After the replacement of the rocker cover gaskets on my(*) '94 3.0 Omega a few weeks ago, the idle, especially from cold has been noisy. The noise disappears when the engine is warm, though the idle is still not as ultra smooth as it used to be. It's been to various garages including DK cars at Thatcham (who I would throughly recommend), but has been difficult to pin point as the engine has been warm/hot when looked at.
On cold startup the noise has actually got worse over the last week or so (maybe due to the colder nights/mornings?) and it seems to be coming from the pipe connecting the EGR valve to the manifold. Again as soon as the engine has warmed up the noise disappears.
Is this a common problem and how much will it cost to rectify?
If it costs a packet, is this something that I can "ignore" without causing any damage to the engine?
Thanks.
(*) Don't ask how I obtained ownership of this motor which previously belonged to my mate/neighbour!!
Chad.R
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Noisey,
Very vague, please describe the noise and establish whether the engine is breathing a lot from the pipe when it is cold. The idle will nor be as smooth with this pipe disconnected or probably any other that you had removed when you change the gaskets. Did you have to remove any heavy deposits from the covers when they were off ?
Regards
Peter
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Peter,
I took it to a garage from the "HJ's good garage" list for the work - the gaskets and covers were replaced. I've subsequently taken it back for them to look at this problem but they can't seem to find a leak. As mentioned before the engine was hot though.
I checked this morning when starting up and the "noise" is quite difficult to describe - it's a pulsing noise coming from the EGR pipe to the manifold. Similar to excess steam escaping from a steam engine's valve but higher pitched and at a regular frequency.
It does seem as if the engine is breathing through this pipe when the engine is cold. The other pipes connected to the rear of the plenum(?) chamber have also been checked and OK'd too.
Chad.R
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From your description of the noise I suggest what you are hearing is the normal action of the air injection pump pumping extra air into the exhaust when the engine is cold.This speeds up the catalytic converter warm up and the process only continues for about 30 seconds I believe.The EGR system is another completely separate emission control device and does not operate when engine is cold.If this was leaking I don't think it would matter whether the engine was hot or cold and it would severely affect engine idle.
David Davies (Tune-Up Raglan)
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EGR is an emission control feature that operates when the engine is cold and at certain other times. Exhaust gases are vented back into the inlet manifold at times when the fuel/air mixture is fuel rich, such as when the engine is cold. This has the effect of reducing the peak combustion temperatures encountered under fuel rich conditions and this reduces production of NO2 (Nitrogen Oxide). The EGR recirculation valve is held open electrically and also opens under high torque + low rpm such as hard acceleration at low speed.
I know of this because the EGR valve on my Omega developed a fault and gave exactly the external symptoms of pinking (pre-ignition)- a metallic tinkling sound at engine speed when accelerating at low engine RPM - I knew that this could not be pinking and the nice Vauxhall man diagnosed it very quickly from a road test. Mine did not make any noise at idle but it is concievable that it could. Some later research reveals that if the EGR is stuck open, this causes a rough idle and/or stalling at low rpm. I would expect that a leak would be readily located by sound/feel, since the pipework on the exhaust side of the valve is at exhaust manifold pressure, or on the inlet side of the valve it is at inlet manifold pressure - either way it will blow or suck noticeably.
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I blocked mine off to stop such obnoxious gasses entering my inlet tract :)
My appologies to the trees!
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My feeling is that the leak is from the pipe connecting the EGR valve to the exhaust manifold - on the manifold end. When the car warms up the manifold expands and reduces the leak and the symptoms??? The noise seems to be coming from that general area too. Though without some sort of detection device it is hard to be 100% certain.
I appreciate what DD said about the air injection pump but this "problem" has only started since the repair. Previously once warmed up the car would idle rock solid at 500rpm on the tacho without the slightest flicker. From inside the car with the windows/doors closed it was very hard to tell if the engine was running or not due to the lack of noise and vibration.
Now the engine idles a couple of (tacho) needle's widths above 500rpm (probably around 550-575) and fluctuates gently between a needle width above and below that. The increased noise is as mentioned before, even if your deaf you can easily feel the increased vibration from inside the car. Every 10 seconds or so the idle will spike up to around 700rpm and then settle back in to the above pattern.
Many thanks for your time and effort.
Chad.R
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