Horrible fuel economy C5 II 3.0V6

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AlvinCitroenC5
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Horrible fuel economy C5 II 3.0V6

Post by AlvinCitroenC5 »

So I have replaced all the coils and spark plugs since I had a #2 coil fault awhile ago and the fuel economy continues to be very high. In fact, it is now higher than before. Dinner owning the car and having driven it for about 1000 km so far the fuel economy avg at 21 L / 100 KM or even higher. I barely get 280 km of range with one tank.

I have no other fault code relating to the engine and when I drive it hard the power is good all the way to redline with no power gaps or stutter. And the idle seems stable.

What should I be looking for? Ex: What range sound the O2 sensor be before the cat?

Thank you all for your suggestion and help.
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Zelandeth
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Re: Horrible fuel economy C5 II 3.0V6

Post by Zelandeth »

That works out to around 14mpg if my math is correct.

What sort of driving are you mostly doing? That figure doesn't seem unreasonable for an engine that size if there's a lot of city driving or short runs involved, they're really most at home on the open road, cruising at a mostly steady speed.

If you're on the open road though and cruising, yes I'd expect a lot better economy then though.

I've no experience with this particular engine, but I'd probably be checking for a sane output from a coolant temperature sensor (it will over-fuel if the ECU thinks the engine is colder than it is), before condemning expensive bits like oxygen sensors.

Given the complexity of the power unit here getting it hooked up to a Lexia to have a look at the live data is probably going to be the best approach, otherwise it'll likely end up being a case of randomly throwing expensive parts at it and hoping for a solution.
Current fleet:
06 Peugeot Partner Escapade 1.6HDi, 88 Renault 25 Monaco, 85 Sinclair C5, 84 Trabant 601S, 75 Rover 3500, 73 AC Model 70.
AlvinCitroenC5
Posts: 109
Joined: 16 Apr 2017, 00:10
Location: Hong Kong
My Cars: 2005 Citroen C5 II
x 3

Re: Horrible fuel economy C5 II 3.0V6

Post by AlvinCitroenC5 »

I do have a working Lexia Pp2000. Since there is no fault code, where in Lexia can I read the coolant temp sensor output? And what output range / voltage should the reading be when the engine has warmed up / coolant temp gauge needle move to the middle position? Thanks.
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