wammers said:
It will spin quicker at all times when the EGR valve would normally be open. With the EGR open less exhaust gas is produced.
Click to expand...

Surely the excess oxygen/air that is in the cylinder is replaced with exhaust gas to lower the in-cylinder combustion temps and nox gasses so the volume of gas going into the cylinder is roughly the same just a different mix of gasses. There should still be the correct amount of oxygen to burn the injected fuel completely so the amount of gas coming out should be much the same just in different proportions depending on whether the valve was open or not! When the valve is open it'll bleed some gas away from the exhaust impeller possibly slowing it but I'd imagine that'll be minimal cos the turbo won't require the maximum amount of gas the engine can produce to spin!
 
Diesel Do said:
Surely the excess oxygen/air that is in the cylinder is replaced with exhaust gas to lower the in-cylinder combustion temps and nox gasses so the volume of gas going into the cylinder is roughly the same just a different mix of gasses. There should still be the correct amount of oxygen to burn the injected fuel completely so the amount of gas coming out should be much the same just in different proportions depending on whether the valve was open or not! When the valve is open it'll bleed some gas away from the exhaust impeller possibly slowing it but I'd imagine that'll be minimal cos the turbo won't require the maximum amount of gas the engine can produce to spin!
Click to expand...

Not as much oxygen, not as much fuel, not as much burn, not as much heat, not as much expansion, not as much gas.
 
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wammers said:
Not as much oxygen, not as much burn, not as much heat, not as much expansion, not as much gas.
Click to expand...

That happens when they stick open! If there wasn't as much burn it'd produce black smoke due to incomplete combustion of the injected fuel! EGR is only meant to replace the spare air. Which wouldn't affect expansion, it combines with nitrogen at high temps tho. A diesel doesn't regulate the amount of air like a petrol does. It always takes in as much as it can. So the excess air only is replaced! If it does more than that it's faulty!
 
Diesel Do said:
That happens when they stick open! If there wasn't as much burn it'd produce black smoke due to incomplete combustion of the injected fuel! EGR is only meant to replace the spare air. Which wouldn't affect expansion, it combines with nitrogen at high temps tho. A diesel doesn't regulate the amount of air like a petrol does. It always takes in as much as it can. So the excess air only is replaced! If it does more than that it's faulty!
Click to expand...

The EGR valve is controlled by the MAF sensor. That is the sole reason a MAF sensor is fitted if there was no EGR there would be no MAF sensor.That controls via the ECU and the EGR modulator how much exhaust gas is ingested and how much fuel is injected for certain engine conditions. I am not going to type out an essay on how it works, just go to RAVE and read the description in the emission control section for the diesel engine. You then may appreciate better what i am talking about.
 
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I appreciate that but doesn't the maf measure the volume of air going into the engine, so that for a set throttle position rpm etc it can calculate how much air is needed for the amount of fuel to be injected. Then it can open and close the EGR valve to reduce the air coming in to a level that there should be no spare oxygen after combustion. When the inlet air drops low it'll close when it increases it opens in a loop to regulate the amount of oxygen so that there is only enough to burn the injected fuel! That is controlled by the maf on a td5 but a 300 tdi relies on a very basic system with no maf
 
No throttle on a diesel...the air is constant pressure and volume - fuelling is what changes engine output....

The MAF has little to do with fuelling on a diesel beyond measuring O2...

(this ol'chestnut again)
 
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Just read the description in RAVE ref EGR and MAF sensor relationship. Read it a few times and digest. When the EGR is working the ECU only injects fuel for the fresh oxygenated air being drawn in through the MAF. When the EGR is open and exhaust gas is being ingested. Less new air will go through the MAF therefore the fuel quantity will be reduced. This is constantly adjusted to give best emissions. The EGR is not operative when the engine is being started. On the overrun. Or on maximum boost. It is operative under all other conditions. As i say read and digest the descriptive text.
 
wammers said:
Just read the description in RAVE ref EGR and MAF sensor relationship. Read it a few times and digest. When the EGR is working the ECU only injects fuel for the fresh oxygenated air being drawn in through the MAF. When the EGR is open and exhaust gas is being ingested. Less new air will go through the MAF therefore the fuel quantity will be reduced. This is constantly adjusted to give best emissions. The EGR is not operative when the engine is being started. On the overrun. Or on maximum boost. It is operative under all other conditions. As i say read and digest the descriptive text.
Click to expand...

Er! I think in my illiterate kind of way that's what I was saying! I'll have a read, but I was under the impression it just monitored air supply so it didn't put too much fuel in and cause smoke but it didn't actively reduce fuelling it regulated EGR to reduce spare oxygen and minimise nox.
The questions going to have to be when it's blanked off or removed with all that excess air why not more power if the maf controls the fuelling? Plus it doesn't explain non maf systems:)
I suspect we may not agree 100% but I'll settle for 99:D
 
wammers said:
Just read the description in RAVE ref EGR and MAF sensor relationship. Read it a few times and digest. When the EGR is working the ECU only injects fuel for the fresh oxygenated air being drawn in through the MAF. When the EGR is open and exhaust gas is being ingested. Less new air will go through the MAF therefore the fuel quantity will be reduced. This is constantly adjusted to give best emissions. The EGR is not operative when the engine is being started. On the overrun. Or on maximum boost. It is operative under all other conditions. As i say read and digest the descriptive text.
Click to expand...
Exactly what I have said all along, the MAF is used to adjust fueling:)
 
Diesel Do said:
Er! I think in my illiterate kind of way that's what I was saying! I'll have a read, but I was under the impression it just monitored air supply so it didn't put too much fuel in and cause smoke but it didn't actively reduce fuelling it regulated EGR to reduce spare oxygen and minimise nox.
The questions going to have to be when it's blanked off or removed with all that excess air why not more power if the maf controls the fuelling? Plus it doesn't explain non maf systems:)
I suspect we may not agree 100% but I'll settle for 99:D
Click to expand...

On a non EGR engine just as an EGR engine. Throttling is controlled by fueling. Fueling for any given RPM is extrapolated by the ECU from data like fuel temp, air temp, engine temperature, manifold pressure. This is preset by the map held within it. The throttle potentiometer indicates to the ECU what percentage of the throttle is required and fuel is increased until that speed is reached, as indicated by the crank speed sensor. Fuel is then held at that level until the potentiometer value is changed or any of the other sensor values are changed. In which case the fueling is adjusted to maintain the requested RPM. The EGR interrupts that cycle by introducing exhaust gas to cool the burn. Less fresh air then goes through the MAF so fuel is reduced to maintain mixture ratio. (Or you would get smoke or soot). That in turn reduces the power. Therefore to maintain that given RPM a slightly larger percentage potentiometer position is needed. That is why when the EGR is blocked the engine feels slightly more responsive. That is how i see it let me know if you think anything different.
 
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wammers said:
On a non EGR engine just as an EGR engine. Throttling is controlled by fueling. Fueling for any given RPM is extrapolated by the ECU from data like fuel temp, air temp, engine temperature, manifold pressure. This is preset by the map held within it. The throttle potentiometer indicates to the ECU what percentage of the throttle is required and fuel is increased until that speed is reached, as indicated by the crank speed sensor. Fuel is then held at that level until the potentiometer value is changed or any of the other sensor values are changed. In which case the fueling is adjusted to maintain the requested RPM. The EGR interrupts that cycle by introducing exhaust gas to cool the burn. Less fresh air then goes through the MAF so fuel is reduced to maintain mixture ratio. (Or you would get smoke or soot). That in turn reduces the power. Therefore to maintain that given RPM a slightly larger percentage potentiometer position is needed. That is why when the EGR is blocked the engine feels slightly more responsive. That is how i see it let me know if you think anything different.
Click to expand...

I wasn't talking about non egr! I was talking about non MAF! But I have read about the egr operation, and found no reference to the MAF reducing fuelling on a td5. It uses it as I said to monitor the amount of air going in so that the ECM can figure out how much exhaust gas to allow in, to replace the excess oxygen only! To allow optimum combustion with minimum nox gasses.
 
Diesel Do said:
I wasn't talking about non egr! I was talking about non MAF! But I have read about the egr operation, and found no reference to the MAF reducing fuelling on a td5. It uses it as I said to monitor the amount of air going in so that the ECM can figure out how much exhaust gas to allow in, to replace the excess oxygen only! To allow optimum combustion with minimum nox gasses.
Click to expand...

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? So what you are saying is the same amount of fuel for a given engine speed is injected whether the EGR valve is open or not. The EGR can optimally supply 50% of the charge as used exhaust gas, with the oxygen content of a fruit gum. What is going to happen if the same amount of fuel needed for a full oxygenated charge is injected. You would put a smoke screen up better than a WWII destroyer.


The MAF sensor, located in the air cleaner outlet pipe,
monitors the amount of air being drawn into the intake
manifold. This data is used by the ECM to calculate
the injected fuel volume, the intake air temperature
and the rate of EGR.
The MAF sensor is a hot film sensor which has a
heated surface maintained by an electrical current at a
constant temperature. With cool air flowing past the
sensor, the volume of air drawn into the intake
manifold is measured by the electrical current required
to keep the temperature of the hot film sensor
constant.

From P38 RAVE. TD5 EGR operates in the same way.
 
Last edited:
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!
Click to expand...
 
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!
Click to expand...

Does no one read things! I refer to a diesel with EGR and no MAF!
Click to expand...
 
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!
Click to expand...


As far as I can discover, the MAF was introduced on electronically controlled diesel injection to comply with stricter emissions regs. It means that the accelerator position and a rigid fuel map are replaced by a system where the amount of fuel injected can be more accurately controlled by measuring the amount of air being injested, so no momentary over fueling when you stamp on the accelerator. The accelerator effectively requests more fuel from the ECU which then ramps up fueling by the optimum amount in line with the rising air flow past the MAF. It still uses a fuel map but control is more flexible and precise. Re-mapping in principle simply puts more fuel in for a given air flow, so may result in potential emissions failure in the US for example.
Click to expand...
 
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? So what you are saying is the same amount of fuel for a given engine speed is injected whether the EGR valve is open or not. The EGR can optimally supply 50% of the charge as used exhaust gas, with the oxygen content of a fruit gum. What is going to happen if the same amount of fuel needed for a full oxygenated charge is injected. You would put a smoke screen up better than a WWII destroyer.


The MAF sensor, located in the air cleaner outlet pipe,
monitors the amount of air being drawn into the intake
manifold. This data is used by the ECM to calculate
the injected fuel volume, the intake air temperature
and the rate of EGR.
The MAF sensor is a hot film sensor which has a
heated surface maintained by an electrical current at a
constant temperature. With cool air flowing past the
sensor, the volume of air drawn into the intake
manifold is measured by the electrical current required
to keep the temperature of the hot film sensor
constant.

From P38 RAVE. TD5 EGR operates in the same way.
Click to expand...

The EGR valve is modulated by the control valve to vary egr gas flow. It can control the egr flow on a MAF system because it measures the amount of air for the amount of fuel it's going to inject. It doesn't just open and bung **** loads of egr thru it meters it because if it did do that performance would surely vary? I read that in the td5 rave manual where it made no reference what so ever about fuelling! Unless of course you're talking about egr on a petrol engine then you're talking completely different operating logic.

The MAF sensor, located in the air cleaner outlet pipe,
monitors the amount of air being drawn into the intake
manifold. This data is used by the ECM to calculate
the injected fuel volume, the intake air temperature
and the rate of EGR.

With reference to this paragraph, it says the data is used to calculate fuel volume! No argument there.
It also says it uses it to regulate the RATE of EGR! No argument there.
Where in the operating logic description does it state that it actively reduces fuelling when egr is operational? I'm afraid from what I'm reading you appear to be reading things into it that aren't there? An air flow meter is crucial for lots of things, but mainly it just measures the air flow:)
I dont think you're fruit gum argument works because it's basically implying that there is only ever enough air in the cylinder for the amount of fuel injected! On a diesel this simply isn't the case! If there was no spare air you would have no nox so not need egr! Egr only replaces the excess amount of air, the amount of egr is strictly controlled by the ECM based mainly but not solely on the data from the MAF. Clearly it uses that data for other things fuelling being one of them but I believe egr operation and fuelling adjustment aren't done together! the basis of your argument is that it controls fuel not egr? That's clearly not the case from your own evidence.
:)
 
Datatek said:
6704nathan said:
As far as I can discover, the MAF was introduced on electronically controlled diesel injection to comply with stricter emissions regs. It means that the accelerator position and a rigid fuel map are replaced by a system where the amount of fuel injected can be more accurately controlled by measuring the amount of air being injested, so no momentary over fueling when you stamp on the accelerator. The accelerator effectively requests more fuel from the ECU which then ramps up fueling by the optimum amount in line with the rising air flow past the MAF. It still uses a fuel map but control is more flexible and precise. Re-mapping in principle simply puts more fuel in for a given air flow, so may result in potential emissions failure in the US for example.
Click to expand...

That's how I see it to!
Click to expand...
 
The ECU injects fuel proportionally to the amount of air going through the MAF. It does not inject fuel for the portion of the charge made up by exhaust gas. If it did the result would be soot and smoke generation as a portion of fuel would never be burned. Easy to understand. Apparently not.
 
wammers said:
The ECU injects fuel proportionally to the amount of air going through the MAF. It does not inject fuel for the portion of the charge made up by exhaust gas. If it did the result would be soot and smoke generation as a portion of fuel would never be burned. Easy to understand. Apparently not.
Click to expand...

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:D
 
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