C5 2 litre Hdi power loss -still not resolved.

[myglaren]

Easy enough to take the MAF out of the air circuit just unclip the rubber pipe between it and the next plastic bit, o.k so you run without air cleaner but that's o.k to prove the point.

cachaciero

Or disconnect the plug to the MAF.

Boris. I expect both open and short to be fault states - it is probably expecting a pulsed signal and in the absence of such a signal can't determine the exact fault.

[cachaciero]

Logic and painstaking and detailed measurement is a requirement for sorting things on these cars.

It is no good taking a gash MAF lying around in the corner of the garage and fitting that unless you know with absolute certainty that it is a good component. We also know from other posts that blocking the EGR can also cause Warnings and LIMP mode so blocking the EGR is not a positive diagnostic technique.

Back to your problem you / we know that the Lexia is saying Airflow and you have the Warning Light on.

Your description of performance is consistent with lack of boost pressure. Could also be consistent with a MAF failure and or EGR failure so we need to try and eliminate one or the other.

We should also bear in mind that we may be looking for more than one defect.

First using a vacuum gauge check the vacuum level, vacuum is used for actuating a lot / most stuff around the engine inadequate vacuum could be responsible for many things not working correctly, the vac should be in the region of 200 mB absolute, anything much higher than this and the vac system should be checked for leaks.

Using the Lexia parameters you can read in real time both boost pressure and air flow are these figures consistent with what you would expect under a given set of driving conditions? Does the boost pressure indicated by the Lexia agree with a pressure gauge taped into the manifold?
Air flow calibration is harder to check but there is one thing that you can check that is air temp, is the actual air temp using a thermometer adjacent to the air inlet the same as that indicated on the Lexia a difference could indicate a MAF failure.

Does / can anybody on here with a good 2.0 Ltr and a Lexia record values of air flow at 1000 rpm intervals to 4000 revs and air temp that would be a useful table to check MAF's against.

As previously suggested take the MAF out of the air circuit and note the difference if any, no difference is a strong indicator in your case that the MAF is not well.

Go do these things and then come back and tell us what the results are.

cachaciero

[cachaciero]

Easy enough to take the MAF out of the air circuit just unclip the rubber pipe between it and the next plastic bit, o.k so you run without air cleaner but that's o.k to prove the point.

cachaciero

Or disconnect the plug to the MAF.

Which with respect if you had read my previous post is precisely what we are trying to avoid, disconnect the MAF and the ECU will post an error and likely put the engine into LIMP mode and do none of the calcs related to the MAF which is not what is needed.

cachaciero

[myglaren]

True enough!

I imagined that a failed MAF=a disconnected MAF.

The electronics guy that I gave my dead one to seemed to think that a failed thermistor would be the most probable fault as the platinum wires were virtually indestructible.

When you clean them with a cotton wool bud they're not

[boristhespie]

Has the new maf sorted things out for you?

Do new mafs need programming when fitted.

Re vacumn. Reading it all I just think its beyond me. Don't have testing equip. Need to get haynes to name the bits for me. Ebay methinks.

[myglaren]

Yes! And how!

The improvement was quite dramatic, pulls exceedingly well from a standing start, boosts from around 1300 revs now as it should. Will squeal the tyres easily and the tyres are new Yokohamas.

Goes very well at motorway speeds but could do with a little extra kick there.

Still needs a pair of injectors and a MAP. Slow to start which will be the injectors no doubt.

[Clogzz]

Tasmania ... 2006 C5 TDi … disconnected the throttle cleaned all the contacts

Welcome to our nightmares, 3CV !

Diesels don't have throttles and the 2006 C5 has a Hall Effect pedal sensor with magnets where nothing looks like it may go wrong.
Your fault looks like loss of fuel pressure.

[cachaciero]

True enough!

I imagined that a failed MAF=a disconnected MAF.

The electronics guy that I gave my dead one to seemed to think that a failed thermistor would be the most probable fault as the platinum wires were virtually indestructible.

When you clean them with a cotton wool bud they're not

A disconnected MAF = a failed MAF
A failed MAF does not in electrical terms equate to a disconnected MAF

I believe a MAF has two thermistors one to measure air temp and a heated one that also measures air temp the difference being that the the resistance of the heated one will be proportional to the air flowing over it, from a comparison of the two mass flow can be calculated. If the MAF only consisted of these two elements then on the bench resistance checks of the thermistors would produce results that could be interpreted as go no go.
However I think that within the sensor there is more than thermistors like an amplifier and maybe a constant power source for the thermistor heating.

Platinum connections well I don't know different, but I am surprised platinum being expensive and gold plated wire being adequately corrosion resistant for the application really I would have thought even stainless wire could be used if strength and corrosion resistance were the main criteria. ..... Must do some more research

cachaciero

[myglaren]

It is the platinum wires that measure the airflow - they are heated and apparently in a Wheatstone bridge configuration.

The thermistor measures the absolute temperature while the platinum wires measure the airflow by calculating the amount of current required to maintain their temperature, and thereby the airflow.

[3CV]

Thanks Steve for that.
I have been looking at all possibilities and did what perhaps I should have done first, which was to disconnect the battery. Once reconnected the problem appeared to be rectified but I wasn't brave enough to drive it further than my gate as I use a wheelchair and it was p^##ing down with rain. I'll try again in the morning before taking it back in to the repairer as presumably there is still something wrong with the EMS, on-board computer or possibly something else?

[cachaciero]

It is the platinum wires that measure the airflow - they are heated and apparently in a Wheatstone bridge configuration.

The thermistor measures the absolute temperature while the platinum wires measure the airflow by calculating the amount of current required to maintain their temperature, and thereby the airflow.

Ah...! that makes sense.
Went away and did some reading on hot wire sensors, two things struck me. Dirt and oil contamination will reduce it's accuracy and it requires a laminar flow across the sensor.
The implications and resolution of the first are relatively well understood but the implications of the second need a little thought a laminar flow can be quite easily upset both by upstream and downstream events, not sure how relevant that may be but needs thinking about.
Incidentally the text I read was critical of using carb cleaner to clean the sensor suggested that an electronic component /pcb type cleaner would be better.
It also mentions that some hotwire devices have a contamination burn of cycle that applies high current for a second or two on engine switch off to burn of contaminates, don't know if the Bosch / Siemans device does this but it does occur to me that burning oil off could leave carbon deposits if not hot enough.

cachaciero

[myglaren]

I too have read that contaminants can negatively influence the response of the heated wires but that carb cleaner or as you suggest electronic contact cleaner can improve operation.

Someone here cleaned theirs successfully with cellulose thinners.

[centurus2400]

Over the weekend I took the MAF out and gave it a good squirt with carburetter cleaner. Not that it seemed dirty in the first place, but I had nothing to loose. Replace, road test, no difference, no performance!

Next step, rather than unplugging the thing, was to disconnect the air inlet pipe from the back of the MAF, which took all of 30 seconds. This meant the car was just drawing fresh air straight into the turbo. Repeat road test and WOW! Performance almost back to normal, there was a huge improvement.

When the pipe was reconnected, the fault returned. As a double check I even temporarily removed the air filter from the box but that also made no difference.

Based on this I've ordered a new OEM MAF which should be here by the end of the week, and I'll report back when it's fitted. Though my car has a Bosch fuel system the MAF is actually made by Siemens.

Interestingly on the way to work this morning the MIL and antipollution warning came up so perhaps the MAF readings are now so far out of expected range that the ECU has at last noticed.

It's been an interesting learning experience, but given the initial symptoms it would have been so easy to start tearing into the turbo system when in actual fact it had nothing to do with the problem.

Like I said, these HDis can be tricky things.....but thanks to the FCF it looks like we've nailed this one

[citroenxm]

Id like to add a slightly different experiance but on a Xantia HDi 110.

I bought one in with the needing of a turbo. The car started and ran.. but no boost, you could see the intercooler pipe being sucked together from the engine when revving the engine.

Anyway, I fitted another turbo from a known good engine and to my surprise it STILL did the same! At first I thought the old turbo then had nothing wrong, however, the turbine was not smooth in operation.

Anyway, yesterday I decieded to try the small solinoid valves that sit by the cam belt cover (On Xantia HDi's, over by the Brake servo on C5's) and borrowed them off my car.. when suddenly Whoo hooo we had full boost pressure to 1500 milli bars.

The point I was going to make was I had been told if the solinoid valves got warm with the ignition on this indicated they worked, and thats what these were dooing. I put them on my own car, and the problem moved to my car.

So the point I was going to say was check the Solinoid valves for lack of operation. I dont actually know how to test them only by substituting them with working ones.

Paul

[cachaciero]

Nice one!
have to say that I never considered that taking the MAF out of the air circuit might actually give an improvement in performance.

Based upon my experience I was expecting it to be the same or worse, so when you get a new one the performance should be even better.

cachaciero