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Discussion Starter #1
Well, while working on the brake booster (another post) I had all the intake plumbing removed up to the intake manifold and the crap that was in the manifold around and after the EGR plumbing entrance was astounding! A thick, oily, grungy mess that blocked much of the intake at that point (engine has almost 350,000km on it.)

So, I put a 15mm stiff hose on a vacuum cleaner and scraped and sucked out as much of it out of the intake manifold as I could (a fair bit) and cleaned the EGR connection pipe then disabled the system.

Here's how (no blanking plates needed):
- make sure the EGR valve is closed and making a good seal (it opens under vacuum)
- unplug the vacuum hose that goes from the servo actuator to the EGR valve and plug the servo (you don't want to lose vacuum or such crap into the servo.) I used a small screw that threaded into the servo easily without cracking the plastic. There are other ways too.
- remove the vacuum hose that goes to the air doser. This is the bit that bolts on to the intake elbow and has a vacuum actuated butterfly valve that restricts the intake so that the EGR gasses are sucked into the engine. The air doser and the EGR valve are both controlled by the ECU via the vacuum servos. Plug up the air doser servo as well.

Done! No blanking plates or other pissing about. The ECU still activates the vacuum servos but nothing happens and it doesn't seem to care - at least as far as I can tell, I don't have a ECU code reader.

The engine runs great! I haven't had a long enough run to see if there is any fuel economy benefit.
 

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TL;DR: pull and bung the vacuum supply to the EGR.

Good point that you can do the same for the air doser.

The ECU knows that something is up because it sees more fresh air than it was expecting coming in through the MAF. This usually produces an 'intermittent' fault (no EML).

When the ECU sees this high MAF value it deduces that not enough fresh air is being recycled and therefore uses the air doser to throttle fresh air. However, even if the air doser is not disabled it seems to know not to throttle to the extent to cause a stall.

The air doser closes completely when you turn the engine off to prevent run-on. With it disabled you may notice a delay between you turning the key and the car stopping, and the car may shake more.
 

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Discussion Starter #3
Air doser

TL;DR:
What do TL and DR mean?

The air doser closes completely when you turn the engine off to prevent run-on. With it disabled you may notice a delay between you turning the key and the car stopping, and the car may shake more.

I don't see how the air doser can close at engine shut off because there is no vacuum to actuate it - its resting position is open, held by a spring that the vacuum works against to close it. Does it close momentarily using the last of the engine vacuum at shut-down? I know someone with a Citroen with the same motor that had a run-away diesel situation due to some sort of failure and I would have thought that if the air doser closed at key-off it would have prevented that (the kids driving the car just jumped out and ran as the engine red-lined!)

I might run a tank of fuel through with it disabled and then re-connect it and do the same to see if there is any performance difference.
 

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Discussion Starter #4
Fuel economy

Well, after running a few tanks of fuel through with the EGR system disabled I am confident enough to say there is a significant increase in fuel economy. Without changing driving style or routine routes it is now getting 5.7L/100km whereas before it was 6.3 - a 9.5% decrease in fuel use!

So, what makes less pollution - A: a car burning less fuel per km or B: a car burning more fuel with an EGR system? I would say A...
 

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There is no reason disabling a properly working egr system should improve fuel economy, however cleaning out the inlet manifold certainly might.
Now you are producing more nox, a highly toxic greenhouse gas.

Roger.
 

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Discussion Starter #6
True, the vehicle may now produce more NOX but the question is does it produce more per km travelled and litre of fuel burned? And yes, I understand that it is more likely the cleaned intake than the disabled EGR that is responsible for the decrease in fuel use.

I fully agree that a brand new motor on a test bench with an EGR system will produce less NOX than a motor without one but that's not what we have here. It is an engine with 350,000kms on it and I'm expecting to get to at least 500,000kms.

The EGR system combined with the stock crankcase ventilation system create a situation that steadily degrades engine performance over time. From what I can see it's a bit of "engineering to legislation" for new car pollution compliance, not a well thought out long-term solution because Peugeot wanted to make a difference to the environment.

I would think that an engine at maximum efficiency would produce less undesirable by-products. Without the test equipment required and checking the NOX levels before and after the intake clean out there is no way of actually knowing the true answer. Having access to the ECU mapping to determine when the EGR is actually introducing exhaust into the intake would be a good first step.

Once I install and test a "catch-can" in the crankcase ventilation system and am confident that oil mist is no longer being introduced to the intake I will re-enable the EGR system as it is the combination of the two inputs that creates the problem.
 

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The doser on the intake does indeed close momentarily at key off to help stall engine quicker.

As for EGR systems although they are good in principle i totally agree with the logic that if the engine uses more fuel it makes more pollution EGR systems are a double edged sword what you gain in reduced pollution you loose in more fuel used so in reality it does not really make much difference.

Older 406 2 litre 110 hp engines done 45 mpg all day long some done better with a light foot
The last of them with revised software were doing 38 average sometimes less ! even with the light foot.

Thats 15-20% MORE fuel being burnt and that cannot be good for environment !
 
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