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

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

Post by skycat61 »

There are no Injection ECU fault codes set for the EGR valve Richard. The main problem seems to be that the Gearbox ECU is not managing to talk to the other systems reliably. Anyway, all diagnosis has stopped for the time being as my lexia laptop has caught a virus and the Lexia program now crashes every time it is run.

I had a go at reseating the Injection and Gearbox ECU connectors over the weekend but it doesn't seem to have helped.

Donald.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

I've now had all the brakes checked for binding and they are all just fine so I can now discount that as the problem. I've got the Lexia software reinstalled and working too and the current list of faults are:-

RADIO - Permanent Fault. Auxiliary audio input no 1

INJECTION - Temporary Fault. Cruse control signal control stalk is short circuit or open circuit

ABS - Temporary Fault. No communication with the auto gearbox Data invalid

SUSPENSION - Permanent Fault. No communication with steering wheel angle sensor Incorrect value received

GEARBOX - Intermittent Fault. Multifunction switch coherence

DIRECTIONAL HEADLIGHTS - Remote Fault. Temporary Fault. Dialogue with gearbox ECU Incorrect value received

TYRE DEFLATION - Remote Fault. Temporary Fault. Vehicle speed information incorrect value received

I think there are four independent faults here:- the RADIO is nothing to worry about, the cruise control and steering angle sensor are probably no big deal, but there are the ABS, HEADLIGHTS and TYRES that are getting duff information as a secondary fault and it looks like the gearbox is the source of this misinformation.

So I used the Lexia to monitor the gearbox and all looks very sensible, that is, the input and output speeds make sense, the temperature is reasonable at 75 Celsius, and the gear position lever makes sense even if you move it very slowly between positions.

I understand from the gearbox control information I've gathered that the gearbox drops into fallback mode if something is wrong with its sensors, and might supply an invalid token to other systems that rely on it, but I'm at a loss to understand whats going on. So three questions..

1. Should I just replace the multifunction switch and hop all becomes right?
2. Is there a way to use the Lexia to see if an ECU is in fallback mode?
3. Why do the directional headlights work even if the steering angle sensor is faulty?

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

Post by cachaciero »

On the gearbox you need to monitor the Torque converter params check that it locks up when it should. However all these faults except one are intermittent or temporary (same thing really).
The gearbox switch coherence would appear to be a real problem when it happens and changing it will probably resolve it BUT none of this addresses your low down performance and high fuel consumption issues I think you will have to look else where for that. Might be worth using the Lexia to monitor manifold pressure that should give you some idea as to how well the turbo is working, also pressure across the FAP also the o/p from the MAF you might be able to set the Lexia to record these parameters as you are driving (depends on the Lexia and Software) if you record speed as well it may show something.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Thanks Cachaciero. The Lexia I'm using is 3.45 and I cant see how to get it to record and graph parameters. I can't even find the torque converter lock-up status in the parameters. Is there a newer version of the software available? My Lexia came with a copy of Diagbox but unfortunately it will not install on the computer.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Have now learned to use the graphing facilities (they don't make it obvious) and decided to check if the torque converter lock-up was working. The data showed that lock-up was occuring at some points in the short journey with the engine rpm almost identical to the auto input speed rpm within a few rpm which could easily be measuring uncertainty.
The speed graphs were all continuous (no dropouts) which I suppose means the sensors are working fine.

So, what to do next?
cachaciero
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

O.K the lockup would appear to doing what one would expect at least under one set of conditions, time to start looking at the engine parameters suggested previously, the parameter recording facility will allow you to record five parameters simultaneously as I remember, but like I said you may find that you can't do that with the engine parameters, time to find out :-) As regards Diagbox there is some good info under the relevant heading on this site.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

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

Post by skycat61 »

Thanks for that cachaciero. Xantom's comment about low end performance sound just like mine:-
Only thing is the initial acceleration from rest, that's still poor until the turbo kicks in so starting across junctions and roundabouts is never relaxing. I'm sure it shouldn't be like that, I've driven other cars with torque converters and they had decent bite and acceleration at low revs.
I'll be looking at the engine parameters soon but in the meantime I found this (http://www.pug306.net/forum/threads/149 ... st-the-MAF) on the web regarding MAFs. It states that with a working EGR and at tickover the MAF should read 250-300mg/r and if it reads below 250mg/r it may be the EGR is jammed open. For my C5 the MAF reads 188mg/cp at tickover.

Would a jammed EGR cause the poor MPG and low end grunt problem?
Monkeyfeet
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Monkeyfeet »

Open /partially open when it shouldn't be normally gives some smoke - ie when booting it after poodling in town stop/start. In a manual you'll notice "juddery-ness" lower down the revs, when you might be otherwise in a higher gear.
So, yes, sometimes imho with this engine.
But no egr fault codes anyone?
cachaciero
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

I would expect the EGR valve to be pretty well wide open at the lower rev ranges so really if stuck open I would only expect it to have an effect under higher revs / power demands. The function of the EGR is to reduce NOX components by reducing the amount of surplus oxygen & Nitrogen in the combustion space, at low -mid revs / power demands.
Without EGR there would be far more oxygen available than required to ensure combustion of the injected fuel and Nitrogen plus Oxygen at high temps produce various NOX related products. The injection of an inert gas reduces the amount of oxygen and what is exhaust gas but inert. Frankly on the C5 I've always thought that they would have been better of taking it off the downstream side of the FAP and feeding it in to the low pressure side of the inlet, that way there would be no carbon particulate being re-injected which when you examine the inlet side of the engine makes a right mess.
The more I think about this I can't see that at the lower power ranges the state of the EGR valve having much effect on the MAF reading. The MAF is on the low pressure side of the turbo and the EGR is on the high pressure side and even at idle the Turbo is / should be blowing a little and the Turbo flow would be the main driver for the MAF. Seems to me that if the MAF o/p is as low as it is at idle that it has to be a prime candidate for attention.
I also come back to something looked at earlier what does the Leixa say about the accelerator pedal at idle?. If the idle position is too low then that could explain both the low MAF value and poor pick up, not sure what calibration of the pedal sensor is possible on the Facelift :-(
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

I've just managed to get some screen shots of the engine/gearbox/egr/fap. Each shot is a separate run around the block (1 mile) on a warm engine. Sometimes I got to boot it :-D but most times it was urban driving. All I need to know now is how do I upload the screen shots to this site.

Cachaciero: Many thanks for the input on EGR operation: as I'm not a car mechanic this is all learning curve for me. I checked the Lexia for the pedal sensor reading and it went from 0 to 99.5% but I have not in any way checked its linearity. I must admit I don't understand whats going on with EGR valve demand traces as they seem to mainly bang from wide open to completely shut.

Donald

https://www.dropbox.com/s/qqoukkvex2q2m ... x.bmp?dl=0

https://www.dropbox.com/s/3rht5jkyy5tby7d/egr.bmp?dl=0

https://www.dropbox.com/s/g725jpo4a6uknhw/fap.bmp?dl=0

https://www.dropbox.com/s/952adqdadje5r ... n.bmp?dl=0
Last edited by skycat61 on 02 Mar 2016, 23:44, edited 3 times in total.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

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Here is a guide to posting images on this forum.
cachaciero
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

O.K The EGR valve is vacuum driven the level of vacuum is controlled by an electrovalve which is an on or off device, so if that is all you have then you have either max vac (open) or the EV is closed which just puts ambient air pressure onto the EGR ie closed. Now if you pulse the EV between open and shut then the level of vacuum on it's output will be proportional to ration of "on" time and "off" time.
What you are seeing in the Lexia trace is the on / off pulses as you can see the on /off times change, this tells you that at least the ECU is driving the EV in a believable manner, whether the EV is actually doing anything is another question and for that you will need another essential piece of maintenance kit a pressure gauge capable of displaying vacuum. You need a gauge some suitable sized flexible piping and some small plastic joiners / T pieces,
The idea is to disconnect the output line from the EV and connect the T piece in and then connect the T to the pressure gauge, now you will be able to see the vacuum changing (or not if the EV has failed :-).
However from your Lexia graph the thing that strikes me is the turbo pressure I don't think it is right. This graph is absolute pressure, as such 1000mb (millibars) is normal ambient and the Turbo never seems to go above 2000mb, my feeling is that it should go higher.than 14psi boost which is what 2000 equates too.

EDIT Normal range would appear to be between a few millibars above ambient to about 1800 mB

The Turbo is a variable geometry device refer the data I sent you the modulating sleeve is driven by vacuum same as the EGR uses and identical EV to do the job. The ECU does have the ability in theory anyway to check that the turbo pressure corresponds to that commanded but I don't know for fact that it does, but I doubt it.

EDIT The ECU computes a desired value for Turbo Pressure and the actual turbo pressure is measured the Lexia displays both parameters and the should match, if the ECU sees actual pressure higher than the computed target value by some amount it will trigger limp mode.


I do know that it checks turbo pressure for overpressure, under which case it will put the engine into limp mode.
As a quick check I would suggest disconnecting the vac pipe that runs from the turbo EV to the turbo, leave it in the breeze then check pressures with the Lexia. You could go for a drive in this state and see if it,s better, in this case the turbo should be in max boost mode so it is possible that if driven in this state you could reach an over-boost condition which would cause the system to drop you into limp mode. If this makes the low end better then you need to find out why the turbo is being held down in low boost mode, don't drive it into overboost more than you have to as it is my belief that the pressure can get high enough before it drops to limp mode to blow the inter-cooler.

EDITED to clarify some things for posterity :-)
Last edited by cachaciero on 01 Apr 2016, 08:46, edited 1 time in total.
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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 »

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

Post by cachaciero »

Done some more looking at those Lexia traces, maybe the turbo pressure is not so bad as I thought. I think that what it would be good to see is a plot of accelerator position (which we can use as a reference) MAF Turbo pressure, demanded torque (from the gearbox) and engine torque and see if that gives us any clues. I have to say that at the mo I still favour the MAF. The problem with much of this is that while we can measure lot's of parameters we don't know what the relationship between them is exactly because that is all contained within the "engine model" in the ECU which of course only Citroen know...(maybe!) But I do know that accelerator position is used to calculate a demanded engine torque value. (RPM will equate to torque and load)
Torque at a steady state rpm will be basically a function fuel and air in, so I would expect the ECU to be able to calculate the amount of boost required to achieve the "air in bit" and and the amount of fuel to inject. Presumably under steady state conditions the Turbo is driven until the "air in" (MAF) value is achieved but it won't be quite as simple as that because I am sure that in real time the delta changes in MAF are used to trim the fuel injected, it will get even more complicated because around all of this the ECU is also calculating various emission control parameters. Dynamically accel / decel adds another layer of complexity.

What is really needed for this kind of exercise is a series of snapshots of various key parameters from a good engine, i.e level road 30 mph Torque=xx MAF-yy Fuel=zz boost=bb and the same at 0mph and maybe 40mph with that kind of data it would make trouble shooting far easier, but I have never seen such a source of data, though I am sure that it exists...anybody??

Thinking further about the EGR valve while I would expect it to be open at idle or light throttle where little fuel is going into the engine however on an acceleration demand I would expect instantaneously a lot of extra fuel to be injected the burn requiring more oxygen and hence less EGR so I would expect the EGR to close to some degree under acceleration, if it did'nt then acceleration would be poorer and there would be a lot more black smoke due to incomplete combustion. It's quite obvious from the Lexia graphs that the ECU is quite actively attempting to modulating the EGR whether that is really happening we don't know because the system does not measure actual EGR valve position.
I think that in order to eliminate the possibility of a sticking EGR valve it would be a good idea to blank it, off this can be done simply at the front of the engine where the stainless EGR pipe connects to the inlet manifold, simple steel blanking plate.under the flange,

I will emphasise one other point, the correct operation of the EGR and Turbo on these engines is critically dependant on having good vacuum, a leak anywhere in the system can have a negative effect so a check that the vac pump is working and that the vacuum is actually being held really needs to be checked quite early on in the trouble shooting process.
It should be noted that using the Lexia the EV's can be "manually" operated so using it with a vacuum gauge attached the Turbo modulation and the EGR valve can be checked for leaks when the valves are operated.