Lacking EGR: Worth the investment to replace?

[NoD~]

Back in my racing days, EGR blockoff plates were thrown on my engine and the rest was recycled. Doh! Little did I know I should have kept those parts laying around...

Fast forward to now, I want more MPG. But the price of replacing the EGR system isn't cheap.

What kind of gains does an EGR system actually offer? (For me, this is on a 2.0L SOHC Dodge Neon, but I ask this question for general knowledge as well)

[mikeyjd]

I could be wrong but I'm pretty sure egr systems decrease fuel economy for the sake of improved emissions quality. I suppose a well developed egr might possibility be a break even situation? You might already have a built in mpg increase on your hands

[RedDevil]

An EGR feeds exhaust air back into the air intake. It adds volume and heat to the mixture without adding oxygen. This helps the engine to run economically when on light load.

On light load the throttle plate will be almost closed, creating a strong vacuum on the rest of the air inlet trajectory. The first stroke of the Otto cycle sucks the air into the cylinder, and when that's a strong vacuum that requires more energy than when it's not; the so-called pumping loss.

When the EGR feeds warm burnt air into the inlet, the vacuum will be less strong, the heat helps complete combustion and unburnt fuel gets a second chance.

OTOH, your engine was designed to accept hot air from the EGR, so you can build a WAI or HAI instead. Clean hot air is less dense than cold air so it will reduce pumping losses.
I did plan to make a regulated WAI for some time, but I found that as my car does have EGR the added effect of the WAI becomes detrimental once the engine is fully warmed up.

[Daox]

It might be worth it if you can find some cheap ebay parts. Paying for a new EGR valve? Nah, they're expensive.

[AndrzejM]

Don't know exactly how EGR affects FE in gasser (haven't tested it) but in my TD by mistake I was driving for 2 tanks with EGR constantly closed, after fixing vacuum lines for egr valve I've noticed noticeable increase of FE. So IMHO it's worth to try to fix it if you can find some used cheap parts.

[oil pan 4]

Originally Posted by mikeyjd

I could be wrong but I'm pretty sure egr systems decrease fuel economy for the sake of improved emissions quality.

Thats true for most large diesels.
For some reason the small diesels like EGR. I think it helps them get up to and stay at operating temperature.

[mwebb]

EGR is INert gas - it displaces air fuel mixture

cooler EGR is thought to be better than hot EGR which is why many systems use EGR coolers , some systems that vary valve timing and overlap to get the EGR can not use EGR coolers

although incoming EGR gases are hotter than ambient air
even if fed through an EGR cooler
, when EGR is active
COMBUSTION TEMPERATURE always DECREASES relative to when EGR is not active

when EGR is active , engine displacement /engine size is reduced by the amount of EGR flow .
so a 2 liter TDi becomes a 1 liter TDi with 50% EGR flow
less so with gasoline powered systems which will not tolerate any where near 50% EGR flow

EGR when active
reduces the amount of air fuel mixture in the combustion chamber , creating a cushion and thereby reducing effective engine compression and reducing combustion pressure
which reduces combustion temperature
which reduces NOX emissions , which is a very good thing
which is the primary reason EGR was designed and implemented

EGR is inert gas , it does not change mixture in any way and does not and can not make the system lean or rich IF operating as designed

on a speed density system , systems that use MAP sensor s
EGR problems can change fuel trim significantly

EGR when active displaces incoming air fuel mixture
so less fuel is used , the engine produces less power for the same throttle opening so
the driver opens the air plate to get the same power , which improves Volumetric efficiency , slightly

thus improving fuel economy a wee but measurable amount
EGR is good

[Occasionally6]

The gain won't be dramatic but will be noticeable. Something around 5% (10% max) would be about right. You will get more back than you would by fitting it to an engine that never had it because the ECU will be mapped on the basis of it working (unless the mapping has been changed to suit the disabled EGR).

The air:fuel ratio will have been pulled back to stoichiometric by the ECU with feedback from the O2 sensor even with a speed-density (MAP sensor) system so that won't have any effect (unless the provision for correction was exceeded). However, the ignition timing won't have changed and will currently be overly advanced (mapped for EGR) without the EGR present. That's why you'll get more back than fitting one from scratch.

Surely the parts required are going to be very cheap from the junkyard. The valves (EGR valves in general, not specifically those used in the Neon) do get blocked up with combustion residue so you'll have to clean it, but they're pretty reliable otherwise.

With engine management in place the EGR is not usually (although it may be in later cars) active at WOT so it doesn't cost any power. (Other than the small weight reduction, it was really stupid to remove it.)