Norwegian 1.6hdi C5 with weird engine sound!?

[Axa]

Hello. I live in Hemsedal, one of the largest ski resorts in the Norwegian mountains.
I have been driving a 2006 C5 break for almost 5years now.
Have had the common "Depolution system faulty" error coming a few times a year.
Had a melted wastegave vacuum tube. Rusted trailing arm bearings. (filled up New ones with propshaft grease. Expect them to last forever now!)
Things that are common C5 issues. And reasonably easy fixes.

But Now I'm really worried!
On idle, the engine makes a very low "thumping" sound. And sometimes a high "cricket" like sound.
I guess it got the 1/4 of the engine revolutions. Have not managed to count that so far because the sound comes and goes.
A mechanic suggested it migh be a valve that is not closing properly on idle. The sound goes away as the revs goes up.

I can't localize where it comes from more then that it appears to com from the rear of the engine compartment.
It's sounds louder with the lid closed.

I will have the timingbelt and waterpump changed in a few week's as the mileage just paste 200,000km.
I would really like to fine out what causes this worrying sound as soon as possible!

Any suggestions?

Best regards, Gunnar


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[myglaren]

Welcome Gunnar

I've moved your post to the Citroen forum as it is more a question than an introduction.*

You don't say which engine you have, or the model spec, which can make a difference in some cases.

I've had the 'cricket' sound on both mine (2L HDi) and it was a seized alternator pulley, that in the current car took the serpentine belt pulley with it.

When changing the timing belt and water pump, be prepared to change any and all tensioners and idlers.

Can't imagine what the thumping sound might be other than perhaps a deteriorating engine or gearbox mount.

*ED: then of course spotted your other pos

[Lighty]

The 1.6 hdi engines suffer from noisy cambelts, this would normally fit your cricket description. We change many due to,this noise rather than any other reason.
The cam chain can also become noisy, but it is hard to say from your description.
Main point of my post is to warn you not to rotate the engine backwards at any point when fitting the belt, the results can be disastrous .

[Axa]

The "low thumping" sound is now cured. I removed the inletmanifold and found it filled with a layer of goey carbon contamination. After cleaning the manifold, and as good and far down in the inlets as possible I started up and found out that one inletvalve was not closing all the time on idle.
I solved it by spraying some diesel, wd40, bbq cleaner down the inlets. Before a final spray with bike chain lube I used a gasburner to burn out contaminations while the engine was running. Now all valves are sealing again.
I have also cleaned out the DPF and catalytic filter with highpressure washer. And also blanked of the main cause, the ERG valve. :@

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[Lighty]

Good call, they tend to look like this