2004 C5 estate 110 HDI fuel economy

[howiedean]

Hi,
I'm getting around 38 - 39 mpg doing a mix of motorway and A road driving (70 - 80 mph), this drops to 32 if I'm doing city driving.
The fuel/air filter are new and the emissions test was fine for the MOT.
The brakes are not binding therefore any suggestions as to why the mpg is so low?
I had thought about replacing the MAF although I'm not getting any smoke under acceleration.

Regards,

Howie

[Citroenmad]

One of our 2.0HDi 110s had a dip in economy for a while. I replaced the MAF with a genuine new Citroen unit and economy was restored. At first no codes were stored, but after a while a code was found but no warning light ever appeared.

I generally clean the MAF on every service with electrical contact cleaner spray, it usually improves things. I also give a good spray of air intake cleaning spray through the intake system. Ive just been out tonight in the 110 and did that, performance has restored and hopefully mpg will increase slightly too.

Has your economy got worse or has it always been the same?
Is that the actual economy or what the trip says? As they are not often the same thing.

[howiedean]

One of our 2.0HDi 110s had a dip in economy for a while. I replaced the MAF with a genuine new Citroën unit and economy was restored. At first no codes were stored, but after a while a code was found but no warning light ever appeared.

I generally clean the MAF on every service with electrical contact cleaner spray, it usually improves things. I also give a good spray of air intake cleaning spray through the intake system. Ive just been out tonight in the 110 and did that, performance has restored and hopefully mpg will increase slightly too.

Has your economy got worse or has it always been the same?
Is that the actual economy or what the trip says? As they are not often the same thing.

The mpg on the trip computer was reading 32mpg which I noticed after purchasing the car. I've not checked the mpg by brimming the tank although it is using a fair bit more than my previous Xantia HDI cars.

Regards,

Howie

[Paul-R]

You need to do a brim to brim test - several are better. The indicated MPG figures should only be used as a guide - brim to brim is the only accurate way to check.

[Peter.N.]

My 406 Hdi estate is averaging nearly 50 mpg with a best of over 60 mpg, but I do live in a rural area and don't drive very fast or hard.

Peter

[timborob]

Hi,
I'm getting around 38 - 39 mpg doing a mix of motorway and A road driving (70 - 80 mph), this drops to 32 if I'm doing city driving.
The fuel/air filter are new and the emissions test was fine for the MOT.
The brakes are not binding therefore any suggestions as to why the mpg is so low?
I had thought about replacing the MAF although I'm not getting any smoke under acceleration.

Regards,

Howie

I have had my C5 110 VTR for around a year now and can assure you 32 mpg would be about right for short town/city use as mine has gone as low as 28mpg.

On a run to Cornwall late last year I did manage 62 mpg which was confirmed brim to brim test.

If i were you i would reset the trip computer on the next fill by holding the button in the end of the stalk and see what you are actually getting from it.

[den169]

I live in the pennines so all hills and get 39 knocking about and 52/53 on the motorway at 70mph.2003 sx 110bhp estate

[howiedean]

I live in the pennines so all hills and get 39 knocking about and 52/53 on the motorway at 70mph.2003 sx 110bhp estate

Thanks gents. I'm thinking that either I have a problem with the MAF or EGR system; there are not fault codes registered, can anyone concur?

Regards,

Howie

[timborob]

Hi,
I'm getting around 38 - 39 mpg doing a mix of motorway and A road driving (70 - 80 mph), this drops to 32 if I'm doing city driving.
The fuel/air filter are new and the emissions test was fine for the MOT.
The brakes are not binding therefore any suggestions as to why the mpg is so low?
I had thought about replacing the MAF although I'm not getting any smoke under acceleration.

Regards,

Howie

Hi Howie

Just trying to clarify how you are getting your MPG figures :

You say you are getting 38-39 mpg on a mix of motorway and A road
and this drops to 32 mpg in the city.

Are you measuring by the trip computer average MPG display section
or looking at the constant MPG display and trying to get an average?

When i first collected my car the average MPG display was showing just over 28 mpg but after i read up on how to reset it the first MPG figure displayed after brimming worked out to be 31 mpg which was all from city/town driving .

If you are watching the constant MPG section it will not give you an accurate enough reading to go by.

If you are resetting the trip computer properly before doing free flowing A road and motorway work at 70-80 mph then I'd say your MPG of 38-39
is abit on the low side and you should be around the 45 MPG mark but that also depends on how you are using your throttle


Obviously its a good idea to get both the MAF and EGR valve checked out
but it doesn't sound too serious to me especially your figure of 32 MPG for town work as that's on par with mine and as i said i have done over 60 MPG confirmed.

[howiedean]

Thanks for your responce Tim and I have answered your questions:

Just trying to clarify how you are getting your MPG figures :

You say you are getting 38-39 mpg on a mix of motorway and A road
and this drops to 32 mpg in the city.
35 mpg as a combined figure.

Are you measuring by the trip computer average MPG display section
or looking at the constant MPG display and trying to get an average?
The trip computer at the moment.

When i first collected my car the average MPG display was showing just over 28 mpg but after i read up on how to reset it the first MPG figure displayed after brimming worked out to be 31 mpg which was all from city/town driving .
Mine was showing 32 mpg when I first got the car.

If you are watching the constant MPG section it will not give you an accurate enough reading to go by.
No the overal mpg figure.

If you are resetting the trip computer properly before doing free flowing A road and motorway work at 70-80 mph then I'd say your MPG of 38-39
is abit on the low side and you should be around the 45 MPG mark but that also depends on how you are using your throttle

I have seen these mpg figures when driving as you have described.

Obviously its a good idea to get both the MAF and EGR valve checked out
but it doesn't sound too serious to me especially your figure of 32 MPG for town work as that's on par with mine and as i said i have done over 60 MPG confirmed.
[/quote]
I replaced the MAF sensor a couple of days ago and will see how I get on. GSF sold me a dodgy cheap one first although this performed as though it was not plugged in. It seems to drive slightly better with a new expensive MAF sensor. I think that my previous Xantia HDI Estate performed better than the C5 in both performace and mpg terms. It seemed to return good mpg regardless of how it was driven.


Regards,

Howie

[Citroenmad]

Your right in that the C5 2.0HDi will feel a little slower and use a bit more fuel than the same engine in the Xantia. The C5 is a bigger car and its a bit heavier too, though performance and MPG should still be good for a 110bhp in a bigish car.

Our 52reg 2.0HDi 110 hatchback C5 has a pessimistic MPG trip computer, it UNDER reads by 3-4MPG without fail. It usually averages 40.9 on the trip, which works out to about 44-45MPG - this is mixed driving, town work, short trips, longer motorway trip etc.

If sticking at motorway speeds of 70ish MPG is around 50 (actual)

I would brim the tank and calculate it the correct way before deciding its MPG computer is correct, they very rarely are.

When I was using a 2.0HDi 110 daily I would get 45-46MPG (actual) on average - displayed as around 42 on the trip computer.
My 138 2.0HDi is much more accurate and does around 48-50MPG with my current commuting and general driving. More can be had very easily if driven gently.

[cachaciero]

Our 52reg 2.0HDi 110 hatchback C5 has a pessimistic MPG trip computer, it UNDER reads by 3-4MPG without fail. It usually averages 40.9 on the trip, which works out to about 44-45MPG - this is mixed driving, town work, short trips, longer motorway trip etc.

If sticking at motorway speeds of 70ish MPG is around 50 (actual)

I would brim the tank and calculate it the correct way before deciding its MPG computer is correct, they very rarely are.

.

Food for thought

IF the MPG from the trip computer differs markedly from values calculated from odometer mileage and fuel taken on board then you have an injector problem.

Rational:

The Trip computer uses the same distance info as the odometer and distance as displayed on the trip computer and odometer agree within 0.1 of a mile over 600 miles, at least in my case 600 miles being the distance that I have so far tracked.

Fuel consumption, the Injection ECU knows and needs to know exactly how much fuel it is injecting into each cylinder to ensure correct combustion, the fact that it does have a value of the amount of fuel that it "believes" is being injected can be seen on a Lexia.
If the value that it believes is being injected is the actual value then the trip computer can sum this value which will be a true and accurate representation of the fuel consumed between resets of the trip computer

Ergo the value of the fuel used over any distance displayed by the trip computer and the values obtained by calculation should be as near as makes no difference identical.

The Injection system will calculate the amount of fuel that needs to be added for each combustion cycle and then taking into account the fuel rail pressure open the injector for a time period required for the injector to pass that amount of fuel.
Now if you have followed me so far you will understand that the ECU has to make one assumption and that is an assumption that the Injector conductance characteristics are what it believes them to be.
You will be aware that when fitting new injectors they have to be fitted as a set AND you have to tell the ECU what class they are this information is what the ECU uses to calculate the conductance of the injector i.e amount that the injector will pass.
Now if there is a problem with the injector i.e it passes less than or more than the ECU believes it is passing then the amount of fuel consumed on each cycle will be less or greater than the ECU believes is being passed.

Therefor the fuel consumption figure as calculated by the trip computer will be in error when compared with a value calculated based upon the a measured amount of fuel consumed from the tank.

As I said at the beginning if the two values do not agree then it is because there is a problem in the injection system, could be injectors could be rail pressure sensor and maybe a few other things that I have'nt thought of, so if the two values don't agree ask yourself why? and the bigger the difference the more urgent this becomes.
Don't assume that the trip computer is inherently inaccurate it isn't in the sense that it calculates very accurately the amount of fuel that should have been used which as I have shown may not be the amount that has been used.

cachaciero

[Citroenmad]

Actually I know that my above mentioned C5 2.0HDi 110 has not got an injector problem. I know its previous owner who had the car from almost new, they also reported the same discrepancy in the MPG readout as I have found and they have never had it any different, its never got more out of phase shall I say, always 3-4 MPG under reading. My previous 2.0HDI was also out by a similar amount.

Ive yet to find a trip computer which is extremely accurate, usually they differ slightly, not just Citroens but other brands too. I find the C5IIs very close to the actual, if not spot on. Of course the actual is never really the actual but from brim to brim is a very close calculation and for the difference to be the same each fill up is evidence.

Have you ever checked your C5s actual MPG from brim to brim?

[cachaciero]

Have you ever checked your C5s actual MPG from brim to brim?

No can't afford all that money in one hit . and to do it properly it means draging a can of smelly diesel around.

However if I did I have no doubt that it would not agree with the trip mpg simply because I have little doubt that after a 110K plus miles and never having been re-calibrated the injector characteristics will not be as they were when fitted so the amount that the injection ECU "thinks" it's putting through the injector will be in error. However I do keep a tab of what goes in and how many miles i get out of it on a running basis and the difference is not that great, the trip tends to be optimistic by about 1 / 2 mpg which is what I would expect

Doesn't change my rational, viz the fact that the trip reads different is not a fault in the trip calculations per se it's a calibration fault of the injection system.
You say you don't have an injection fault but how do you know? have you had the injectors out recently and calibrated? have you checked that the rail fuel pressure is correctly calibrated? have you checked the fuel temp sensor is correctly calibrated? suspect not.
We all of us only get worried when we perceive that consumption is excessive or more likely when there is a performance deterioration. The difference between the trip and brimming it is put down to an error in the trip rather than a small deterioration in injection performance which is the more likely culprit.

There are quite a few people who report very close agreement between the two figures so there are engines out there which do consume very close to their designed criteria.

cachaciero

[Citroenmad]

True, a C5 HDi fill up is between £90-£100 at the moment, depending on how much the fuel is and how low the tank was. That is a noticeable amount! Mind, it does last a good few miles.

Well im not convinced, but there you go. We seem to disagree about a few things at times

Why bother getting the injectors re calibrated when the car is fine?
I was asuming the injectors are fine regarding your theory, as its trip computer has always been out since the car was new, i doubt it had injector problems then and doubt it does now. Any main injector problem usually causes a rattle at rist, its running very sweetly with no rattle, loss of performance or MPG drop. Im very happy with its 45MPG.

Besides, surely if its actually doing better MPG than the trip says, how does that suggest an injector is at fault or not calibrated. You would think it would inject more fuel, not less

Anyway, all of this is really besides the point I was initially making, its a valid point to check the actual MPG and see how or if it differs to the trip reading.