I’ve been talking about the 'EGR Delete' to my mate, who’s a really good mechanic, and how it throws up a CEL light.

Well, we think we've cracked how to do the delete, without throwing up a light, or any VAG-Com type stuff.

To understand how to do this, I need you to understand how the EGR works.

The reason for the EGR is to drop the emitions, and lower fuel consumption.

The way it works is, it puts exhaust fumes back into the inlet manifold.

The way it does it (from my understanding) is a sensor senses boost and opens the EGR up. The MAF sensor senses the drop in air breathing through (because the engine is sucking from the exhaust too).

So when you take the EGR out, the MAF doesn’t sense this drop, and thinks the EGR is knackered and throws up the CEL.

So, to keep the CEL from coming on, the MAF needs to detect a pressure drop when the EGR is open.

Here’s what we think may be the fix...

Take the EGR cooler off and blank the exhaust manifold with a proper blanking plate.

Find where the exhaust fumes go into the EGR and attach a silicon hose.

Attach the other end to the clean side of the air filter, there for bypassing the MAF.

So what should happen is when the Sensor senses the boost, it tells the EGR to open, which it does... However, rather than sucking fumes, its sucking clean filtered air. But the MAF still detects the drop in pressure (because the EGR is still sucking and there is still a drop in pressure for the MAF to sence, but its all clean).

Any opinions welcome. (Especially from the likes of Awesome and Jabba).

I will try my theory out soon, and see if a light comes on. Not really any reason it should though.

Dave

Edited 25 March, 200917 yr by Lofty86

i don't think it'll work as the air the egr is letting in is under pressure so its not sucking anything in its simply letting it by but if it works well done

I did wonder this, but I didnt know if the pressure drop would be enough to not show the CEL??

One way to find out I suppose. Just gota save for some silicon hose (god thats poor isnt it?!).

Dave

Yeah I thought of this too and thought also what you have. The air from the air filter end would not have enough pressure. This would cause a boost pressure loss near the egr.

I suppose it depends how much pressure those egr exhaust gasses come out at.

You can avoid a CEL with a remap.

EGR is used to lower combustion temperatures and thus harmful NOx emissions.

at a decent pressure i would expect seeing as its exhaust gases.

You thinking of it the wrong way around.

As the flap closes it creates a vacuum or depression which sucks the exhaust gases into the intake manifold.

i fully admit to having absolutely no clue how it works.

What about fuelling for the clean air you're putting in that isn't being metered by the MAF?

When recirculating exhaust gas no more fuel is needed because that part of the combustion mix cant be burnt but you're now adding more air(oxygen), but no more fuel, whereas blanking the egr and getting it mapped properly allows the MAF to see the change in air flow and add fuel accordingly.

If you get my drift.

Kev

What about fuelling for the clean air you're putting in that isn't being metered by the MAF?

When recirculating exhaust gas no more fuel is needed because that part of the combustion mix cant be burnt but you're now adding more air(oxygen), but no more fuel, whereas blanking the egr and getting it mapped properly allows the MAF to see the change in air flow and add fuel accordingly.

If you get my drift.

Kev

So in theory your EGR delete means the fuel your already throwing in, will burn cleaning, so less smoke? Or same smoke more power depending which one you prefer?

If you get my drift.

Aaah, I do indeed Kev.

Hadnt thought of that.

So that could be the end of that plan then. Theroy was sort of there tho.

Dave

I'm pretty sure that EGR is not activated on high revs. Only below 2000 rpm. And if you blank it with blanking plate, it shouldn't trigger CEL. EGR is vacuum controlled, not electronically, it doesn't know are the exaust gases entering manifold or not. I have blanked EGR on friends A3, 1.9 PD, almost 20 000 miles, no CEL...

I'm pretty sure that EGR is not activated on high revs. Only below 2000 rpm. And if you blank it with blanking plate, it shouldn't trigger CEL. EGR is vacuum controlled, not electronically, it doesn't know are the exaust gases entering manifold or not. I have blanked EGR on friends A3, 1.9 PD, almost 20 000 miles, no CEL...

Strange, that should have thrown up a CEL light.

I know its vacuum controlled, and runs on low revs, but thank you for pointing that out, as i hadnt.

It should know when theres EG's going into the manifold, otherwise you should be able to just take off the EGR valve without any problem.

I put a blanking plate on a TD5 and it didnt like it after about 150 miles or so.

I'll have to talk to my diagnostics guy, and he will probably know straight away.

Dave

EGR runs at idle and very light throttle application.

It can't run when the turbo is going as it would act as a wastegate.

The CEL should come on as its a looped system with a feedback, as soon as it doesn't see an EGR flow it will flag a fault. Block an EGR port and you will soon have issues.

I'm pretty sure that EGR is not activated on high revs. Only below 2000 rpm. And if you blank it with blanking plate, it shouldn't trigger CEL. EGR is vacuum controlled, not electronically, it doesn't know are the exaust gases entering manifold or not. I have blanked EGR on friends A3, 1.9 PD, almost 20 000 miles, no CEL...

It is electronically controlled, the vacuum comes from a duty cycled solenoid that is controlled by the engine ECU.

IIRC the more recent ECUs are even more trigger happyu for the CEL - and the EGR delete hardware made the CEL come up pretty sharpish, as Ross says, it is ECU controlled and checked, so the only way to remove it is to map out the light or remove the program piece that deals with EGR. The latter is the correct way

It is ECU controlled, I agree, but how can it know are there any exaust gases entering manifold or not? There is no sensor on manifold. Or I'm missing something...

It knows the airflow (MAF) and it knows the absolute pressure (MAP). I guess it does some calculations there, but would have to wait for Ross as he's just done a course on this so he'll probably know

A bit late i know, But i was also looking at a way around the CEL. once I had mine pop up we re connected the VACUME hoses only to the EGR and on startup of the car the egr flap moved twice and then the CEL went.... So i thought it was the vacume presure that pipcked up if it was there.

Airflow gives the ECU information on amount of air entering engine, so it can deliver enough fuel. MAF is located before the EGR, so amount of air is measured long before the manifold. Understand where I'm going with this?

And the MAP just measures boost pressure. Or am I mistaking?

The MAF (mass air flow) sensor detects flow of air. When the EGR is open, the air flow drops, and thats how the ecu knows if its working or not.

And yeah, it would leak boost if it worked while the turbo was spinning. So it is defenatly only working off boost.

Dave

You thinking of it the wrong way around.

As the flap closes it creates a vacuum or depression which sucks the exhaust gases into the intake manifold.

Venturi?

This flap, is it the same flap as the anti-shudder valve?

This flap, is it the same flap as the anti-shudder valve?

Yeah. Thats the one.

So if you do a EGR delete, you will loose your engine safty cut off valve.

Dave

And you can tell, it shudders when you turn off the ignition.

As a diesel engine doesnt create manifold vacuum the flap is needed so create a depression behind it to draw the exhaust gas from the manifold. When the EGR is operated you have effectively created an air leak into the system. The MAF will see this as the intake of air will drop (as mentioned) from this it knows that EGR is in operation.