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

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

Post by cachaciero »

jsp wrote:12 mile run only?? The engine oil is just warmed up at the correct temp. Cruising is best for a diesel driving around town no car is going to eco. drive.

I suggest you measure your oxygen sensor to see if it is working correctly not all faults will be present in Lexia.

I did a remap on my relatives 407sw 2006 2.2 hdi and 45mpg easily.
Manual or auto? The auto box fitted on this engine is close to it's power handling capacity @136BHP so re-mapping the engine for more power runs the risk of early box death.
On the motorway 45mpg on a manual is not difficult without re-mapping. Even a standard 2.2 auto in good mechanical state can achieve 40-42 on a good motorway run, lightly loaded.

There's no doubt in my mind that the car is best suited to long haul motorway work which is why I use the Prius for most of my driving these days :-)
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jsp
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by jsp »

Manual. They only sold a few hdi autos here in NL.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Hmm. I'm fairly sure that my Haynes manual says that the turbo boost is either 1.1 bar or 1.3 bar on the 2.0L HDi. I take this to be gauge pressure so an absolute turbo pressure of 2.2 bar seems quite reasonable to me. The Haynes manual has no info on the 2.2L HDi. :(

I understand that the EGR (and the turbo) electro-vales are driven with a PWM signal to provide proportional control of the actuators. The EGR control signal spends by far and away most of its time saturated at full on or full off. To me this is indicative of a control loop that has been opened by a fault. i.e. that the forward loop gain is no longer being moderated by feedback. If any element of this loop is "stuck", e.g the electro-valve or the vacuum driven EGR valve, then negative feedback is lost and proportional control could not be achieved; the demand signal would bang from full on to full off or vice versa as the control variable passed either way respectively past the set point. I'm not sure what control variable(s) the EGR system monitors. Is it the lambda sensor? And why can't Citroen/Bosch publish a block diagram of the control strategy of the engine management system? :(

I suppose my next move is to check if the EGR is actuating properly in response to a demand input from the lexia. I'd much appreciate some guidance about how this is done. Does the engine need to be running? Can the position of the EGR be seen externally? Can the lexia demand intermediate positions?

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

Post by Hell Razor5543 »

I would advise that, here on the forum, the Haynes books are known as Haynes BoL (Book of Lies), as they sometimes are not exactly accurate (for example, the book for the series 2 Xantia shows the way to replace the front foglight bulbs is the same as for the series 1. This is definitely NOT correct!), so I would be inclined to double/triple check the info, especially if it could cause damage if you get it wrong.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Thanks James, I must admit there is a paucity of good information regarding the performance of the 2.2 HDi as Cachaciero has pointed out previously. I double checked Haynes and the boost for the 2.0L is 1.2 bar, but your definitely right that I should proceed carefully....
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

Well this thread has caused me look harder at the EGR operation than I have had to for a long time :-( There was something else in the Lexia traces that had me going WTFIT! so dug out the Bosch description of the system a copy of which I sent you and after a little perusal I remembered something that I last had a look at at about 6 years ago !
On the front of the Inlet Manifold there is a Y shaped bit of manifolding and in each arm of the Y there is a butterfly valve (vac controlled via an EV) now one leg goes to the O/P of Intercooler (cold air) and the other goes effectively to the I/P of the intercooler (hot air). Now it was my understanding that when the engine was cold the butterfly were modulated such that the inlet air temp was kept high for quicker warming up. However it would appear that they also play a part in the EGR circuit as well quite how or why I hav'nt got my head around yet but look at the EGR description in the Bosch HD152C doc I sent you.
When looking at the EGR Lexia trace you can see that up to the 70 second mark the Exhaust gas Recycling THROTTLE EV open cycle ration is about 50 % what 50% means I am not exactly sure but my belief is that it means that the PWM of the EV is equivalent to 50 % valve open.then we can see it goes max open at about the same time as the fuel flow is increased, presumably acceleration, from there on it bangs about between max open and shut, this valve is the cold air inlet to the manifold. The interesting thing about this is that it stays in step with turbo pressure which seems to change in steps. Now ask yourself what happens to turbo pressure if the inlet manifold is blocked? the pressure will rise. Unfortunately we don't have a trace for the other manifold valve to see if that is opening and closing in step if it is not then effectively the inlet manifold could be being blocked, however measured airflow would tend to suggest that this is not the case. We would be able to deduce more if we had either accel; position or rpm as a master trace.
The two manifold valves like the EGR are all driven by vac via EV and PWM and like the EGR there is no way of knowing from the Lexia if they are actually doing what they should!
For testing these valves Citroen / Facom have a very nice tool which has a built in vac pump and gauge, undoubtedly expensive! To test them the Lexia has a menu line Actuators under the same heading as Parameters but you still need a vacuum, you can get this by running the engine or plumbing in an external vacuum source if you have one, The noise from the engine can make it difficult to hear the click from the EV's and the EGR but i managed! The two butterfly valves can be visually inspected if required by taking off the rubber hoses and using a mirror or even ones fingers !
From this lexia traces as far as can be judged the MAF looks good in general terms i.e turbo pressure increases flow increases and the turbo pressure matches the reference pressure, however this doesn't mean that baseline MAF o/p is correct, it would be nice to know what the value should be at idle.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Its starting to get quite complicated. :) Worse than that the lexia seems to only display the state of three of the electrovalve's command signals:-

1. Exhaust Gas Recycling Throttle Electrovalve
2. Exhaust Gas Recycling Valve Electrovalve
3. Turbo Pressure Electrovalve

...and I'm not sure what is what when compared to the BOSH manual diagrams. The diagrams suggest to me that there are in fact TWO throttles:- one drawing air from before the intercooler through a preheater, and one drawing air from after the intercooler. Both these are controlled by electrovalves but the lexia doesn't make clear which 3 of the 4 valves it's actually displaying.

Anyway, I took the car for a thrape up and down the by-pass with what valves it could display, boost, air flow and RPM. Engine was semi warm to start with and total journey about 6 miles. The by-pass is a fairly steep hill.

https://www.dropbox.com/s/xtgf9izt8a0bo ... 2.bmp?dl=0

I've also purchased a vacuum test gauge though I'm currently thinking that the main vacuum pump and reservoir are probably functioning fine because the turbo boost via the modulator electrovalve seems to be working ok. I might have a play with it this weekend but I note that the throttles are vacuum to CLOSE which I take to mean don't start the engine with them disconnected.

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

Post by cachaciero »

If you are talking disconnection in the sense of vac disconnected then running the engine disconnected is fine, in fact it might be instructive to run the engine with the cold air butterfly valve disconnected (but blank of the vac pipe). The vac system is divided up into different areas so because one bit is o.k doesn't mean that the rest is. Trawl through this site search on my name and read about the saga of swirl valves as I re-call I wrote a bit about vacuum and how it could change depending on where the leaks were.
the exhaust Gas Recyling throttle valve is the butterfly valve of the cold air side of the heat exchanger No 2 is the actual EGR EV and 3 is the EV controlling the Turbo Pressure Modulation in the turbo.

From your Lexia traces I think we can take it that the Turbo is working o.k but it seems to me that the EGR is partially open when I would have expected it to be closed i.e rpm above 2500 and we come back to the Throttle Valve it might be interesting to repeat your last test but substitute ambient air temp for the turbo EV and coolant temp for air flow(we know that that corresponds to turbo pressure quite well)
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

I repeated the test drive on a warm engine with parameters you suggested (correct pic uploaded):-

https://www.dropbox.com/s/sz53xyazvl3pz ... 3.bmp?dl=0

Something else that is concerning me is that when the engine is not running the air flow reads about 190mg/cp. Surely this should be zero or close to it? Put it this way, the highest air flow reading I've seen is about 1400mg/cp so the MAF has approximately a 14% FSD offset. Presumably with this error the injection system would be supplying a rich mix by about 14%?
Last edited by skycat61 on 10 Mar 2016, 22:50, edited 1 time in total.
cachaciero
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

I think maybe you have put up the wrong Lexia trace, looks like one of the earlier ones.
Re MAF yes that is a concern, as I said before the flow changes correspond nicely with turbo pressure changes, however that doesn't prove that the actual values are correct it would be nice to know what the values should be at 0 rpm and say 2000rpm car stationary not in gear.
The thing I don't know the answer to is this is the Lexia reading "RAW" MAF data or is it reading corrected data, given the way the MAF sensor works I would have expected some automagic zero calibration at switch on and having said those magic words yes at zero rpm I would expect the flow to be 0. which ever value is being displayed It might be worth reseating the connector on the MAF to see if that changes the values, might also be worth cleaning the MAF with a propriety carb or manifold cleaner to see if it makes a difference. As far as I can deduce I would expect the MAF to read about150 at idle plus minus 10 percent and yours seems to be much higher than that, which ties in with the offset.
Worth looking at this thread http://www.frenchcarforum.co.uk/forum/v ... =3&t=38058.

Reading a specialist tuning site they regard MAF calibration failures extremely common on older / high mileage PSA HDI's so it might be worth just changing it anyway on the basis that if it's not the problem today it will be tomorrow and it might be a quick way of resolving your current problem :-)
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Ooops! Sorry about that Cachaciero. The link has been changed to the correct trace now. Yes, I think its probably time to try a new MAF. A job for this weekend though I'm still not sure why that electrovalve is banging wide open and shut all the time. The lexia has the the valve described as:- "Exhaust gas recycling throttle electrovalve open cycle ratio", but I don't know what this refers to on the diagram on page 17 of the Bosch HDI EDC15C2 Injection System document you sent me. The other electrovalve on the trace is described as "Exhaust gas recycling valve electrovalve open cycle ratio", and it would be nice to know what that referred to on the Bosch diagram as well.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Gibbo2286 »

I wonder if too much emphasis is being put on Lexia and not enough on visual inspection here.

Some of the problems you are experiencing can be caused by simple stuff like perished vacuum hoses, difficult to see without a very careful examination.

I've found often that the thin hoses linking the vacuum pump, the electrovalves, the EGR and the turbo actuator can have almost invisible cracks that make the whole system go pear shaped.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

Gibbo2286 wrote:I wonder if too much emphasis is being put on Lexia and not enough on visual inspection here.

Some of the problems you are experiencing can be caused by simple stuff like perished vacuum hoses, difficult to see without a very careful examination.

I've found often that the thin hoses linking the vacuum pump, the electrovalves, the EGR and the turbo actuator can have almost invisible cracks that make the whole system go pear shaped.
I agree about the vacuum pipes, this engine control system runs on vacuum as much as electricity which is why I suggested taking a vac gauge to it. As you point out hairline cracks in pipes are difficult to see and that's when you can actually see the pipe !
A vac gauge plugged in will give you a good indication of whether a leak actually exists or not and if it does by using the gauge and isolating bits of the system it becomes quite easy to locate where the leak is occuring.

The Lexia is brilliant when you know how to use all of it's facilities and I would start with it every time, however on the 2.2 particularly the fact that say the EGR EV has the signals expected does not mean that the actual EGR is responding. The Lexia has no way of knowing EGR position, because there is no position feedback from the actual valve unlike later systems where the EGR valve does have a position feedback sensor which the Lexia can see. So for final confirmation of what the Lexia is suggesting Mk1 eyeball and or ears are very important.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

skycat61 wrote:Ooops! Sorry about that Cachaciero. The link has been changed to the correct trace now. Yes, I think its probably time to try a new MAF. A job for this weekend though I'm still not sure why that electrovalve is banging wide open and shut all the time. The lexia has the the valve described as:- "Exhaust gas recycling throttle electrovalve open cycle ratio", but I don't know what this refers to on the diagram on page 17 of the Bosch HDI EDC15C2 Injection System document you sent me. The other electrovalve on the trace is described as "Exhaust gas recycling valve electrovalve open cycle ratio", and it would be nice to know what that referred to on the Bosch diagram as well.

Exhaust gas recycling throttle electrovalve Item 1 on the drawing item 26 being the actual butterfly valve.

"Exhaust gas recycling valve electrovalve item 4 on the drawing, item 7 being the actual EGR valve.

The throttle valve 26 is together with the "Inlet heater throttle " valve item 22 modulating the air inlet temperature to the engine, as one closes the other valve of the pair from the hot side should be opening to achieve / maintain an ideal inlet air temp.
I am guessing that the operation of these two valves is mapped to revs and temperature, where at low revs / power the predominate controller is temperature and at higher power the predominate controlling factor will be revs incorrect operation would I believe substantially impact both acceleration and fuel consumption. If for example the "hot valve" was always open then at higher power demands the effect of the intercooler would largely be nullified this would increase fuel consumption markedly. If the "hot valve" was permanently shut or partially shut then as the "cold valve closes" inlet air would be markedly reduced and acceleration would suffer.
As I write this I do wonder if the often reported poor fuel consumption of this car is due to incorrect operation of these two valves. If the hot valve was stuck in some intermediate position then both acceleration and fuel consumption would suffer. There is a double wammy to this in that I believe that the operation of these valves at low revs will depend on the same temperature sensor as is used for mass flow calculations i.e the temp sensor in the MAF.
Looking at your latest Lexia trace this sensor seems to be saying that over your test drive the ambient temp was varying between 5 and 20 degrees is this possible?
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by jsp »

I don't know if it is allowed to put a ''blanking plate between the EGR tube'' in the UK.

Here we do them a lot on pre 2006 cars as they don't need a E-OBD test on them at the MOT.

Yes I have a lot of HDi's here on maintenance at my work and they do fail a lot EGR's.