C5 2.0HDi 2007, excessive fuel consumption when accelerating

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Jogren
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C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Jogren »

Hello,

Citroen owner from the north of Sweden here. New to the board - hello all!

I have the following symptoms with my C5:
When accelerating the fuel consumption goes through the roof. Normally it would be hard do get it above 10 liters per 100 km, now it's over 25 l/100km and that's when driving carefully. However, when driving in cruising speed the consumption seems to be normal. (I'm not quite sure how you measure in the UK? Mpg? It used to be 28mpg or above, now it's under 11mpg when acc.)

The engine sounds and feels "raw", like it's struggling. (This might be me overthinking stuff, after noticing the fuel consumption thing..)


I have 3 permanent fault codes:
P1351 Pre/post heating relay circuit. Plugs never supplied.
P1614 Speed limiter hard spot switch. Coherence of the sensor voltage.
P1644 Speed limiter hard spot switch. Open circuit or short circuit to positive.

I have used Lexia and the FAP PSA app (the one from Amazon) to look inte the DPF, and it seems it tries to regenerate very often - once per 20 km. DPF soot is at 26%, which doesn't change after regeneration, and cinder value goes up to 10% but that value goes to 0 after regeneration.
I noticed that the values regarding Eolys didn't change, so I suspected that no Eolys was added to the tank, and that this had been the case for a while.
When trying to run the Eolys pump with Lexia I got the response that the action was not possible.


What I have done so far:
I have topped up the Eolys with Walker 167. When trying to reset the values in Lexia, nothing happens and the values stays the same.
Despite that, I took the car for a ride and did a forced regeneration. (Not the one where it goes up to 4000rpm on neutral for 5 minutes. The other one, where you drive the car more than 60kph for 10 minutes.)
This took the cinder value down, but soot stayed the same.

I've also changed the air filter. A change was due, 2 years since last time. Haven't been able to test drive the car after that.

Fuse no 5 (DPF/Eolys) in the engine fuse box is ok.


So, any ideas? I'm thinking:
Eolys pump malfunction?
DPF ECU malfunction? (But I do get readings from it, it seems.)
Glow plugs malfunction, leading to lower exhaust temp = no regeneration?
EGS valve stuck and/or backed up?


Best regards

Johannes
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Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Peter.N. »

The only reason I can think of for that sort of consumption is restriction of the air supply, does it smoke when accelerating? Is the turbo producing the normally accepted power? It certainly could be an obstruction in the exhaust, a clogged DPF for instance. You really need a Lexia to give you the full info.

Peter
Jogren
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Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Jogren »

The new air filter didn't change anything.

The engine seems to have as much power as before, and there's no black smoke. (As far as I've seen anyway.)

I do have a Lexia, but I'm not really sure what to look for?
I do suspect there's something off with the DPF, since it's regenerating very often. And, I can't test run the Eolys pump - Lexia tells me that action is not possible. So, no Eolys in the diesel = no regeneration = lots of soot in DPF?
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Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by GiveMeABreak »

The P1351 Pre/post heating relay circuit. Plugs never supplied. fault is common on the C5 HDi - so unless on with another related fault, can normally be ignored.

But with the other 2 faults - I'm wondering if your accelerator pedal is duff and could be sending incorrect data.
C5 II Accelerator Pedal.PNG
1601 Q4 (Left Hand Drive) - but I'd need your VIN to double check, is the one with the speed regulator

A failed sensor can be the cause of poor fuel economy - have a quick look here that explains it:
https://www.yourmechanic.com/article/sy ... ion-sensor
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Marc
Jogren
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Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Jogren »

1601Q4 is the one, according to service.citroen.com.

But, the fault code states that it's the speed limiter switch that's malfunctioning. Do you think that can cause my problems?
Jogren
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Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Jogren »

When driving the gas pedal % seems to be reasonable.
Peter.N.
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x 1199

Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Peter.N. »

Is your engine temperature normal? They will use a lot of fuel when cold.

Peter
Jogren
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Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by Jogren »

According to dashboard instruments and Lexia, engine temp is normal. Coolant renewed when I changed the timing belt this summer.
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GiveMeABreak
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C3 1.6 HDi Exclusive Aluminium Grey (The Silver Hornet)
C5 MK II 2.0 HDi Exclusive Obsidian Black
C5 MK I 2.0 HDi SX Wicked Red
Xantia S2 2.0 HDi SX Hermes Red
C15 Romahome White
XM 2.0 Turbo Prestige Emerald Green Pearlescent
XM 2.0 Turbo Prestige Polar White
XM 2.0 SX Polar White
CX 20 Polar White
GS 1220 Geranium Red
CX 2.4 Prestige C-Matic Nevada Beige
GS 1000 Cedreat Yellow
x 5646

Re: C5 2.0HDi 2007, excessive fuel consumption when accelerating

Post by GiveMeABreak »

I shouldn’t of said that this is the right part for the C5 with speed regulation fitted. The reason I suggested this is because it had a ’kick down’ zone, on the accelerator pedal that overrides the speed limit setting in an emergency when you may need to overtake quickly. That along with the poor fuel economy as per the article I linked to. The other cruise control faults can be linked to a faulty break switch.
Please Don't PM Me For Technical Help

Marc
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