I suspect the EGR valve on the NC Astra is sticking, which sometimes causes rough running. I'm considering temporarily blanking the port from the exhaust to see if that gets rid of the problem, hence confirming the EGR valve as the culprit.
Are there any reasons why I should not do this? Can it cause any lasting harm to the engine?
Number_Cruncher
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There has been a thread on this before. My reply was that I believe it to be unwise, since the EGR valve is crucial to maintaining engine temperature. Without it the engine could get too hot and damage the turbo.
However, someone with more knowledge, particularly of the GM engine, may know better.
Where is Aprilia??
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There has been a thread on this before.
This one maybe?
www.honestjohn.co.uk/forum/post/index.htm?t=23298
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If it's operated by vacuum, you could just disconnect the vacuum pipe (or blank it with a ball bearing etc...) Might be worth getting a visual on the valve to make sure it isn't stuck open before you disable it.
There are lots of threads on other forums about disabling EGR on all manner of vehicles, the general census was that it was OK, all it does it reduce the peak flame temperature at certain throttle positions and loads to reduce NO2 emmissions, the combustion temperature was still greater under other conditions.
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Number Cruncher, Can't help with an Astra, but I've blanked off a few Transit 2.5 Di valves.
The symptoms were always the same, bad cold starting, poor cold idling and an acrid exhaust smell. Blanking the valve (metal blanking plate) always showed that the EGR valve was at fault. I used to run them for a few hundred miles to confirm the results, then replace the valve. Never had any long term problems !
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Well, I've got the blanking plate made up and ready to go. I'll fit it in place this weekend, and I'll report back any changes, good or bad!
Thank you all for your views and thoughts.
Number_Cruncher
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I wish that I had fitted this blanking plate earlier - it's a different car! It is more responsive, and although we don't keep spreadsheets, it seems to be using less fuel.
My concerns about the wisdom of making this modification had stopped me from implementing the blanking plate solution until a month ago. It was then that I learnt that in the newest release of engine management software for this engine, the EGR is disabled. Further to this, if the EGR valve is stuck open constantly, there is now a Vauxhall blanking gasket available to fit under a warranty code in Vauxhall dealers.
Number_Cruncher
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Blanking the EGR valve should slightly improve economy but increase NOX emissions;there should be no other effect.If it was stuck open it will certainly have a bad effect on the vehicle as it will recirculate exhaust when not needed-ie. idle and WOT.Overheat the turbo??the turbo only works hard at WOT(wide open throttle) and at WOT the EGR valve should be closed.It may,on very late vehicles,of all makes show up in the diagnostic codes,as most calibrations have overall electronic control of the valve tho' the the actual opening and shutting of it is done by vacuum.
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blanking the egr valve is the best thing that you can do for the engine.it is interesting to note that land rover actualy sell blanking plates as a land rover part
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The EGR valve is there to reduce pollution.
If you don't give a darn about the environment or other peoples health, why not go the whole hog and run a V8 on leaded petrol!
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RT, I don't need your sanctimony - there's enough of that on this site as it is.
As for emissions, I'm sure that all the unburnt fuel swilling through the cat was doing the emissions a world of good when the valve played up.
The car was already on its second new EGR valve during my ownership - I had tried to 'do the right thing', but that wasn't successful.
I thought long and hard before making this modification, and I certainly haven't got a lax attitude towards the environment.
Number_Cruncher
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Oh dear...and what about the pollution and energy and materials needed to make a new EGR valve, all that mining, extraction, smelting, casting, transporting etc....? Far more than the poxy bit of laughing gas the car will give off.
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worst thing ever invented EGR
cause more polution...........than what? a hot air balloon?
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It reduces NOX but by lowering the efficiency of an engine,it increases CO2.
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I would still be concerned about the long term consequences of removing the EGR valve in a turbo engine. The engine must run hotter.
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50% of the code in an ECU is redundant. While the computer does use the information from the valve to refine its thermal model of the engine, if it's closed off it'll fail over to a standard model.
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Please explain why it must run hotter.If you improve an engine's efficiency,then you don't need to open the throttle so much to get the same performance.
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"Please explain why it must run hotter.If you improve an engine's efficiency,then you don't need to open the throttle so much to get the same performance."
My understanding is the nox is also used to stabilise temperature. However if you're running at part throttle because the engine's efficience is greater, then you are probably right. About three years ago I was in a lengthy 'debate' about this to a mechanic concerning an Espace 2.2 dCi. However I am ready to stand corrected...
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Although I don't have the full power of knowledge of chemical rate kinetics to inform my view, here's my understanding of the interaction between EGR and NOx.
At higher temperatures, the 'combustion' of Nitrogen to give NOx is possible, owing to dissociation. This is a reversible reaction, and the amount of NOx is dependent upon the amount of the free radicals required.
When the temperature of the combusting gases falls below a critical temperature, the reverse path of the reaction from NOx -> Nitrogen and Oxygen becomes impossible, so the amount of NOx becomes 'frozen'.
EGR dilutes the charge, and, as such, reduces the *peak* combustion temperature, thus reducing the opportunity for NOx to form.
I don't think that removing EGR will put significant extra thermal stress on engine parts because the peak temperature only occurs within the volume of the combustion gas, and is effectively quenched by the relatively cold surfaces of the in-cylinder parts.
Number_Cruncher
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'The EGR valve is there to reduce pollution.'
That's when they work properly-which they don't.If ,years ago ,it had been suggested that feeding exhaust fumes into the engine was a good idea,people would have fallen about.
Incidentally,my car has a carburetter,I would love to put a v8 in it.Leaded petrol is no longer available.
The real polluter is building new cars,not what comes out of the exhaust.Now they are so designed that they will be beyond economic repair after 10 years look out for scrapyards full of shiny rust free cars and more pollution.
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EGR valves were first used in the US back in the sixties mainly on gasoline engines and have been used on gasoline engines in Europe in the Seventies/eighties.However electronic engine control has wiped out the need for them on gasoline because the accurate control of spark/fuel aids combustion.The exhaust coming out of a diesel is recirculated to reduce the amount of air(21% of which is O2)which goes in to the engine.This reduction of O2 reduces the combustion temperature which reduces the formation of NOX.These temperatures are well below critical limits so there will be no problems.Many European manufacturers nmarket the same engines with and without EGR depending on which country they will be sold into.Also some passenger vehicles had EGR fitted while the same basic engine in a commercial vehicle did not have it fitted due to a lower legal requirement.
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Leaded petrol is still available;four petrol stations within 20 miles of my house still sell it.Go to the Bayfordthrust website for your nearest stockist.
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www.leadedpetrol.co.uk is the Bayfordthust website.
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