Before i just give up can anyone help - poor starting D5

[GrahamBrown1]

What is the rail pressure when cranking, it needs at least 250 to 300 bar to even run. This is where I would start. If you have low rail pressure then you either have a drain on the system such as leaking back to tank/pump or a lack of supply, ie weak HP fuel pump ect.

[Thassos]

what sort of miles has it done, and whats the service history looking like?

[Ga73]

Thanks guys,

The car has done just under 148k.. Not sure on the service history as there was none when I bought it a good few months back.

I've added a non return valve to the fuel line so I don't think I have fuel leaking back to the rack but does the HP fuel pump have a non return built in?

Agreed it seems a lack of pressure that's stopping it starting but can't understand why this happens more when the engine is up to temp

[Baffler]

Originally Posted by Ga73

Agreed it seems a lack of pressure that's stopping it starting but can't understand why this happens more when the engine is up to temp

If this were a petrol variant with these symptoms I would be looking to the Fuel Pressure Regulator...behaves fine on a cold start then plays up when up to temp 🤔

[Gotcha]

So I had a similar issue on another car I owned. It will only do this when the engine was warm.

I replaced the knock sensor and all was well again.

When it was warm and didn't want to start, I poured water over the sensor to cool it, and the car started right up....maybe give it a try.

[GrahamBrown1]

Originally Posted by Ga73

Thanks guys,

The car has done just under 148k.. Not sure on the service history as there was none when I bought it a good few months back.

I've added a non return valve to the fuel line so I don't think I have fuel leaking back to the rack but does the HP fuel pump have a non return built in?

Agreed it seems a lack of pressure that's stopping it starting but can't understand why this happens more when the engine is up to temp

The common rail system has diesel return built in, from rail to hP pump rail to tank and injector leak off. Heat can affect components in strange ways. You need to see live data on what is happening to the rail pressure. If it’s isn’t low you have a different fault obviously but if it’s not high enough for diesel to atomise it will never run. The ECM controls pressure via pump regulator. Have you checked this?

[Ga73]

Hi Graham

When you mention the pump regulator, are you talking about the pressure control valve?

I've replaced this with a used one if that's the case.

The car does run but it's more of a case of when it's hot.. For example if u go into a shop then return a few minutes later chances are it won't start.. If I go somewhere and return an hour later it'll start up without much fuss.

[GrahamBrown1]

Originally Posted by Ga73

Hi Graham

When you mention the pump regulator, are you talking about the pressure control valve?

I've replaced this with a used one if that's the case.

The car does run but it's more of a case of when it's hot.. For example if u go into a shop then return a few minutes later chances are it won't start.. If I go somewhere and return an hour later it'll start up without much fuss.

Yes fastens to side of the pump with 2/3 bolts.

Sounds like the only thing you haven’t changed is the High pressure pump.

[Thassos]

Another long shot, would an EGR valve stuck open or sticking when hot cause problems starting? Just a thought...Although i suspect yould get some error codes, as i know on the earlier Eur4 engine the egr has a sensor that feeds back the position of the valve (i think !) on the pierburg one anyways..

[Ga73]

Hi thassos,

It's a good theory and I'll try and look into that.
I'm now also thinking maybe the pressure control valve wiring after reading other threads.

It's an absolute rabbit hole this, one I don't want to go much further down 😔