C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

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skycat61
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C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Hello All,

I'm not sure if I should be starting a new topic for this but it doesn't quite seem to fit in with what I've found on this site.

The car is a C5 2.2 HDi 136 Auto that is 10 years old with just 57K on the clock. I am getting what I consider to be very poor economy from it, that is it returns 25.4 MPG on my standard weeks journeys to work. This compares to my previous MK1 C5 2.0 Petrol Manual which would return 27 MPG over the same journey. I sort of thought that this diesel, my first diesel, would do rather better.

When accelerating from standstill (below 1500RPM or so) there is no grunt but eventually after a couple of seconds the turbo kicks in and it pulls reasonably well. It will quite happily reach cruising speeds of 100+ MPH (private test track, honest).

There are no engine warning lights or messages on the multifunction display.

I have checked that the swirl actuator is working correctly - it goes to all the right places at all the right revs. Is it possible to visually check the operation of the turbo modulator in a similar fashion?

I have purchased a clone lexia with software but I cannot get the software to run without crashing so I have no idea of what fault codes are present on the system.

Does somebody out there with a nose for a problem have any idea what might be wrong?

Donald
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Peter.N. »

Try unplugging the MAF and see if it makes any difference, if it doesn't it could be faulty. I had a 2.2 C5 but found the fuel economy very poor compared to the 2.0. I was getting around 40 mpg compared with 55 mpg on the 2.0. so I changed it for one, most of them seem to be poor although occasionally you hear of someone getting 55 mpg but its the exception rather than the rule, mine was manual of course you are going to do considerably worse with an auto, especially when cold.

The swirl flaps make very little difference, they are an emissions device rather than a performance/economy one.

Peter
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Thanks Peter.

I will give that a try. I should point out that my work journey is a 12 mile run and I average a speed of just 20 MPH. I've driven a few other diesels and they do seem to pull much better at low revs which was why I was wondering if the turbo modulation system was functioning properly.

Donald.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Peter.N. »

I must admit the power was quite good from my 2.2 so that doesn't sound right, it was just the fuel consumption I couldn't tolerate. You are obviously not going to get good consumption on that sort of journey, most of mine are rural or motorway and I can easily get 60 mpg+ from my 2.0. 406 but I don't drive much over 60 mph. To check your consumption try and find a quite stretch of flat road that you can do a steady 60 mph on, I would think you ought to get 40-50 mpg under those circumstances but try checking or changing the MAF first. Sometimes they just get oiled up, if that's the case you could try spraying the sensors with carburettor cleaner but don't touch them, they are very delicate.

Peter
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Yes. I'm not expecting wonders in terms of MPG with that journey but I do feel it ought to be a little better than the previous C5. I have unplugged the MAF and taken it for a quick "acceleration test" on a local hill where the speed topped out at about 60. Engine was at normal operating temperature. It did not seem to make any difference if the MAF was connected or not. I have not done any economy testing with the MAF disconnected.Should I?

Thanks and best regards

Donald
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Peter.N. »

Hi Donald

The only effect I have experienced with a faulty MAF was lack of low down grunt which improved dramatically when I changed it. I bought a secondhand genuine one off ebay, I am told that the cheap new ones don't last.

Peter
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by myglaren »

Try giving the MAF a squirt of carburettor cleaner - did wonders for mine recently - no effect on fuel economy though.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

The 2.2 drinks fuel when cold, the whole system is geared to getting the engine to warm up as quick as possible tricks like switching on electrical consumers e.g heated windows etc so loading the engine are used, even so at 12 miles depending on traffic etc it will only be just about up to an ideal running temp. On a 16 mile journey where the first 3 miles are town driving then the next eight are undulating country roads followed by a final 5 miles Motorway thrash I could get 33mpg by judicious use of the throttle..
Lately mine has the symptoms you describe not sure if it is a problem with the box / torque converter or the turbo as the box is long overdue for an oil change, however given the mileage I suspect that the FAP is getting a bit choked up which may affect the ability of the turbo to spool up, the other possibility is the calibration of the pedal sensor, mine being a Mk1 has a cable between the pedal and pot which stretches so there can be a bit of lost motion at the bottom end. The mk2 the the pot is on the bulhead pretty well at the end of the pedal at the bulkhead but it might be worth investigating the calibration of this / checking for lost motion etc.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by myglaren »

^ With that in mind a bloody good Italian tune-up might be called for.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Peter.N. »

The increase in fuel consumption when cold is quite amazing, I did a test when we were on holiday in rural Scotland with the 2.0. Hdi 406, in the first 5 or 6 miles of gentle driving it was returning around 50 mpg but by 10 miles is was up around 60 mpg.

It was quite cold at the time and the auxiliary heater which comes on at less than 10c is drawing something like 150 amps, that's quite an additional load on the alternator although the first couple of miles were downhill so we got free heat for that period. 8-)

The ambient temperature makes quite a bit of difference to the overall consumption, my average is around 53-54 in the summer but drops to below 50 in the winter.

Peter
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Many thanks for the comments. I can see that the car would use more fuel when cold but on my 12 mile journey the engine is at normal temperature after 4 miles so I'm inclined to think it may not be that.

When people say they get 40-50 MPG just make me feel more that something is amiss. I'm getting 25MPG and average speed of 20MPH.

I've had the MAF off the car and while the airflow elements looked clean the thermistor was a bit gunky. I cleaned it with IPA as I've heard the carburetor cleaner can leave residues. I also got the lexia working and so was able to check that the MAF sensor was giving sensible outputs. I had a flow rate variation 188mg/cp at tickover and 600mg/cp at about 2000RPM unloaded. I suppose I believe its OK. The temperature sensor said it was 19 Celsius which disagreed with the external temperature sensor which read 3 Celsius.That just might be correct given the engine bay was warm.

What I could do with at this point is some guidance in using the lexia to diagnose this. Anyway I cleared all the faults and I'll have another look in a week and see if MPG improves in the meantime

Many thanks again

Donald
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Paul-R »

Is the car an estate or saloon? If it's an estate then that can knock a few mpg of what everyone expects or quotes. And being an auto won't help.

It sounds as if your car might be giving towards the low end of what would be considered "right". The C5 is a heavy car and stop-start driving, especially at the beginning of journey when it's cold, is not going to be good.

My C5 is an 2.0HDi manual estate. During the week I drive 7 miles to work and then back in the evening. There's a certain amount of stop-start and a couple of miles of motorway. In the summer I get low to mid 40s to the gallon. It's worse in winter and at the last fill-up it worked out at 36.9mpg. Now that is worse than normal and I think the MAF might be on the way out again.

The type of journey and whether it's summer or winter has quite a large effect. In the summer and touring around I can get nearly 50mpg. The very best I had last year was 49.4mpg. The worst last year in winter around town was 35.9mpg.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Peter.N. »

I think my mpg figures are not what the average driver would get, we live in a rural location and our nearest town is 7 miles away so we never do really short journeys, we rarely get stuck in traffic either. My average consumption is a bit over 50 mpg in the summer and high 40s in the winter except on long journeys where 65 mpg is fairly easily obtainable but I have a very relaxed driving style and rarely exceed 60 mph or 2000 rpm.

When my son borrows the car even the long journey mpg can go into the mid 50s and he doesn't drive particularly hard but still manages to knock 10 mpg off what I get. If I drove like I did in my youth I would probably only be getting 30 - 40 mpg.

The 2.2 seems to use disproportionally more fuel than the 2.0. and being auto is going to make it worse, the best engine for economy, emissions and reliability is without doubt the 8 valve 2.0.

Peter
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Thanks to all those who have posted their experiences with C5 fuel consumption. It's very useful to make the comparisons. My C5 does seem to be top of the pole for poor MPG. Perhaps it is just the urban cycle I do, but I've noticed that motorway MPG isn't up to much either at about 32MPG. Of course this is West Yorkshire and there are no level roads :-D

I've got the fresh faults from the lexia this morning after a 15 mile local journey (24.9MPG, ave speed 16MPH). There are 5 faults in total:-

INJECTION P0568 - Temporary Fault. Cruise Control Signal Control Stalk in short circuit or open circuit

GENERAL D209 - No communication with auto gearbox. Data invalid.

GENERAL D209 - Dialogue with gearbox ECU incorrect value received.

GEARBOX P0706 - Permanent Fault. Multi-function switch coherence.

SUSPENSION P05D2 Temporary Fault. No communication with the steering wheel angle sensor incorrect value received.

I haven't really played with the cruise control yet so I'm not sure if it works properly. Just occasionally the auto gearbox refuses to change up to 4th gear when it should, again not sure why. Also the steering wheel is not quite straight when the steering is set to straight ahead. I can't see anything in this that is screaming poor MPG. :(

Donald.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Paul-R »

skycat61 wrote:Perhaps it is just the urban cycle I do, but I've noticed that motorway MPG isn't up to much either at about 32MPG.
If that's using the MPG display then it can easily be wrong. Before I broke the button on the end of the wiper stalk (press, press, press, - oh it's not working any more) and could check the computed fuel consumption I found that it was always pessimistic compared to my accurate MPG figures from fill up to fill up. I only ever used the instantaneous MPG figure as wagging finger to tell me I was working the engine too hard.

In fact - are your MPG figures based on the display only or using the method above? If the former then you could just be worrying about nothing.