C5 1.6 Hdi Top Engine speed is limited - erratic at high rpm

[NutsAndBolts]

Vehicle: C5 1.6 HDi 16V 110hp VTX Plus Euro 4 FAP
Mileage: 120’000 approx
I have had the following problem with this vehicle for over 2 years: The engine speed is limited and will not exceed 3800-4000 rpm when stationary (out of gear) and will not exceed 3500rpm when under load regardless of selected gear. At this rpm the engine seems to back fire - i.e. the engine jerks and and becomes erratic (like when an engine red lines). It also will not maintain a steady speed under load at 1500rpm regardless of the selected gear - the car jerks and judders though not as violently as at 3500 rpm. Two different Citroen garages have run diagnostics which have not shown any faults. The ECU, EGR valve, crankshaft sensor, and MAP sensor have all been change with no effect. The car has been has also been fully serviced. I am reluctant to spend any more money at the Citroen garages without a list of possible causes. Does anyone have any ideas what it could be or have any ideas of test that could be done to further pinpoint the issue? Thanks in advance for your help.

[citroenxm]

Any loss of oil from the engine? Has the oil level been dropping but no signs of leaking?

Lack of revs indicates possible blocking of intercooler with oil from prehaps a popped turbo..

[NutsAndBolts]

I haven't noticed any drop in the oil level. Also, the problem occurs when the engine is cold. Just turn on the ignition and put your foot down and it won't rev beyond around 3800 rpm at which point the engine speed is erratic. So its unlikely to be the intercooler I think?

Do you think its worth/possible to disconnect the turbo and see what happens when the engine run at high rpm?

[citroenxm]

Pop your turbo outlet pipe off.. and check the turbo shaft is free to rotate and not stiff..

[sparksie]

Also, change the fuel filter and make sure it's correctly sealed.
If the problem was air related I'd expect to be hearing about black smoke, so I think this'll turn out to be a fuelling issue.

[citroenxm]

Hmmm yes possibly. But thats useualy when the air flow has measured in air and then its escaped and less air gets to the cylinder then measured .. The ecu injects the air measured for whats flowed but ends up having to much fuel to air.

when my sisters intercooler blocked with oil from a buggered turbo it didnt smoke just lacked revs because it couldnt get any.. but the ecu measured a low air flow too so it didnt put too much fuel in..

I hope it is fuel and 1.6 fuel filters do block easy.. but useually cause a cut out problem when hard accellerating

[RichardW]

Has the cambelt been changed? Our 1.6 HDi runs much better since it was done, even though it was only 75k - albeit it was pretty noisy!

[Mandrake]

Good idea Richard - if none of the other suggestions prove to be the problem it would be worth taking the timing covers off and pinning the pulleys to see if the timing is wrong. (And if the belt is due, just do the belt and pulleys while its apart)

Maybe the belt has jumped a tooth or has been replaced and not timed properly. A tooth out would be enough to cause major performance problems but may not trigger any fault codes...

[NutsAndBolts]

Thanks for the expert input guys. You would think the problem has to be fuel or airflow related but its hard to pinpoint the cause. Just to update: The fuel filter, cambelt and waterpump have all been changed since the problem started so I don't think these are related. I will take a look at the turbo this weekend as suggested - but am still interested to hear any other theories and things to check for. Thanks again.

[NutsAndBolts]

I couldn't get the turbo outlet pipe off as it needs a special torx allen key tool to fit into an awkward position. I got the turbo inlet pipe off and I could turn the spindle with the turbo fan blades on using my fingers - It turns fairly easily but it doesn't keep spinning under its own momentum. Also I ran the engine and could see it spinning.

The turbo outlet pipe splits into two pipes. One goes into the inlet manifold, and the other to some where else which i'm not quite sure. I took "the other" pipe off and ran the engine and you could feel that the turbo was pushing a lot of air through - which I guess means the turbo is working. When it reach 3800 rpm I got the same problem. Any more ideas please? Thanks in advance for your help.

[citroenxm]

Well if the turbo turns nice and freely it sounds like its ok then..

Im out then. Not experianced this problem except intercooler full of oil..

Sorry.

[RichardW]

Think you need to get it on A lexia and check the pressure drop across the dpf. It should be less than 50mbar at 3k rpm. I would also check that the boost actuator on the turbo is free to operate - it should be easy to push down and spring back almost instantly.

[NutsAndBolts]

Thanks Richard. I have a Lexia and have checked the pressure drop at 3000rpm as suggested. The Particle filter inlet / outlet pressure difference is 58.8 millibars so a little higher than you say it should be. Do you think this could be it? Maybe I should run a Forced regeneration cycle? Full output below.

Parameter measurements : EDC16C34_DV6
Name of saved screen
Particle filter information
Engine speed
3084 rpm
vehicle speed
0 kph
Particle filter soot load
18 %
Average distance between regenerations over the last 5 cycles
411 Km
Distance travelled since last regeneration
103 Km
Weight of additive in the particulate filter
34 g
Amount of additive remaining in the tank
1872 ml
Cat. converter downstream temperature
127.1 °C °C
Particle filter inlet / outlet pressure difference
58.8 millibars
Air manifold temperature
52 °C
Flowmeter air temperature
42 °C
Coolant temperature
76 °C
Injected flow measured
7.84 mg/cp
Inlet air heater throttle opening control (If present)
-0 %
Additive system fault
Additive addition impossible
Air volume flow
173 Kg/h

I

[NutsAndBolts]

This turned out to be a small leak in the vacuum pipe which controls the turbo.
Hope this helps.