Low MPG On Xantia 2.1TD SX

timbo101 · Post by **timbo101** » 03 Jun 2008, 16:39

Hi all,
I am getting slightly concerned about the low MPG I am getting from my xantia MK1 estate 2.1TD sx.
I am getting about 28 mpg around town which I dont mind too much as the what car magazine says it should return 30mpg but I was expecting to get much better results on a long run which I am not.
We did a 250 mile round trip on the weekend to London and back and I got 290 miles on £50 worth of Diesel. Diesel round here is £1.30 per litre so I make it about 33 miles to the gallon.
I know it is a big engine but I was hoping that being diesel it would return better results especialy as the fuel prices are getting so stupidly high.
Can anyone comment on any suggestions on if this is normal or if there is anything I should do.
Many thanks....Tim

Post by **myglaren** » 03 Jun 2008, 16:53

That is rather high. The 2.1 is reputedly more economical than the 2.0.
I'm not satisfied with my economy but I recently acheived 633 miles on a tankfull. It wasn't completely dry when I refilled, it had used 63L, within the constraints of filling accuracy.

Xaccers · Post by **Xaccers** » 03 Jun 2008, 18:21

Are you driving it with a purpose (foot down to get up to speed) or like a steam locomotive ("it'll get to 70 eventually, so why hurry?")

The most I got out of my 2.1TD was about 32mpg driving it like a 1.9TD (where I'd normally get 45mpg).
Jim now has it and he gets around 50mpg although has a totally different driving style to me.

Leaving the battery disconnected for an hour or so (probably doesn't need more than 30 mins but I was watching telly) seemed to help as this reset the ECU.

C.J. · Post by **C.J.** » 03 Jun 2008, 18:35

Xac wrote: Leaving the battery disconnected for an hour or so (probably doesn't need more than 30 mins but I was watching telly) seemed to help as this reset the ECU.

What's that all about then?
Is this some new way of decreasing the fual consumption that I've never heard of? Tell us more!

Post by **CitroJim** » 03 Jun 2008, 20:20

C.J. wrote: What's that all about then?

The ECU is adaptive. It learns your driving style. Power it off and it forgets. It then needs to be retrained over a 15 mile drive under varying conditions.

Mine has learned I'm one who likes to save fuel

I've been to Somerset and back today and under very mixed and difficult conditions (including queuing on the M25 for 10 miles) it averaged 50mpg.

Pootling around town working as a taxi for my girls and running to work and back sees low 40s mpg easily.

I'm the first to admit I let it reach 70 in it's own time and the end of the throttle pot has cobwebs on it but I really don't hang around; I practice driving for economy..

Whereabouts in Dorset are you Tim? I might be able to call in one day soon and do a diagnostics session for you.

timbo101 · Post by **timbo101** » 04 Jun 2008, 08:20

hi jim. Well he that is the case i will definitely reset the ecu first as when i first got the car i did drive it a bit hard as i did like having he extra power at first but now i drive to save fuel rarely going above 2000 rpm.i live in poole in dosset jim but can travel a bit as would love to have it checked over and thanks for the offer of your help. I love the way all the citroen owners quick together and are so helpfull . Many thanks . . Tim

Penguin · Post by **Penguin** » 04 Jun 2008, 08:23

** STUPID QUESTION ALERT!! **

Do all diesel Xantia's have the 'learning' ECU or just the 2.1? My 1.9 is not as economical as I would like and as I haven't had it long maybe the previous owner was somewhat leaden footed?

C.J. · Post by **C.J.** » 04 Jun 2008, 08:46

Sorry. I must be a bit dim too. I'm struggling to understand this one.
Are you saying that the ecu adapts, and gives you better fuel consumption if you drive like a granny all the time, but you've got to disconnect the ecu first to clear its memory before doing so?
What happens if you occasionaly give it a 'heavy boot' then....disconnect again after, or it'll think Lewis Hamiltons driving it, by giving you an extra 200bhp?

bigjl2 · Post by **bigjl2** » 04 Jun 2008, 10:08

The 2.1 has an ECU and, I think, drive by wire throttle from what I have read and been told, the 1.9 is old school mechanical injection, and would probably respnd to and air and fula filter change and a good italian tune up.

Penguin · Post by **Penguin** » 04 Jun 2008, 12:39

bigjl2 wrote:The 2.1 has an ECU and, I think, drive by wire throttle from what I have read and been told, the 1.9 is old school mechanical injection, and would probably respnd to and air and fula filter change and a good italian tune up.

Cheers, that's a shame as I have already done all of that.

MikeT · Post by **MikeT** » 04 Jun 2008, 15:35

ECU's respond to changes monitored by the sensors. One such sensor is the throttle position sensor (TPS) which is directly controlled by you, the driver. Therefore, the ECU will adapt, to a degree, to your driving style as it goes about it's merry way trying to keep the engine running efficiently and safely.

If you've renewed the filters, oil, etc, then perhaps the injectors are in need of a service? One tip I picked up from here - drain the fuel filter and pour in neat injector cleaner.

Does your engine have EGR? From what I can tell, they are the work of the devil and should be disabled at the earliest opportunity! Filthy little bleeders

timbo101 · Post by **timbo101** » 05 Jun 2008, 07:55

hello again. I have seen in loads of places on here about disconnecting the egr but how do i do that please . Please bare in mind that i foot know what anything does under the bonnet so please be specific . Many thanks . . . Tim

Penguin · Post by **Penguin** » 05 Jun 2008, 09:23

I know what the EGR is and what it does, but have no idea whether I have one or not! If you disconnect it doesn't it have a detrimental effect on the emmissions causing you MOT problems??

Penguin

Post by **CitroJim** » 05 Jun 2008, 09:50

Penguin wrote:If you disconnect it doesn't it have a detrimental effect on the emmissions causing you MOT problems??

No, not on what is tested on the MOT. Only smoke density is measured on a diesel, hence why you don't need a CAT on a diesel to secure an MOT pass.

EGR is there to reduce NOx (Oxides of Nitrogen) emissions. It does this by lowering peak combustion temperature by recirculating a small amount of exhaust gas into the inlet charge.

You can easily defeat it by pulling teh vacuum hose from the actuator. On a 1.9TD this is a lantern shaped device on the RH side of the exhaust manifold linked to the inlet manifold via a shiny concertina pipe. Mosre or less ditto for the 2.1 although the concertina pipe can be seen on top of the inlet manifold between No. 2 and No. 3 inlet manifold runners.

Timbo: We'll make arrangements for a diagnostics. I'll let you know next time I'm down that way. Don't worry if we find a needle lift sensor fault - "They all do that sir.."

In the meantime, give your 2.1 a really good service and check all the sensors are connected. The one to check especially is the MAP sensor which is a small square box down by the side of the intercooler. It connects to the intercooler via a small rubber pipe which may be perished or letting in air. Similarly, check all the turbo hoses for leaks, especially the one that runs underneath the engine. It can be pin-holed trough an accidential grounding.

Finaly, driving style. The 2.1TD is an old-school diesel that develops loads of torque low-down. It's all finished by 3000rpm and it's pointless to rev it above this. Keep it between 1500 and 3000rpm and don't try to hurry it. Feather back the accelerator when up at cruise so that you have just enough acceklerator on to maintain speed. Trying to thrash a 2.1 is non-productive. Drive it in a relaxed style and they're brilliant. They're very laid-back and don't like being rushed

Penguin · Post by **Penguin** » 05 Jun 2008, 10:13

citrojim wrote: You can easily defeat it by pulling teh vacuum hose from the actuator. On a 1.9TD this is a lantern shaped device on the RH side of the exhaust manifold linked to the inlet manifold via a shiny concertina pipe.

So I would simply pull off this hose? Would I need to blank it or leave it open (I'm thinking blanking is required?)

I think I might give the injector cleaner a go. So.. open the valve to empty out the diesel from the filter, remove the top cover, close the valve, fill with injector cleaner (any recommendations?) fit cover top back on, start engine and let it idle away?

Sorry about the stupid questions but I am rather mechanically inept!