C5 X7 - here's a challenge - identify the culprit?

[steveclv]

So my C5 2.0 HDi 138 auto has a fault. When giving it the beans, as the car gets towards the red line it throws a code - P0088 which is excess high fuel pressure. No other symptoms leading up to it apart from a very occasional slight stumble but no error codes.
So the diagnosis lists the possible errors as
-Engine ECU (Software not up to date)-- no, very unlikely
Poor fuel or polluted fuel (petrol, deposit, etc.)-- no, always use good fuel
Problem on the fuel low or high-speed circuit (hose, tank, diesel fuel filter, etc.)-- already changed to a new Bosch filter
Fuel injectors -- not leaking and run injector cleaner through to see if it made any difference - it didn't
Engine fuse box -- no evidence of any corrosion
Electrical harness -- unlikely
Connectors -- unlikely
High pressure fuel pump -- possibly?
Fuel high pressure sensor -- possibly?

So here is my dilemma. I have Diagbox but I don't know which values to monitor and how to diagnose which component it might be because
a) A fuel pump is around €500
b) A fuel pressure sensor is around €500 (it's factory fitted to the manifold so you buy a new manifold and injector pipework)
c) What isn't mentioned is a Fuel Pressure Regulator around €100 but maybe that they assume it's part of the pump

Does anyone know how to monitor specific values and procedure to determine which component might need to be replaced?

The fuel pressure hits 1820bar (max 1800) when the error occurs at 4250rpm

Thanks for any pointers

[kantica]

Maybe high pressure regulator ? Citroen part number 193339. This is part of the high pressure pump, but can be bought separately, manufactured by Delphi, same as the high pressure pump.

[steveclv]

Yes, that's item (c) in my list.
The issue is that I don't want to just replace item by item - I'm sure there is a step by step process that mechanics follow in order to identify which item has failed - I just don't know what it is

[Jay-Bruce]

Maybe high pressure regulator ? Citroen part number 193339. This is part of the high pressure pump, but can be bought separately, manufactured by Delphi, same as the high pressure pump.

This.

A failing pump would cause low pressure, a failing sensor would only see an incorrect pressure, but failing regulator wouldn't be able to displace the excess fuel from the rail being pumped in there by the fuel pump, so logically, it's most likely the regulator rather than anything else.

[Mihael_M]

The previous thinking is logical and makes sense. In addition, the pressure regulator is cheaper and easy to install.

[steveclv]

OK, you have convinced me LOL - I will change out the regulator and see if that fixes it - as you say it's relatively cheap and your logic makes sense plus it's also the "easiest" (hahaha) to change. I just need to get some more 1/4" extension bars.
Thanks

[steveclv]

So, am about to change the Fuel Pressure Regulator however is there any special procedure apart from keeping it all very clean? Does the pump need priming etc afterwards?

[steveclv]

Quick update - tried to do the job myself but ancient eyesight, fat fingers and a general uncertainty about breaking our only car led me to use a local garage. They only charged me an hours labour but insisted on supplying the part rather than use my Aliexpress €45 one (which looked identical to the part they used). I paid the premium of having a genuine PSA part rather than a pattern one.
So job was done so I fired up the OBD2 scanner and ran live data on Fuel Pressure Sensor and booted it hard with max acceleration - fuel pressure peaked at 1550 bar - no dash lights, no P0088 or P1199 so PROBLEM SOLVED.
I still have the 1570L9 Fuel Manifold with the Fuel Pressure Sensor as it looks as though that is not needed so will probably stick that up on eBay

Oh happy days

I did notice that the car felt a little slower but seems to be more economical - that all makes sense as no doubt the failing FPS was overfuelling.