Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

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KevMayer
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by KevMayer » 16 May 2011, 20:58

This makes sence I believe because even though the EGR feeds exhaust gas back into the inlet, the ECU still needs to know how much fresh air is entering the engine so it can inject the correct amount of fuel to give efficient combustion.

The exhaust gas is inert and so, even though the fresh air is diluted by exhaust gas, the amount of oxygen admitted still needs to be acurately measured to know how much fuel to inject and this must surely be the main purpose of the MAF.

cachaciero
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by cachaciero » 16 May 2011, 22:27

Take a step back, consider an engine with no EGR system, does it need to know how much fresh air is being admitted to calculate the amount of fuel to inject? No! the ECU would calculate the amount of fuel to inject based upon the current engine speed and the throttle demand. The ECU can calculate that with no reference because a cylinder full of air for every induction stroke is a given.

Now you come to reducing NOX by restricting the amount of free oxygen. Reduction of free oxygen is basically achieved by replacing part of the inducted air with an inert gas, exhaust gas in this case. To get the value correct you have to measure the inlet fresh air as part of the EGR control loop to enable correct modulation of the EGR valve and Turbo.

So my assumption was engine speed and throttle position give fuel demand Mass air flow and engine speed control the EGR valve and turbo pressure, still don't really see that there is a need for the MAF to have anything to do with fueling. O.K I could concede that it might have a place for fine trimming of fueling but not the major effect that it has where it would appear to be the predominate controlling influence for fueling.
In some ways doing it this way almost makes the diesel induction work in a way which is akin to a petrol engine. On a petrol engine the ECU has to know the mass flow of air for fueling because it can make no oxygen assumptions based upon cylinder capacity due to the wide pressure range of the inlet side of a petrol engine caused by the action of the throttle valve.

cachaciero

dieselnutjob
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by dieselnutjob » 17 May 2011, 09:10

cachaciero wrote:Arranged a partial bypass of the MAF sensor and was extremely surprised at the precipitous drop in performance at the low end up to about 2k revs. If any one has ever driven these engines with the swirl valves permanently open it was like that only worse!.
Was it a permanent bypass?
I think that you need a switchable bypass that the ECU can control. When the ECU wants full power it can turn off EGR. If that resulted in the bypass turning off then you shouldn't see any power loss.

cachaciero
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by cachaciero » 17 May 2011, 22:29

Well if by permanent you mean fixed yes it was basically a hole just after the MAF so it was constant area from 0 to max revs.

It did seem to me that the power was down throughout the rev range from 800 to 3500. Climbing hills that I would normally be able to do in 2nd / 3rd @ 30 ish needed to go down to 1st / 2nd . On the straight and level acceleration from any speed in the range 0 -70 was down on what it would otherwise have been.
Given that the MAF has such a significant effect on fueling I feel that no benefit is likely to be obtained by bypassing it at any speed range.

What I believed was that the MAFs prime function was in effect to modulate the turbo to regulate air to exhaust gas ratio, then by bypassing it it would cause the boost pressure to rise with corresponding performance increase for the same amount of injected fuel.

I wonder if there is profit in playing with the Turbo Pressure sensor............

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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by KevMayer » 17 May 2011, 22:57

I've thought about playing with the pressure sensor.

If a longer pipe were fitted from the intercooler to the sensor with a bleed valve in it then it could be tricked into measuring a lower pressure than is present. This would make the turbo boost slightly more.

I have some rubber pipe and a bleed valve in my garage :lol:

dieselnutjob
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by dieselnutjob » 18 May 2011, 16:24

cachaciero wrote:What I believed was that the MAFs prime function was in effect to modulate the turbo to regulate air to exhaust gas ratio, then by bypassing it it would cause the boost pressure to rise with corresponding performance increase for the same amount of injected fuel.
No that isn't true.

The ECU uses the boost pressure sensor as feedback to control the turbo.

The MAF has two purposes:-

1. The ECU will not inject more fuel than there is air available to burn it. It calculates this by using the MAF to measure the amount of air flowing in. If you reduce the air going through the MAF then you reduce the maximum fuel that the engine will inject.

2. If the ECU calculates that there is too much air flowing into the engine then it will attempt to reduce it by opening the EGR valve. The purpose of this is to reduce NOx emissions.

You need a MAF bypass that the ECU can modulate (switch) using the EGR control signal.

When you demand maximum power the ECU will close the EGR (except it will now be closing the bypass instead). This will give you maximum flow through the MAF and therefore maximum power.

When you are not demanding maximum power the ECU will try to reduce air flow by opening the EGR, but instead it will open the bypass which will reduce air going through the MAF and it will be happy.

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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by myglaren » 18 May 2011, 17:14

dieselnutjob wrote:1. The ECU will not inject more fuel than there is air available to burn it. It calculates this by using the MAF to measure the amount of air flowing in. If you reduce the air going through the MAF then you reduce the maximum fuel that the engine will inject.
This then could be the reason for poor performance? If an incorrect (low) airflow is reported by the MAF then the ECU will reduce the volume of fuel injected?

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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by cachaciero » 18 May 2011, 17:17

Ah! that makes sense, just need to find a suitable vac operated butterfly valve, although I can forsee possible problems with hunting between the new air valve and EGR valve me thinks it might be easier just to get it re-mapped :-)

EDIT Forget the hunting bit the EGR valve remains firmly closed it's just the new air valve that would open, Really the optimum would be to use the EGR valve with the exhaust side open to air.

EDIT 2 No that won't do outlet side needs to be on low pressure side of Turbo, still a surplus EGR valve might be a good candidate.

cachaciero
Last edited by cachaciero on 18 May 2011, 21:47, edited 2 times in total.

cachaciero
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by cachaciero » 18 May 2011, 17:51

myglaren wrote:
dieselnutjob wrote:1. The ECU will not inject more fuel than there is air available to burn it. It calculates this by using the MAF to measure the amount of air flowing in. If you reduce the air going through the MAF then you reduce the maximum fuel that the engine will inject.
This then could be the reason for poor performance? If an incorrect (low) airflow is reported by the MAF then the ECU will reduce the volume of fuel injected?
In a word yes, makes you think about non OEM parts and the standard of their calibration :-)

Oh! and low airflow does not post any warnings.

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dieselnutjob
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by dieselnutjob » 19 May 2011, 16:11

I don't think that you will need a pressurised source of air.
You have already proved that an opening just after the MAF results in a reduced MAF reading.
A simple vac operated throttle which allows clean air to get into the engine without going through the MAF will probably be good enough.

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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by cachaciero » 19 May 2011, 17:26

dieselnutjob wrote:I don't think that you will need a pressurised source of air.
You have already proved that an opening just after the MAF results in a reduced MAF reading.
A simple vac operated throttle which allows clean air to get into the engine without going through the MAF will probably be good enough.
Yes your right had already got there see EDIT2 :-) was thinking that a spare EGR valve would be about the right size and Vac operated, although this is a poppet valve and not a butterfly however don't know if it requires a lot of pressure underneath to open.

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dieselnutjob
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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by dieselnutjob » 19 May 2011, 17:38

I have no whether an EGR valve will open simply with vacuum applied and without any pressure to help it.
I guess the only way is to connect it to a vac line, start the engine and see if it opens.

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Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by cachaciero » 19 May 2011, 18:11

dieselnutjob wrote:I have no whether an EGR valve will open simply with vacuum applied and without any pressure to help it.
I guess the only way is to connect it to a vac line, start the engine and see if it opens.
First find an old EGR valve :-(

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Re: Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by corsehf » 13 Feb 2012, 22:48

Further to my comments about a year or so again regarding the state of the intake manifold and butterfly valves on the 2.2, i have cleaned out my (newer) steed last weekend and the state they were in is appalling.
I have taken pics this time (however the pics are too big??) and the crud on the valves measured between 5 - 6mm on both sides!!
No way can this be good?

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Re: Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

Post by myglaren » 13 Feb 2012, 23:10

corsehf wrote:Further to my comments about a year or so again regarding the state of the intake manifold and butterfly valves on the 2.2, i have cleaned out my (newer) steed last weekend and the state they were in is appalling.
I have taken pics this time (however the pics are too big??) and the crud on the valves measured between 5 - 6mm on both sides!!
No way can this be good?
Upload the pics to PhotoBucket and paste the thumbnail link here.