Citroen C5 HDI Lack of Power and Banging

[wheeler]

I may be wrong, but I think the wastegate on these is normally closed and opens when vacuum is present, so a vac leak would tend to lead to too much boost rather than too little.

Only the 2.2 is set up to default to full boost without vaccum, the 2.0 90's & 110's have no boost without vaccum.

[cachaciero]

I may be wrong, but I think the wastegate on these is normally closed and opens when vacuum is present, so a vac leak would tend to lead to too much boost rather than too little.

Only the 2.2 is set up to default to full boost without vaccum, the 2.0 90's & 110's have no boost without vaccum.

Hi Wheeler

Not sure that that is really true. With no vac the gas path is reduced in area resulting in a higher pressure on the turbine but at the same time the turbine area is reduced. At low engine speeds this is fine the relatively low gas flow and higher pressure allows the turbine to boost more than it would otherwise have done. As engine revs rise the turbine pressure and flow rate will increase and there will be increased boost but not as much in absolute terms as there would be if the turbine was "wide open" i.e full vac on the actuator so I would guess that the absolute turbo pressure would be lower than it might otherwise be. (and there will be increased back pressure on the engine which means that it may not rev so freely).
However even like this there is more than enough boost to take it out of the ECU mapped boost regime and for the ECU to see it as overboost at some point under some conditions.
Turbo overboost is a common reason for engine managment lights ESP / ASR and pollution messages oftenl caused by a leak in the vacuum system and hence the turbo valve not working correctly or at all.

From my own experience my new to me C5 had a large vac leak because of a failed swirl valve diaphragm which meant that not only did the turbo actuator not work neither did the swirl valve. First stage was to isolate the swirl system from the vac supply which meant that the turbo system now worked correctly. I was gobbed smacked at the increase in performance which was solely down to the turbo working as it should.
So this tends to confirm my hypothesis that the turbo does not boost as much as it might with no vac over some parts of the rev band.

Cachaciero

[steelcityuk]

I think you really need to attend to the possibility that the crank pulley is faulty. If it is and it falls apart, it can lead to major engine damage. As others have said, bits of rubber can get behind the timing belt either causing it to fail or slip, in which case it will cause major top end damage. Examine the pulley for signs of failure. If there's no obvious signs, paint right across it with Tippex making a cross. Then keep examining the cross to see if the lines are moving 'out of step'. If they are it's failing. They usually make the most noise when starting or stopping the engine. The pulleys aren't cheap either.

If you lose vacuum on the old 2.0 HDi then you have no boost, I connected up a pipe to my C5s turbo so I could check the wastegate sometime last year, when I sucked on the pipe the turbo could be heard to spool up and boost even at idle.

The fact that your car only boosts at higher revs makes me think that you're looking at a sticking wastegate or faulty sensor/solenoid.

Hope you get it sorted.

Steve.

[boristhespie]

Okay, so the nise I methioned. I have just taken it tot eh Dundee dealer and he says the noise is coming from the powersteering pump. The belt on it is cracked a little (small cracks) and he is going to take it off and see if there is any play.

He also mentioned that the hydraulic pump was making noises. it soundede like a tractor for a sec when he pushed down on the car.

So the power steering pump.

Will be getting the lack of power looked into. There are a number of small issue now with the car which has been great up to now and these just seem like they are building to something more hence why I am asking a lot of things.

Any thoughts?