Thread: People with No EGR's - Question for all of you

Haha, well it came with the header, I would hope it would work.

Then I will have to research a resistor mod for the EGR system

Bingo!! Under WOT the EGR system shouldn't be functioning. If it is you need a proper tune to remedy the situation. But, EGR gas is inert, non-burnable since is exhaust. Unless you have something seriously wrong with the tune of your engine there should be no way EGR can alter the mixture. The way EGR works is by displacing some of the incoming proper mixture with an inert gas.

Dms is correct. Unless your egr is f'd than its closed at wot so output will be a wash. I have run both with and without egr and consistantly see an improvement of .75-1.25 mpg with egr as apposed to without. Same car, same gas. The concept of egr is primarily to keep egt temps down during cruise and thus keeping nox from beeing formed. Nox turns into the nasty brown crap called smog when it goes through a chemical reaction with the air and sunlight. A side effect, if you want to call it that, is that by introducing an inert gas into the chamber some space is taken up that would be filled buy a stoich air/fuel charge. You may be able to debate the recouping of some unburned fuel in the exhaust streem, but if its that rich you have many other issues to work out. Another way egr improves mileage, is by reducing cyl temps, more spark lead can be used during cruise. Also, vacuum in the intake manifold creates a pumping loss, as the cyl comes down it has to overcome the pressure drop across the piston, the piston has to fight the vacuum it creates. Buy partially filling the cyl with egr, the vac drops, the pumping loss falls, and economy improves. Way back when criuse vacuum was used to help asses fuel economy, the more the merrier. Anyone remember those old vac gauges from jcwhitney that had the sticker over the numbers that told you fuel economy? (for those of you that don't know, jcwhitney was like THE ssautochrome back in the days of paper and pre internet) In fact many newer vehicles with variable cam timeing and drive by wire (I.E. the triton v-8 ford, cadilac v-6, and some bmw's) will retard the cams so much at cruise that the engine requires close to wot to maintain speed, this drops inlet vac and drops all the pumping losses. Basiccaly you detune the engine so its ve is very low and only makes the power (and therefore only burns the fuel) you need to cruise.

What I had mistakenly believed was that the fuel injection system was not affected directly by EGR controls. Thus, fuel would be set to inject based on metered and fresh air coming through the intake (not taking into account the recirculated air, which has very little oxygen remaining). Therefore, when the low oxygen exhaust gases replaced fresh charge, the fuel would be overkill due to the overall oxygen difference in the charge between what the ECU assumed it to be based on MAF output etc and what it really was because of the recirculated gas.

Anyways, I'm assuming now I was wrong to believe this, and that the fuel input is actually adjusted based on EGR to maintain the right A/F ratio for the actual amount of oxygen present. Is this right? I have never really looked at an EGR system in depth before and I don't really know how it interfaces with the car other than recirculating.



Right, so from my understanding, the presence of recirculated exhaust gas is to act as an extra reservoir for heat during combustion, thus bringing down the flame/overall temperature. Since NOx production increases with temperature, this process reduces the overall NOx production. I am thinking this is what you and others have just said .

I actually never thought about the pumping effect by EGR. Makes prefect sense now that you have mentioned it though, it's a cool idea.

As far as running rich, I never meant to say there was actual fuel leftover to be recirculated.. was referring to how it decomposes into hydrogen and CO, etc.. More what I meant was that not all of the exhaust species are in fact inert in the next burn.

You really seem to know the EGR well though.

My previous (and apparently somewhat wrong) post was simply speculation.

Good posts DMSentra and Fastspec2.

Now that makes sense why MPG's would drop with EGR gone.

I remember hearing that if your EGR is clogged up then you could possibly get crappy MPG's.

My brother's 99 Acura TL had the EGR clogged up, after I cleaned it up the car felt a little more powerful, dunno about MPG's though...

my mpg on my auto GA did go down a little (noticibly)
but on both of the sr20 5-speeds that i have had have stayed the same

Not sure if this is true, so don't quote me, but I thought that the original intended purpose of an EGR system is to burn any unburned fuel that snuck through the system the first time. Upon recirculating, it gets another shot at combustion. By removing the EGR, this fuel doesn't get a second chance and passes through unburned. So rather than saying that your MPG goes down upon removing the EGR, a more logical way to describe what's happening is that your GPM goes up if that makes any sense. Either way, it hurts efficiency, as the engineers of the EGR originally expected it to occur, but what they didn't take into account properly was the efficiency degradation from carbon buildup in the throttle bodies. And if you're wondering, I did remove the EGR from my car.

That makes sense too!

But the thing is, its only getting gas from Cyl #4, which has to go up into the egr hole...

This was discussed on the anti dash forum a while back. I don't know the link, but it came to a conclusion that it didn't increase performance or gas mileage. It was purely aesthetic and to solve some idle issues people might of had.

I think I remember seeing that thread...