Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: mark.adams on 03 March 2008, 09:05:52
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What does it do? I've heard that you can blank it off and it makes no difference so why is it there??
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recircualtes some exhaust gasses...
Mine stated leaking (evidence of carbon deposits down the side of it)
was causing car to idle erratically, and report IACV and MAF errors incorrectly.
Popped it off, using the gasket as a template, cut around a bit of coke can, reassemble, gasket, can, egr. jobs a good un
Issues fixed, and possible ever so slightly more economical.
It's purpose was to reduce emissons in a stricter market I think
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EGR - Exhaust Gas Re-circulation
What this does is allow some of the exhauts gases to enter the inlet track.
Why, you may ask.
Well, exhaust gases can be considered inert (in the combustion engine perspective) on a properly functioning engine as they (should) contain no oxygen or fuel as it will have all been burnt.
So, what the ECU does under certian load/rpm conditions is allow some of the gases back into the inlet.
The effective of this is to lower the cylinder temperature by introducing a proportion of gas that wont burn. A lower cylinder temperature results in lower NOx emmisions and NOx is part of the approvals for new cars and important in certain countries/states (i.e. California). It is not however tested at the MOT!
In theory, there can be an additional benefit in the form of added fuel economy because with the EGR valve open, you need a slightly wider throttle opening which ups the volumetric efficiency of the engine (less restriction to inlet air etc). But, dont get to excited about this because on the Omega engines the EGR flow is very small so this doesn't realy apply, its only on some of the latest engines where high EGR flows are being used that this can realy be quantified.
Its also improtant to have an understanding of the operating conditions for the valve to as this helps with diag.
The valve will be fully open when cruising and fully closed on full throttle and idle. The latter is important because, if it was open at idle where the engine is not using much fuel/air, the dilution would be significant resulting in poor running and hence why we sometimes sudgest checking the EGR if poor idle symptoms exist follwing the basic checks.
Similarly on full throttle we dont want exhaust gases limiting power output!
Now, EGR is not used on all the Omega engines, the 2.6/3.2 for instance dont have it and this is mainly due to them running at a lower compression ratio. The down side of lower compression is lower power output and efficiency (Gm managed to recover this back on these engines by using a later fuel injection setup but, it would be interesting to know what they would be capable of with a compression ratio similar to that of the 2.5/3.0!)
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Thank you, a nice concise explanation there :)
I might consider blanking mine off then, that was the only code in my ecu when i had the codes read, normally happens if i switch off after using LPG and start on petrol, it takes a bit longer to start and the emissions light comes on but by flicking over to LPG again the light will go off.