Some thoughts on the 2.2 C5 EGR SYSTEM (Long)

corsehf · Post by **corsehf** » 06 May 2011, 14:05

Was there any conclusion to all this info, like - Can we remove the EGR along with the DPF, Eolys fluid and possibly Cat and have a car that drives like it should ??

cachaciero · Post by **cachaciero** » 07 May 2011, 15:53

Removing the FAP, CAT and disabling the Eolys system is quite do-able however the ECU will need to have some re-mapping done OR the diff pressure sensor input frigged to make the ECU believe that it has a clean FAP. Will that make it drive like the 173hp version?, hardly

.

Removing the EGR system is much more problematical and I don't believe that it can be done in a way that will give performance improvements with out bringing up warnings and limp mode, at least not without some substantial re-programming of the ECU. I may be wrong but that is my opinion.

The EGR system as such if well designed (and that's questionable in this case) should not impact upon performance, removing it will increase running temperature and reduce carbon particulates.

I believe that as it stands the engine is under-boosted through much of it's rev range and that to get more out of it would require increasing the boost pressure and a corresponding increase in intercooler size which actually appears to be what they have done on the 173BHP engine.

I suspect that much of the performance increase that comes from removing the FAP is as much due to improved turbo performance as it is to reduction of back pressure caused by the FAP .

Some areas I have thought about "playing with"

Turbo Modulation check that it works properly, see if it is possible to adjust it to increase turbo boost.
Turbo pressure sensor, if turbo boost is increased this sensor may require to be offset electrically to prevent the ECU detecting overboost.

If the EGR system is disabled by blanking off the inlet or disabling the Electrovalve then as I understand it the MAF will / should detect a flow error and the ECU throw a wobbly, investigate ways of altering the MAF output such that it is within acceptable limits with a disabled EGR system. This later bit is an attempt to remove EGR without ECU re-programming.

As you can see this is a fair bit of work not without some risk of blowing the engine and frankly I have come to the conclusion that life is to short, far easier to buy a 173 Bhp MkII which has additional benefits, provided you don't want an auto.

The ideas are put forward for others to think about and play with if they so wish I would certainly be interested in the results of any such work done but I am not going there

cachaciero

Clogzz · Post by **Clogzz** » 08 May 2011, 15:50

Blanked off the EGR on the petrol car and it indicated anti-pollution fault on the first trip.
Restoring flow cleared the indication after three restarts.
Disconnecting the electrovalve also soon indicated anti-pollution, and after reconnection it took about a month for the display to clear.

I’ve read stories of needing 40 restarts from under 22°C with reaching an engine temperature of 77°C to clear the disconnection fault.
If true, I don’t know how it went because in summer we don’t go below 22 for months.

cachaciero · Post by **cachaciero** » 08 May 2011, 17:16

Well three start / run cycles is the norm to clear an intermittent fault,
a month for the EV connection /disconnection makes me wonder if there is / was a bit of a vacuum / electrical intermittancy but then it is a Cit

Your are confirming my theory about EGR blanking which should be of interest to anybody going down this route.

cachaciero

dieselnutjob · Post by **dieselnutjob** » 09 May 2011, 09:12

corsehf wrote:Was there any conclusion to all this info, like - Can we remove the EGR along with the DPF, Eolys fluid and possibly Cat and have a car that drives like it should ??

That's exactly what I have done on my 607. It's a 2001 model though. The DPF and Cat where removed about four months ago and the EGR blanked maybe a month ago. No problems yet.

corsehf · Post by **corsehf** » 09 May 2011, 15:09

cachaciero wrote:Removing the FAP, CAT and disabling the Eolys system is quite do-able however the ECU will need to have some re-mapping done OR the diff pressure sensor input frigged to make the ECU believe that it has a clean FAP. Will that make it drive like the 173hp version?, hardly .
cachaciero

I had the DPF and Eolys system removed from my last C5 and it's just a case of telling the car that it's no longer fitted via a Lexia.
I was just wondering if the same could be done with the EGR system??

cachaciero · Post by **cachaciero** » 09 May 2011, 22:01

dieselnutjob wrote:
corsehf wrote:Was there any conclusion to all this info, like - Can we remove the EGR along with the DPF, Eolys fluid and possibly Cat and have a car that drives like it should ??
That's exactly what I have done on my 607. It's a 2001 model though. The DPF and Cat where removed about four months ago and the EGR blanked maybe a month ago. No problems yet.

Ah! yes! I thought I had read that somewhere

. Well I can only say that I believe that the MAF should detect an error and flag it but........

Interesting that some have done what you have done and get errors posted and others don't. I wonder.....how good is your MAF sensor one needs a way of measuring flow (actually mass flow) and comparing it with what the Lexia says.

cachaciero

cachaciero · Post by **cachaciero** » 09 May 2011, 23:02

I was going to let this drop but coming home from work a thought and questions entered my head.

MAF's

One reads several instances of rough running / poor performance being cured by fitting a new MAF, I have often wondered why the MAF should cause poor running and why given it's construction should it fail at all. Then it came to me.

When the engine is in the EGR regime the MAF will I believe be the main controller of the Turbo (speculative statement!).

The EGR calculation is based upon mixing exhaust gas into the manifold such that there is just sufficient oxygen in the mix to allow combustion of all the injected fuel.

Now within the EGR regime the ECU "knows" how much fresh air is going into the engine by virtue of data from the MAF, it has calculated how much fresh air it needs so it will modulate the Turbo to get the correct amount.

However while the system can measure accurately the amount of fresh air in the system it has no equivalent measure of the amount of exhaust gas entering the system.

The amount of exhaust gas can only (on the 2.2) be calculated based upon a theroetical map based upon EGR valve opening and a theoretical map of exhaust gas pressure, so if the EGR valve is not in the position the ECU thinks it is (no EGR feedback on 2.2) or exhaust gas pressure is different to what it believes it should be the ratio of fresh air to exhaust gas will be wrong. If the system calculates that there is to much fresh air in the system (even if there isn't) it will reduce boost so this is a double whammy in terms of reducing performance.
I do wonder if all the component tolerances go in the wrong direction if the system is right on the edge of acceptable performance if so it would only require a slightly sticky EGR valve bit of an exhaust leak, turbo slightlly below par small air leakage after the MAF to produce a marked reduction in performance /economy.

Sorry this is a bit rambling need to do a little more research but i give it you as "food for thought / comment"

Interestingly the 2.2 173 bhp engine has a lamda sensor in the exhaust this would enable a much more accurate way of measuring oxygen content in the exhaust and thus enable a truly closed loop EGR control system.

cachaciero

Clogzz · Post by **Clogzz** » 10 May 2011, 13:00

Don’t know about the diesels, but on the petrol car the ECU opens the valve when decelerating to see if the MAP sensor will find out.

cachaciero · Post by **cachaciero** » 10 May 2011, 21:37

Clogzz wrote:Don’t know about the diesels, but on the petrol car the ECU opens the valve when decelerating to see if the MAP sensor will find out.

What valve? Petrol engine? that must have a throttle valve in the inlet, if that was controlled by the ECU it would make sense when decelerating to open it, with fuel shut off I guess it would increase the engine braking effect, or are we talking EGR valve do petrol engines have EGR and if so why, I can feel confusion coming on a pace

cachaciero

dieselnutjob · Post by **dieselnutjob** » 10 May 2011, 22:39

cachaciero wrote:
dieselnutjob wrote:
corsehf wrote:Was there any conclusion to all this info, like - Can we remove the EGR along with the DPF, Eolys fluid and possibly Cat and have a car that drives like it should ??
That's exactly what I have done on my 607. It's a 2001 model though. The DPF and Cat where removed about four months ago and the EGR blanked maybe a month ago. No problems yet.
Ah! yes! I thought I had read that somewhere . Well I can only say that I believe that the MAF should detect an error and flag it but........

Interesting that some have done what you have done and get errors posted and others don't. I wonder.....how good is your MAF sensor one needs a way of measuring flow (actually mass flow) and comparing it with what the Lexia says.

cachaciero

I think it depends on the year. Mine was built in December 2000 so it's a very early model. My year 2000 806 HDI also has the EGR removed and no error light.

There probably is an error code logged in the ECU but it's not considered serious enough to put the light on.

On later model the software was changed to flag a warning if the EGR isn't working.

I have heard of people with VWs wiring up diodes and resistors so that when the EGR solenoid is activated the signal to the solenoid is used to reduce the output of the airflow sensor. This has the effect of fooling the ECU that the EGR is having the desired effect.

From memory on a VW the EGR solenoid is negative switched so you can use the pull down effect to pull down the airflow sensor output a bit. Not sure about HDIs though.

Clogzz · Post by **Clogzz** » 11 May 2011, 12:52

What valve?

The petrol engines have an EGR electro valve to reduce nitrous oxides at light loads, somehow just when the output of Nox is already low.
They have a motorised throttle for air only and it’s nearly closed when decelerating, so causing a deep vacuum.
The ECU then opens the EGR electro valve to cause a reduction in vacuum that the MAP sensor must detect to confirm opening of the EGR valve.

cachaciero · Post by **cachaciero** » 11 May 2011, 13:04

Well for those of you that have the desire and time to experiment.......

My one brain cell has led me to the conclusion that it would be interesting to play with bypassing the MAF.

If the theory is correct lower flow through the MAF should provoke the system into increasing boost to compensate, but what if all the air didn't go through the MAF only some of it ? Then if the theory holds good turbo pressure should be increased throughout the EGR operating range, maybe the whole rev range while the EGR valve would proportional be more closed. Shouldn't be to difficult to cobble up a bit of pipe to go from the back of the MAF to the plastic duct needs to be a hole in this pipe gut feel says it needs to be about an inch in diameter, this needs to be variable to play with but a bit of sticky tape could be used to play around with area. If there is benefit then a permanent set up could be made up with the bypass pipery going back to the filter housing.

cachaciero

dieselnutjob · Post by **dieselnutjob** » 12 May 2011, 20:44

that would work
if you could rig up a vacuum operated MAF bypass you could drive it with the EGR solenoid
when the ECU wants more EGR the valve would bypass more air away from the MAF and the the ECU would be happy
There are some flaps on a 2.2 that select interooled or non-intercooleed air
maybe they could be adapted

cachaciero · Post by **cachaciero** » 16 May 2011, 16:41

Yes one would have thought so but it doesn't

Tried a little experiment of my own today, in spite of saying I wasn't going to.

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!.
I was really gob smacked at just how bad it got, no warnings and no power either.
The only thing that can explain this is that contrary to my belief the MAF has a major effect on fuel mapping which at least confirms and explains why many have had performance issues which have improved by changing the MAF.
So in summary the MAF appears to plays a major part both in air control and fuel control, as part of the EGR system so there is no simple way of modifying the EGR characteristics by tarting around with the MAF on it's own.

cachaciero