C5 2.0.Hdi 8 valve, fuel computer?

[Peter.N.]

My readout has been telling me that the car is averaging around 55 mpg, the last two fill ups I checked on a full tank only to find that its only doing about 45 mpg What could make it so inaccurate?

The speedo reading is unusually spot on by the sat nav, the mileage I'm not sure about but it seems about right. I thought it wasn't doing what it said because I was only getting about 700 miles from a tank of fuel, my 406 with the same engine will give over 1000 miles and the readout agrees with that.

It is stuck in limp home mode, wont rev above 3000 rpm but that doesn't bother me because I very rarely use that many revs, could that have something to do with it? There is no black smoke.

Any suggestions. My Lexia is not working at the moment.

Peter

[isisalar]

Hi Peter
Can only speak from personal experience on the Xantia. The speedo reads almost exactly 10% over across all speeds compared to the sat nav readout, could point towards your speedo over reading, possibly tyres a bit too small?
Two things have improved the running and fuel consumption of mine recently, a few miles at high (4000)rpm in third, and a dose of slick 50 fuel system treatment, together with V power.
You'll need to clear the limp mode for the former but the latter might even help there too.
Cheers
Paul

[Peter.N.]

Hi Paul

The speedo is spot on, its the only car I have had that is, checked 100% against the satnav. The readout showed 60.1 mpg when we went to Scotland last year which I thought was OK as the 406 averaged well over 60 mpg, confirmed by fuel used, the year before, when I filled the 406 after a long journey the available mileage reads well in excess of 1000 this again is confirmed by the amount of fuel I put in, I had never done a brim to brim test on the C5 until a couple of weeks ago and they showed something between 43 and 49 which is very poor compared with the 406.

I will have to persevere at getting my Lexia going and see what it shows.

Peter

[SaabC5]

I found i lost about 4mpg when my 2.2 went into limp home mode. Could be even more noticeable with the 2.0HDI

[jgra1]

yes would agree with saab. limp mode cant be the most efficient Peter?

I have a lex but am not down your way in the near future. did you ever get yours installed?
John

edit just saw your lex comment,,

I wonder if you could courier your lap to someone on here who can get the lex working.. I am happy to try but am not the most software savvy on here

[Peter.N.]

Limp mode obviously isn't helping but it doesn't come in until nearly 3000 rpm and I rarely reach those dizzy heights. My Lexia suddenly stopped talking to the computer, it says it can't connect although the light is on. I have deleted the programme but am having trouble re loading it. There are several videos on Youtube but the photo's are so fuzzy I can't read the writing.

My main concern re the fuel consumption is why the display is showing about 10 mpg more than it is actually doing, the one on the 406 is pretty spot on.

Peter

[Northern_Mike]

If you want to send it to me, as Jgra suggests, I'll gladly fix it, test it on my C5 and send it back.

Sent from my GT-I9300 using Tapatalk

[jgra1]

nice offer Mike,

Peter, think the limp may put all 3000 rpm in a different map, so even the lower speeds may suffer,., not sure, just a feeling..

I can hardly drive mine in limp.. unless a flatish motorway.. otherwise its hard work..

[Peter.N.]

Mike

Thanks very much for the offer, I may well take you up on it if I don't have any success in the near future, I will have another go at reloading it when I have the time to do it without panicing.

jgra

The performance below 3000 rpm is excellent, as good as it ever was, it just comes to a brick wall when you get to about 2800 rpm. My 406 has a different problem, it has no power below about 1800 rpm and then suddenly it takes off, but no lights on. I have noticed a slight increase in fuel consumption since that happened but not very much, may just be due to the cold weather.

Peter

[Chris570]

Quite odd as when my (Xantia) 110 HDi went into limp it was a pig at all RPM's and as you say a brick wall at 2800rpm.

I agree with the others here and say get the fault cleared first.

As for the trip, the ECU might just put out it's fuel consumption data based on what it is seeing input wise, so from that it would deduce it's normal map would inject x amount of fuel and give y amount of power giving z consumption. If it's not using the right map then the whole lot will be kicked right out.

[Peter.N.]

That sounds feasible Chris, had not thought of it. I will concentrate on getting the lexia working - or using someone else's.

Peter

[Peter.N.]

I disconnected the MAF sensor on the 406 and it drives fine now!

Peter