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 »

The car is a hatchback and yes I'm using the MPG meter which bears out the increased number of times I'm having to fill up The statistics for the last tank full are as follows:- 288 miles traveled, ave speed 18MPH, display says 24.3MPG while brim to brim gives 24.05MPG. I think that's near enough for my purposes.

I've never had a car with a drink problem before. Maybe its been in an unhappy relationship or feels its life is going nowhere. Perhaps counseling is required at this point? In any case, it needs to cut down. :-D
Peter.N.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Peter.N. »

My 2.0. C5 is just the opposite, its giving the same readings as I would expect to get from the 406 but when you do a brim to brim test its actually about 10 mpg worse. Never have been able to sort that out, I think its injector problems and I have a spare set here but have no got round to fitting them yet.

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

Post by cachaciero »

IF you have a marked discrepancy between MPG as indicated by the computer compared by calculation and very very carefull measurement of fuel in (don't believe the pumps!) then you have one of two problems either and injector problem or wheel / tyre size is incorrect.

The error messages quoted suggest that the CAN bus comms are not as good as they should be, Engine ECU, Gearbox ECU, and COMMS 2000 unit are all on the same CAN Bus, surprised the ABS isn't there as well if the engine / autobox comms are not consistent then I believe this could have a marked effect on fuel consumption and acceleration not only will this affect gear selection but it will affect the torque converter "lock up" program i.e the converter may not lock up at all = higher fuel consumption or stays locked up when it should'nt - poor acceleration probably more noticable from low speed.

I would look for a bad connection somewhere in this loop try re-seating all the connectors on the Engine ECU, Gearbox ECU BSI. This of course does assume that the Lexia clone? is good and not prone to lying.
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Sloppysod
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Sloppysod »

My old 2.2 hdi auto would give me a regular 40 (isH) to and from work (13 miles each way), drop down a bit in town, 30-35. then I fitted a gadget that reduces fuel pressure when the throttle is steady and the consumption reduced to by about 3-5 mpg, on a run I could get it above 50 mpg (it ended up a game) at 70-75 mph.

skycat61 - Have you checked the rear brake callipers, they are attached to the vehicle with long bolts through the aluminium calliper into the steel bracket and are susceptible to dissimilar metal corrosion, this makes the brakes bind and the pads wear to a wedge shape. Remove the bolts, clean the mating surfaces, smear both surfaces with instant gasket (I used blue Hyloma, but others are available) then bolt back up. You may need new pads so be aware.
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Paul-R
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Paul-R »

Sloppysod wrote:...then I fitted a gadget that reduces fuel pressure when the throttle is steady and the consumption reduced to by about 3-5 mpg, ...
That's counter to what I would expect. Increasing the injection pressure gives finer atomisation (normally) which in turn allows better combustion and therefore more power or better fuel economy. I'm at a loss to explain it.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

OK. Just an update on the MPG having cleaned the MAF. The round trip to work and back is 23miles @ ave speed 20MPH gave an consumption of 27.9MPG, an improvement of 2.5MPG. So a tiny bit better but still poor.

Cachaciero
I'm confident that the car has the right size wheels and tyres as the distance it gives for the work run is correct. I have no idea how one might check the injectors. Is there any advice you could give me? The same goes for the communication faults - can the Lexia be used to test the CAN bus?

Sloppysod
Straight after I drove home this evening I measured the brake disc temperatures using a pyrometer. Three of them measured about 25 degrees Celsius, but the off side rear measured 46 degrees Celsius making me believe I have some binding on that wheel. Ambient temperature was 4 degrees Celsius. So do I have a go myself or do I chuck it into a garrage?
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »

Testing the CAN Bus.
As far as I know the Lexia can not test the CAN Bus directly it will only report failures flagged by the various ECU's.. I have never seen on my own car any of the messages you quote, as the Lexia when reading diagnostic codes is looking at stored messages in the respective ECU's one has to assume that something related to the CAN Bus caused them to be set. which could be one of the ECU's connected to it or the CAN bus wiring, If the CAN bus was totally U/S then the engine wouldn't even start so it has to be intermittent.

THe CAN Bus connects the Engine ECU Gearbox ECU the COMM 2000 unit on the steering wheel (Wheel position, cruise control ) and the ABS ECU, the fact that you don't have any errors flagged from the ABS might be significant in that it presumably is not seeing a problem with CAN Bus data..

The CAN bus actually uses two wires for data and it's design is such that it is supposed to be fault tolerant in the sense that most of the data will get through most of the time if one of the data wires is compromised. One thing that you could do using the parameter check mode of the Lexia is to choose a parameter that goes over the CAN bus e.g. Torque (but there are others) and record the data while driving, what you would be looking for are step changes e.g big changes of data value for which there is not a logical explanation. The. engine ECU calculates a value for Torque which it sends to the gearbox ECU so that the gearbox can calculate gears, Torque converter lock up etc
The other thing that can be done to test the CAN bus is to use an oscilloscope to look at the quality of signal this requires finding an access point, I don't know of one, if I was doing it I would probably identify the wires carrying the signal and at a convenient point insert two thin needles through the insulation so that I could connect the signals to the scope.

If you really want a document that will tell you all you need to know about CAN bus and data comms send me an e-mail address that will take large files.

Injectors checking.
The engine ECU calculates the amount of fuel that needs to go through the injectors it does this to a high level of accuracy, the only assumption it makes is the conductance of the injector, it is an assumption because it cannot measure it.
Injectors are calibrated on the bench as a set, however there are small variations in the calibration and it is for this reason that there are configurable parameters in the ECU to program the "injector class" which as I understand it is another way of saying injector conductance. The upshot of this is that if the wheel size is correct yet there is a significant difference between the computed MPG and the value calculated by means of tracking fuel used by noting what goes into the tank the ONLY thing that can cause this is that the injectors are passing more (or less fuel) than the ECU computations allow. for. (The mileage term in both calculations is derived from the same source). I emphasise that contrary to many statements the ECU calculations as displayed on the instrument panel are very accurate if the injectors are good.
As far as I know the only way injectors can be calibrated is on the bench as a set.

Anyway reading back you have already proved that the indication is substantially correct so I don't think you have an injector problem.:-)

Brakes
The rears don't do a lot of work so 45 degrees probably represents some degree of binding. Taking them apart can be difficult, depends on the amount of corrosion in the long bolts holding the calipers together, if you have a garage that you know will do a good job, maybe the way to go but doing it yourself you can be sure that it is put together in such a way that corrosion won't be a problem in the future, believe that this has been covered on here at least once so a search on the forum might be worth while.
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Paul-R
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by Paul-R »

Interesting post Tony
cachaciero wrote:...the ONLY thing that can cause this is that the injectors are passing more (or less fuel) than the ECU computations allow. for.
Is the amount passed what is injected into the engine or what is delivered to the injector? I.E., could excessive leak off back to the fuel tank cause an MPG error?
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Sloppysod
I've elected to get the rear brakes fettled up and serviced courtesy of a garage my brother recommends. As my brother is in the car parts business he'll supply discs and pads as well which they can fit as necessary.

Cachaciero
This morning as I was reversing out of my parking spot the car threw a "Gearbox Fault" error on the dashboard display. All drive was lost. Turning the engine off and restarting a couple of times cleared the fault and I was left with no excuse not to go to work. I suspect this could be a CAN bus issue. I suppose I could put it into an auto electrician to have it fixed as presumably he will have the kit and experience to track the problem down.
I shall put the car on the lexia this evening and see what new faults have appeared.

I'll let you both know how I get on.

Many thanks

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

Post by cachaciero »

Paul-R wrote:Interesting post Tony

Is the amount passed what is injected into the engine or what is delivered to the injector? I.E., could excessive leak off back to the fuel tank cause an MPG error?
I have never had an injector test bench to "play " with so to some extent what I am about to say is a guess :-)
. A perfect injector will not have any internal leaks but a "real life" injector does have some level of internal leakage even when new. My guess is that when calibrating an injector the fuel pressure applied would be a constant then when "fired" the amount of fuel that actually passes through the injector to the "combustion space" is measured, as is the amount of leak back, higher leak back obviously goes in step with less fuel going into the " combustion space" . There will be acceptable limits for both of these quantities and from these numbers a calibration value which reflects the amount going into the cylinder is calculated, this number is quoted as a "class" which value is programmed into the ECU when doing an injector change. Note it is possible that there are several different "classes" for the same injector type but the ECU only accepts one value which is why injectors need to be a matched "class"
From this I would expect that any changes to the injector calibration i.e increased internal leakage would cause MPG errors.
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by cachaciero »


Cachaciero
This morning as I was reversing out of my parking spot the car threw a "Gearbox Fault" error on the dashboard display. All drive was lost. Turning the engine off and restarting a couple of times cleared the fault and I was left with no excuse not to go to work. I suspect this could be a CAN bus issue. I suppose I could put it into an auto electrician to have it fixed as presumably he will have the kit and experience to track the problem down.
I shall put the car on the lexia this evening and see what new faults have appeared.

I'll let you both know how I get on.

Many thanks

Donald.
A list of faults would be interesting, would suggest that you leave the Lexia connected and set up so that you can interrogate the system when problems happen because there are some errors that get set but then get cleared if the system subsequently works normally.
Auto electrician??? well if you can find a good one with the kit and a good knowledge how to use it.The problem for all / most independents is getting the detailed technical info required to understand how a system should work, something you really need to troubleshoot at more than a superficial level.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Well I've checked the fault logs, there are two new ones in addition to the faults already posted:-

ABS - Temporary Fault No communication with auto gearbox ECU data invalid

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

..and one change of a fault to intermittent status

GEARBOX - Intermittent Fault Multifunction switch coherence

So it looks like the Gearbox ECU is struggling to get its message across. Does anybody know where this ECU lives and how to get at it? I think I should check the connectors are clean etc at least. My brother has found me an independent auto electrician who is well versed in CAN bus diagnosis and Citroens so if I don't get anywhere I'll probably let him have a go. As for the brakes I'll get those sorted next week some time.

Thanks for all the good stuff!

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

Post by cachaciero »

Well the ABS warning is consistent and tends to confirm that data is not being sent from the gearbox ECU rather than failure of the CAN bus itself. Bear in mind that no communication may just mean that the data packets / message is unintelligible not necessarily that it not receiving messages.

On the Mk1 the ECU is on the RH side looking in from the front together with the Engine relay unit and the Injection ECU .
Not sure what the multifunction switch coherence refers too BUT the gear selector operates a multipole / function switch on the gearbox the data from this switch is routed to the Gearbox ECU the kicker is that in M mode the up /down switches are in the gear change lever assembly itself and are routed directly to the Gearbox ECU now if the gearbox switch was not in M but the lever was, then a manual up / down change would probably be a bit confusing for the system even incoherent :-)..However it could be that something in the box electrovalve position for example does not agree with the selector position.

Would agree that checking / reseating the ECU connectors is a good move but also get to learn howto use the Lexia to monitor gearbox parameters, I am sure that one parameter is gearbox selection inputs and demanded torque would be another parameter worth looking at. The gearbox looks at the accelerator pedal position (from the engine ECU via the CAN) then using road speed obtained from the ABS ECU (via the CAN bus) input speed and current gear selection etc calculates a value of torque required from the engine and sends that to the Engine ECU (via the CAN bus) the engine ECU then calculates the required fuel to inject to achieve the demanded torque. As you can see many things come into play in this and in ways that that may not be immediately obvious.

With ref to my previous comments re CAN bus and diagnostic, found something today which shows that the CAN bus (buses) are available on the diag socket not sure at the mo how Lexia interacts with this or even if it can without an additional interface, quite possibly depends upon the Lexia device and firmware on it.
skycat61
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Re: C5 2.2 HDi 136 Facelift - poor MPG and no bottom end grunt

Post by skycat61 »

Thanks Cachaciero, I shall have a go at the connectors this weekend. Regarding the multi function switch on the gearbox I found this online:-
http://www.peugeotlogic.com/workshop/ws ... switch.htm which suggests it is a common problem with the switch itself. On Ebay there are genuine switches for about £80 from Russia, and cheaper "no-brand" ones too.

I have yet to figure out how to get the lexia to monitor and record gearbox functions/performance. Any help with this would be much appreciated.

Also if the CAN bus is brought out to the diagnostic socket that would facilitate checking it with an oscilloscope. Again I've been trawling the web and there are good descriptions of the operation of the two wire bus.

By the way, it threw the same "Gearbox Fault" and "Speed Control Fault" this morning while I was reversing out in exactly the same way as before. Turning the ignition on and off twice again cleared the problem.

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

Post by RichardW »

That sort of random shennanigans often results from a failing underbonnet fuse box. However, are there any EGR valve error codes stored? These can set all sorts of other faults that are seemingly random!