar ..

While in there, I also replaced all the vacuum lines as the rubber had perished on the majority of them, they crumbled when I tried to remove from the vacuum manifold so a well overdue replacement. The turbo definitely spins up faster, so I am glad I did this.

I don't really fancy the HP fuel pump or regulator .. so fingers crossed this is the last gremlin.:thumbup:

:banghead:

I'm really starting to lose patience with the X5 now - hot starts are at least consistently bad now :bustingup

So after the new HP pressure sensor and glow plugs, zero difference to hot starts.

Leave it for 30 mins, come back and she fires just fine or a sniff of brake cleaner and she fires just fine.

Under no start conditions fuel pressures as follows :-

LP - 3.59-3.60 Bar
HP - 276.36 Bar (while cranking)

I have noticed the HP fuel pressure drop very quickly when stopped (at 1 second intervals) - 276, 225, 153,31,20,20,20,10,10,10,10 - so within 11 seconds it is down to zero again ?

On a 2nd crank, it's back up to 276 again instantly.

Compared to an instant start (cold or only warm engine) -

LP - 3.9 Bar
HP - 296 Bar (Idle)

So can I rule out LP and HP fuel pressure ?