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

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

Unread post by 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
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Re: C5 X7 - here's a challenge - identify the culprit?

Unread post by 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
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Re: C5 X7 - here's a challenge - identify the culprit?

Unread post by 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
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Re: C5 X7 - here's a challenge - identify the culprit?

Unread post by Jay-Bruce »

kantica wrote: 19 Oct 2024, 20:41 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.
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Mihael_M
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Re: C5 X7 - here's a challenge - identify the culprit?

Unread post by Mihael_M »

The previous thinking is logical and makes sense. In addition, the pressure regulator is cheaper and easy to install.
steveclv
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Re: C5 X7 - here's a challenge - identify the culprit?

Unread post by 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
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Re: C5 X7 - here's a challenge - identify the culprit?

Unread post by 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?