C5 2 litre Hdi power loss -still not resolved.

centurus2400 · Post by **centurus2400** » 06 Jun 2011, 08:58

I posted a while back about this problem which has developed with my 2001 2 litre Hdi.

Basically the engine seems to have very little boost pressure, though it starts and runs smoothly. Fuel economomy has also markedly improved, which leads me to think the engine management is responding correctly to the reduced amount of air going into the engine.

If I give it full throttle, particularly when going up a hill or otherwise working the engine hard, at about 3000/3500 rpm boost kicks in and the car will accelerate away normally - lift your foot off and let the revs drop and the boost disappears again, like turning off a switch.

The local indy has done a Lexia session and informed me that there are no fault codes showing and the live data readings are OK.

The vacuum actutator valve has been swapped with another secondhand one, and it made no difference. Disconnecting the MAF brings on the management light, and the power is even further reduced.

So where do I go from here...I had a hard job keeping up with a 2CV away from the lights last week

Post by **myglaren** » 06 Jun 2011, 11:05

Mine has exhibited similar symptoms for quite some time, sometimes they disappear - almost - then return with a vengeance.
There were fault code - lots of them on occasion and Paul (citroenxm) read and cleared them the read the live data that indicated two dud injectors, a faulty MAP and as I was already aware a ruined MAF.
Changed the MAF yesterday and the improvement is stunning.
It was much improved when Paul erased the stored codes but the faults gradually returned until MAF replacement.
The whole sorry tale, to date, is here but rather long winded unfortunately.

A couple of other forum members have also replaced a suspect MAF which was not throwing up any fault codes but experienced an immediate marked improvement to performance and economy.
They aren't cheap so it may be advisable to borrow a known good one for a test drive - it will be immediately clear if yours is faulty.

steelcityuk · Post by **steelcityuk** » 06 Jun 2011, 14:47

Stories of faulty and fake MAF sensors are out there, as myglaren says no fault codes but that doesn't mean they are working as they should.

Steve.

centurus2400 · Post by **centurus2400** » 06 Jun 2011, 14:51

That's very interesting, your fault s are similar to mine, though I don't seem to have any injector related problems - just as well really!

The main difference is that my MIL light never comes on and the performance is crap when the engine is cold, warm, or in between. The fault is always there.

I'm trying to avoid going down the 'replace expensive bits one at a time' route, though I guess it's always a possibility that the MAF is goosed after nearly 150,000 miles.

Oh for the good old days of the XUD.....

steelcityuk · Post by **steelcityuk** » 06 Jun 2011, 15:41

It sounds just like my Xantia was, under powered and economical. Never an engine management light on that either. The right place could diagnose it using Picoscope or similar but it's not a point and click thing like a Lexia session.

Steve.

boristhespie · Post by **boristhespie** » 06 Jun 2011, 22:20

Is a new maf about £80?

Post by **myglaren** » 07 Jun 2011, 06:51

£132.43

cachaciero · Post by **cachaciero** » 07 Jun 2011, 23:00

Have you checked for a stuck open or partialy open EGR valve?

cachaciero

centurus2400 · Post by **centurus2400** » 08 Jun 2011, 19:21

The EGR valve was blanked off some years ago

Starting to think I'm going to have to try another MAF despite the price. If it was giving a low reading it could certainly explain a lot....

Post by **myglaren** » 08 Jun 2011, 20:39

I was told of a procedure to eliminate the MAF.
Disconnect it and run the engine up to 5,00 rpm, hold it there for five minutes and it will be OK ever after. Supposedly worked on a scooby.

Not for me though. I'd rather pay the price than destroy the engine/turbo.

boristhespie · Post by **boristhespie** » 08 Jun 2011, 21:37

??? Not sure what you mean.

Also just got a quote for a new maf of £108 delivered.

They say it's a "genuine siemens", it that who makes it for Citroen and are these quality?

Post by **myglaren** » 08 Jun 2011, 21:44

Yes, mine is a Siemens but some systems are Bosch.

The idea was to bypass the MAF and revving the engine for five minutes supposedly 'taught' the ECU to ignore it.
Sounds like an urban myth to me.

centurus2400 · Post by **centurus2400** » 09 Jun 2011, 11:16

If I unplug the MAF it immediately brings on the MIL light and the dreaded 'antipollution fault' appears on the LCD screen.

The engine will run, but it's in limp home mode andt I assume the ECU has switched to some generic built in airflow values rather than measuring actual values.

I can't see that any car maker would bother fitting a MAf if it wasn't strictly necessary....

The system on my car is a Bosch, not a Siemens and up until now I have not had any trouble at all with it. Even the LP pump in the tank is the original one and still going strong

boristhespie · Post by **boristhespie** » 09 Jun 2011, 13:40

are the Bosch and Siemens interchangeable? Ie. Could I put a Siemens in if the one already in the car is a Bosch?

dnsey · Post by **dnsey** » 09 Jun 2011, 17:22

The engine will run, but it's in limp home mode

Quite, so how do you then run it up to 5000 rpm?
It's a bit like the old idea of catching a bird by putting salt on its tail.