Diesels and EGR

[COcyclist]

I have been reading up on EGR and mpg and it seems to help in gasoline engines. It makes the engine act like a smaller engine and reduces pumping losses. There is less vacuum working against the throttle plate so the engine is more efficient at part throttle. A diesel doesn't have a conventional throttle plate so does EGR help mpg or efficiency on a diesel??

[Gasoline Fumes]

I know two people with TDIs. One of them disabled the EGR. He hasn't had any change in mileage that I'm aware of. I get paid to clean out the other guy's intake manifold. It's not hard to temporarily disable the EGR to test the MPG difference. But you will increase the NOx emissions and get a check engine light.

[COcyclist]

Thanks Gas Fumes, Do you still have to clean the intake manifold since low sulpher diesel? My car is a 2004 PD with the O2 sensor. I have been told that my car won't run very well with EGR blocked unless I reprogram the computer.

[UFO]

When I ran with disabled EGR in my TDI (with CEL set) it made no significant difference in economy. However it made a huge improvement (about 10%!) in the fuel economy of my Jeep CRD, and that has a modification that tricks the ECU so it doesn't set a CEL.

So I am working on the same device for my TDI and will document any differences here when I do that.

[Big Dave]

It varies from engine to engine.

Doesn't seem to help VW TDI engines.

It helps Ford 6.0 and 6.4 engines a lot as it does the Cummins 24 valve.

[NachtRitter]

Originally Posted by Gasoline Fumes

... But you will increase the NOx emissions and get a check engine light.

My understanding is that you will bump the NOx emissions quite a bit if disabling the EGR on the diesel ... cat can't handle the higher NOx emissions (whereas it can handle the other emissions much better) ... and the NOx is the nasty of the possible emissions (responsible for acid rain, ozone (smog) creation, health probs, etc etc).

[UFO]

The catalytic converter on most diesels is an oxidation catalyst and is not designed to deal with NOx. Disabling the EGR will have no effect on the cat.

[NachtRitter]

Ah, OK... so then the higher NOx emissions would just pass right through into the atmosphere?

[Gasoline Fumes]

Originally Posted by COcyclist

Thanks Gas Fumes, Do you still have to clean the intake manifold since low sulpher diesel? My car is a 2004 PD with the O2 sensor. I have been told that my car won't run very well with EGR blocked unless I reprogram the computer.

It wasn't long ago that I cleaned it and he had it cleaned by somebody else a couple of years before that. He's running WVO most of the time too. Still gets clogged with a black sooty tar. It's a 1999.5 TDI. The other one with the EGR disabled is a 2002 TDI running on diesel only.

[JasonG]

They put cats on diesels now?
What next, spraying pee pee into the exhaust?

On a TDI I believe you can reprogram the computer to use the EGR when cold but close it off when warmed up. Seems Fred's TDI Page. TDIClub.com. VW TDI Enthusiast Community had a tutorial on this. TDI FAQ