C5 Turbo at too high pressure

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bencowell
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C5 Turbo at too high pressure

Post by bencowell »

My C5 2.0 HDI 110 has always driven perfectly. In the last month however, the car has been feeling short of power.

Most of the time the car has been a bit slow to accelerate, and it was almost impossible to accelerate up motorway hills.

Every so often the car would "cough", followed by a cloud of black smoke and an abundance of power (how it should be).

After coughing, the car would feel great for a varying amount of time. The car usually performed better before the water reached normal temperature. The oil reaches "urban" temperature a few miles later. (C5's have oil and water temp guages).

I initially thought it was an EGR or MAF problem, hopefully more likely the former, but my main dealer says it is the turbo operating at too high pressure. I queried this saying isnt there a valve to release pressure. He said yes, but thats whats broken and isnt available seperately.

There has been a whining noise on over-run, best heard when stationary with the bonnet open, the noise has existed for a year and was queried twice while in warranty. The dealer has not yet asked Citroen about a goodwill payment (5 1/2 months out of warranty).

If a turbo is producing too high a pressure, what is the outcome of long term use? Would a rubber hose pop off before the engine self destructs? Could it cause any long term damamge to the engine?

Does this sound reasonable to anyone? I intend to get a second opinion before spending large amounts.

Thanks in advance
Ben
Rostami
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Post by Rostami »

Hi!
I am not a Turbo expert, and indeed it is not a simple topic.

Turbos can have two flavours: Either they are effcicient at low RPMs or they are efficient at high RPMs.

Low eorking RPM turbos are best for small engines, such as the case for automotive, and to relief the turbo when the engine runs faster, there is the dump valve to bypass exaust gases / power from the turbo.

How does your car feel at low RPMs? Is the dump-valve working correctly?
On the HDi engines, the EGR is only used in a limited RPM range, so it is important to understand under which engine RPM you have problems!
Xantia Activa 2.0 HDi (1999)
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bencowell
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Post by bencowell »

The car feels pretty much the same at low throttle low (sub 2k) revs.

The coughing appears around 2000-2500 rpm. When this happens the power appears straight away.

Motorway economy appears to be around 7 mpg down. Town economy is similar, maybe a couple of mpg lower. I have owned the car for nearly 3 years and done 44k (50k on clock) and have always got 43 mpg plus, rising to 50 at 70mph on clear motorway using cruise control.

Together with the being worse at higher temperatures I assumed it was an EGR fault.

Ben
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Post by Peter.N. »

All my experience so far has been with mechanically controled injection systems and with those an increase of turbo pressure would equate to an increase in power output as the increased pressure would result in increased fueling via the pressure sensor on the pump. I suspect that the elecronic systems works differently, with maybe a over pressure sensor shutting the fueling down, if this is the case, I think it has to be down to an electronic fault, probably a sensor or a sticking turbo wastegate. The black smoke is the only thing that puzzles me, I suppose you dont have a very large build up of soot in the inlet manifold from the EGR, sufficient to obstruct the air intake?
bencowell
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Post by bencowell »

I was looking earlier and the EGR on the C5 looks easy to get at. I was considering removing it, but need to know first if you need a replacement gasket or anything, or if bolts are going to rust solid (like anything on an exhaust does). Seeing as Mr Citroen will probably be looking again I shouldn't mess with things.

Dads Picasso 2.0 HDI 90 had an EGR problem that gave similar symptoms.

Thanks to everyone so far... the story will no doubt continue.

Ben
pugxpert
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Post by pugxpert »

your turbo has a solenoid controlling the wastegate via vacuum,on intercooler or somewhere near there will be a turbo pressure sensor,the ecu in its map at a given rpm and engine load will require a certain turbo pressure say 1600mb it reads this on the sensor then controlls the solenoid valve to move wastegate and obtain the desired pressure measured at sensor,closed loop system,this all happens very quickly.your car will record a fault if it sees turbo pressure too high or too low by 400mb for 10 seconds.you could have a fault with turbo solenoid valve which controlls vacuum,307/406 suffer with these, or your turbo pressure sensor is telling ecu duff information,your waste gate capsule on turbo could be sticking had this on 607.hdi 90 has no pressure sensor turbo controll is done in the normal way with wastegate/capsule on turbo.110 and 136 have this vacuum controll system.these solenoid valves take there vacuum from the same source so if one fails and dumps all the vacuum will effect egr as no vacuum left.hope of some help....
EP6T petrol turbo nice engine in the 207 GT and the new mini....
bencowell
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Post by bencowell »

So.....

A vacuum problem can affect turbo boost pressures (Performance)

A vacuum problem can affect the EGR (Black smoke, Performance)

and the brake pedal sinks when you pump the pedal a few times and keep pressing it hard. Could this be vacuum related too?

Is the noise you hear on overrun (when stationery) vacuum related?

I think it needs a turbo/bosch diesel specialist to look at it in addition to the Cit garage.

If anyone has any more suggestions....
pugxpert
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Post by pugxpert »

the noise heard on over run when standing still could be the alternator,they have a free wheel built in pulley so engine slows down and alternator keeps spining makes a whining noise.a bosch agent will check the fuel side of your car but not the turbo ,if you can get hold of a vacuum gauge i would drive it with that 't'ed into the circuit then drive and see what happens
EP6T petrol turbo nice engine in the 207 GT and the new mini....
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