EGR Valve operation

Diesel Do said:

Apparently not! That's how a petrol works. A diesel does not do that by design! It does not have any control of the amount of air going in so if it calculated it purely based on air flow you'd be flat out all the time!! Yes it uses the afm for injection but its only for correction and to keep em clean as data said! You are clearly not understanding me or what is written in rave!
A diesel engine is an air pump! When it spins it just draws as much air in as it possibly can this then goes out of the exhaust the speed is controlled only by the amount of fuel not air! So, there is always excess amounts of air!!! A set map controls basic fuelling for throttle position. Maf has minor influence. But the ecu knows how much air is needed for the amount of fuel it wants to inject. It uses the maf to modulate the EGR!!!!!! To add gas!!!!! But only enough to replace the spare air!!! So there is still enough for complete combustion as measured by the afm! If that level goes too low it reduces EGR! That's how it modulates it!!!!! It's not just open or closed. I've never said the fuelling is based on the amount of EGR! The furling is from a map. Air flow needed is from a map it's varied by EGR using the afm as a datum point.



Let's agree to disagree!

But you're wrong

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wammers said:

That is the entire point, the MAF controls fueling WHEN the EGR is working that is what it is there for. If there was no EGR you would not need a MAF.

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Datatek said:

As you pointed out and as it states in RAVE, the MAF controls fueling and the EGR. As others have said diesels with electronic injection control and no EGR also have a MAF as it permits finer control of fueling to meet emissions regs.

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6704nathan said:

wammers said:

The ECU adjusts fuel to match the clean air passing through the MAF. Why would you need a MAF on a non EGR diesel engine?

there are diesels out there with a maf and no egr
i can think of 1998 on nissan terrano tdi which have an air flow meter but has no egr or cat.
and also run like crap when it goes faulty. still say does more than control egr!

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wammers said:

They do which ones are those then?

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Diesel Do said:

Back to the beginning! You reckon an EGR valve poses no restriction?
Well, here's the one off my 04 Td5
View attachment 33989
Now I may be stoopid but that's one hell of a restriction. Remove it, improve air flow, more air flow, better response!

Its a slight improvement nothing to do with EGR not working it's good old fashioned airflow!!

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Datatek said:

Ok you found one well done. You may find the odd one, what you will not find is an EDC controlled EGR engine without a MAF. The MAF is needed to drive the EGR. EGR reduces engine performance, increases fuel usage and produces soot and particles in exchange for less NOx production. The ECU only injects fuel for the fresh air coming through the MAF. Otherwise you would get tremendous soot generation when the EGR is working. When people have gone to great lengths over many years, experimenting to get engines with maximum volumetric efficiency, for a so called mechanic to come on here and say there is always too much air in the engine is total bollocks. The maximum volumetric efficiency for a normally aspirated engine is around 137%. A turbo charged engine on boost can be well over 200%. More air, more fuel, more power. However combustion over a certain temperature creates NOx, so under certain conditions (Eg cold dense oxygen rich air) (that is why the air temp is measured as it comes through the MAF and not as inlet air temp as in the non EGR unit), exhaust gas is ingested via the EGR at certain times under certain running conditions to cool combustion, it does that by partially replacing oxygenated air with inert air, that reduces engine power. It also wastes about 3% fuel because the cooler combustion temp causes incomplete burn producing soot and particles. End of story, other than that believe what you want to.

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Datatek said:

I thought diesels always ran with excess air unless they are over fueling as there is no throttle?

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Datatek said:

I thought diesels always ran with excess air unless they are over fueling as there is no throttle?

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wammers said:

Bloody hell Keith can you stop this nonsense. Over fueling is too much fuel for the air charge. Over fueling cannot control the amount of air in the cylinder. You are talking silly.

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Diesel Do said:

Plus the ILT is an emissions control device that works with the EGR to make it more efficient by creating a depression in the manifold, not, to reduce air flow (which it does do) which allows better regulation of the excess O2 and therefore nox.

If there was no excess of O2 youd have complete combustion and not need EGR! That clearly isn't the case! In your version you remove air, remove fuel, add EGR, to make up the difference and reduce nox!!! That is wrong. It's spare air only that is replaced!! I admit that the system is far from perfect. But this is fundamental operational basics were talking about.

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Diesel Do said:

Sorry but you clearly are not reading what people are writing!

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wammers said:

Yeah i know how it works. The ILT valve restricts air flow greatly the EGR components of the valve restriction is neither here nor there. Some TD5s don't have the ILT valve fitted. Where does this spare air come from please tell?

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wammers said:

Oh i am reading it believe me, i just can't believe you can talk as much ****.

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Diesel Do said:

You sure about that?

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