Can I improve MPG?

[Tully]

Hi Everyone

I've recently joined the Forum with my first Citroen, a 2003 C5 2.2HDi semi-auto.
I enjoy the car but I'm quite disappointed with the relatively poor mpg, especially compared to my last car, a Saab 9-3, also a 2.2 Diesel.
I've put this down to one reason, agree/mock at your leisure

*The turbo kicks in at 2500rpm*

I'm no engineer so bear with me - 2500rpm in top gear = 75mph. With the turbo spinning this "takes the weight", as it were, off the engine. This delivers approx 45-55mpg.
At, say, 2000rpm the engine is doing all the work with no help from the turbo, resulting in 28-35mpg or thereabouts.
This means it's more economical to drive at 75-80mph than it is at 55-60mph.

Ok, to the point (please.... )
Using a Lexia, or something similar, can the engine management system be reprogrammed for the turbo to kick in at 2000rpm?

Ha...I know you're all going to say "just drive faster then"

Best regards

Tully

[qprdude]

2.2 not known to be frugal and almost certainly won't match the Saab for mpg. I swapped a 9-3 1.9 TiD for a C5 X7 and the mpg is way down. On a 500 mile trip, I got under 40 mpg, admittedly with a very heavy right foot. No doubt there are ways of getting a better return but don't expect miracles. Someone will be along soon to help.

[Chlorate]

I am an engineer I'll have a bash.

The answer is not easily I'm afraid, the ECU doesn't tell the turbo to come on at a certain engine speed, I think in this case the ECU probably just meters the fuel to compensate for boost and controls the operation of the wastegate (i.e. limiting boost pressure).

Turbocharger selection is a bit of a pain really, it's all to do with available energy in the exhaust gas and how much air you want to compress with it. It's very difficult to get a fixed geometry turbocharger to work all the way through the rev range of an engine, you can have a "little" one that spins up low in the rev range and runs out of puff higher up, or a bigger one that takes longer to kick in but gives more high end performance.
This is getting a lot better with variable geometry turbochargers, but they have their own problems...

Back to the point, there are clever ways to tweak your engine map to get more boost lower down. This is usually done in modified SI engines by burning more fuel and retarding the ignition to bring the exhaust energy up (i.e. wasting a bit of fuel to help the turbocharger spin) thus doesn't help fuel consumption.

There are other ways of doing it of course...like a better exhaust or bigger valves or reported cylinder head or even a better matched turbo - but of course these are all rather expensive and would take some time before you'll see any return through fuel savings.

Alex

[Lighty]

My 3.6 litre Porsche RS does 30 mpg at a steady 85 mph

[Peter.N.]

I have just sold my 2.2 for that very reason, I drive very gently and couldn't get much more than 40 mpg from mine, I did about 100 miles in my 2.0. yesterday with an average consumption of 58.9 mpg. I rest my case.

Peter

[qprdude]

My 3.6 litre Porsche RS does 30 mpg at a steady 85 mph

Problem is,your 3.6 litre Porsche is beyond the means of many C5 owners due to tax and insurance costs.

[citroenxm]

I have just sold my 2.2 for that very reason, I drive very gently and couldn't get much more than 40 mpg from mine, I did about 100 miles in my 2.0. yesterday with an average consumption of 58.9 mpg. I rest my case.

Peter

[waynedance]

I have just sold my 2.2 for that very reason, I drive very gently and couldn't get much more than 40 mpg from mine, I did about 100 miles in my 2.0. yesterday with an average consumption of 58.9 mpg. I rest my case.

Peter

[stu9]

If I got about 50 from mine (2.0hdi) I'd be happy

[Tully]

Thanks for all your input guys. Guess I'm just stuck with it. 75mph everywhere then.....

[Peter.N.]

If I got about 50 from mine (2.0hdi) I'd be happy

Move to the country and get lighter boots

Peter

[KP]

A good full service can help a little, also maybe a remap so as to adjust when the turbo kicks in. IIRC the 2.2 turbo on my dads kicks in a bit lower than that. at 1-1.5k revs its a bit slow but then picks up rather quickly... 3rd gear wheel spins aren't hard in slightly moist conditions

Also it could be needing an italian tuneup??

My dads 2.2 isn't doing much worse on fuel than his old HDi90 that i have now he says although its had its DPF removed. Don't forget as these clog up they will strangle the engine so maybe taking it off and washing it out would help a little as more air able to flow through will help the turbo be able to spin up much quicker.

Consider sticking in a little biodiesel say, 1-2litres per fill up to help flush and clean the engine out a bit more. make sure its good stuff though!
And then dont forget the odd long run. if we had an unlimited autobhan for 50-60 miles i'd say sit on that at 115mph for 20mins to get it upto red hot temps and clear the combustion chambers and turbo out from all the gunk that builds up.
The EGR valve will also be sapping power and coked up as well wo maybe worth finding out where it is, removing it and blanking it off/disabling it once you clean it out.

[qprdude]

Not the mph needed for temperature is it? You can sit at 60 mph in a lower gear. Does the same job.

[Bandit12]

I bought my first citroen which is also my first ever diesel a few weeks ago. A 2002 C5 2.2 estate and this explains why I was getting such low mpg around town yet on a long run mpg almost doubled. Was thinking it was me but now I know otherwise. Thanks guys. The car and mpg are still much better than the Mk2 mondeo auto it replaced.

[Peter.N.]

I investigated every option to improve my mpg with no success, I even fitted a tuning box, went like a train but no improvement in fuel consumption. If you look on the Peugeot sites people have the same complaint with the 2.2 406, possibly 1 in 10 owners claim to get 50+ mpg most of the others moan about poor fuel consumption, may be a few of these are good on fuel but they are the exception rather than the rule.

Last year coming home from Scotland I got 67.8 mpg over 650 miles from my 2.0 Hdi 406, the best I ever had from the 2.2 C5 was 50, that was driving at a steady 60 mph on a flat motorway, my average 2.2 consumption was less than 40 mpg, my 2.0 C5 is showing 54.4 mpg.

Peter