Increasing EGR flow for better mileage

[ConnClark]

EGR double edged sword. It can help and it can hurt. Decrease intake manifold vacuum (good for reducing pumping losses) and you decreases crankcase vacuum (bad for reducing pumping losses).

Autospeed did some articles on EGR and modifying EGR.

EGR Come Back
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Modifying EGR part 1
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Modifying EGR part 2
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They claim that it improved mileage by 3% in town and saw no gain on the highway. However I don't consider this a significant improvement to state for a fact that they really did improve things due to wide variance of in town traffic.

Your car computers probably are already close to the optimum for EGR adjustment.

[MetroMPG]

Originally Posted by ConnClark

Your car computers probably are already close to the optimum for EGR adjustment.

Since "driveability" is one of the considerations the engineers must take into account for setting EGR levels, I doubt that's true. (IE, not optimal, from a fuel economy perspective).

[Daox]

As I recall from that article, the Insight really doesn't use EGR that often at all. In steady state cruise it isn't used at all. I'm guessing it is only used during moderate engine loads during acceleration. Its kind of a different beast than a normal ICE being that its hybrid, lean burn, and uses EGR.

Edit: I found the quote.

In lean cruise, the Insight’s EGR valve is closed. At idle and under full throttle, the valve is also closed. In fact, in normal driving it is closed far more often than it is open. So when is it open? The valve is open its greatest amount (about 50 per cent duty cycle) at light and moderate throttle, at both low and high revs. It also opens when the car drops out of lean cruise to consume its stored NOx emissions (see Giving the Insight a Good Driver for more on the lean cruise behaviour of this car). Finally, it is open for a short time on throttle lifts.

[MetroMPG]

A relatively simple way to test the effect of diluting the intake charge to mimic EGR (without actually going through the process of modding it) would be to get a bottle of some inert gas (CO2?... what gas do MIG welders use?) and feed the intake through a tube.

[Ford Man]

EGR flow can definitely have an impact on FE. I bought a new Buick Regal in 1977 and when I first bought it, it had a flat spot during acceleration and was only getting about 12 mpg. One day I was at the dealership where I bought the car and I told the salesman about the flat spot and that I wanted it fixed, so he took the vacuum line to the egr valve off and stuck an eraser from a mechanical pencil in it and put it back on stopping the vacuum from opening the egr valve. From that time on it didn't have the flat spot and the gas mileage increased to about 15-16 mpg. I haven't tried it on a car since, but when the weather warms up and I get a base line mileage I might try plugging the line on my '88 Escort for a few tanks to see what the results are.

[Coyote X]

The metro EGR system would be reasonably easy to bypass without having the computer throw a fit about it on OBDII cars, OBDI could be bypassed using the following method without the computer caring at all.

If you look on the intake manifold drivers side there is the EGR valve. Follow the hose from it to a round thing with another thing right under it with some wires that is clipped in a holder right beside the valve cover. That is the controller that uses a PWM signal to regulate the valve opening. From there the hose runs to the throttle body.

To make it run full on just take the hose from the EGR and run it straight to the throttle body leaving the PWM valve hooked up to the wiring. The computer will be more or less happy and still think it is controlling it. At least until you get a O2 sensor error or cat converter out of range error after a few hours. But at least for a simple A-B-A type of test that is all it would take. If any useful data comes out of that then trying to figure out how to permanently modify it would be worth looking into.

I don't have enough of a working EGR system left to test it out on my car so I guess this is something someone else will have to test.

[Daox]

I think we should get an idea of how much EGR flow we are looking at for doing something like this. I'm going to use a 1.5L engine example because that is what is in the Paseo and thats likely what I'll be doing testing on. Please correct me if you see any errors in my methods here.

The at 55mph, the Paseo is geared to be at 2600 rpm. At 2600 rpm and WOT, we are looking at the engine sucking in around 60 CFM (assuming 85% volumetric efficiency).

Now, from reading I've heard that a 40% EGR mixture is the absolute maximum that an engine can handle before misfires occur and things start to go downhill. Darin thinks he read that it is more like 20%. So, I'm going to go with the lesser of the two just to be on the safe side. Again, feel free to add any info/corrections.

20% of 60 is 12 CFM at highway cruising speeds. 40% would simply be double that, 24 CFM.

12 CFM doesn't sound like a ton to me. This is probably good because I pulled the EGR valve off the 96 Paseo I have and the hole going from the exhaust side to the valve is pretty tiny. I didn't clean it all up yet, but it looked to be around 3/16" (5mm) or so. There is no way that an orifice that small can pull 12 CFM through it without some pretty hefty pressure drop. So, it looks like the stock sided EGR valve is going to be undersized. I'm also going to assume this is similar for most vehicles out there. I sure would be nice to know what the stock EGR systems are designed to flow.

[MetroMPG]

Here's another decent EGR reference:

Understanding exhaust gas recirculation systems

Understanding Exhaust Gas Recirculation Systems

A well-designed system will actually increase engine performance and economy. Why? As the combustion chamber temperature is reduced, engine detonation potential is also reduced. This factor enabled the software engineers to write a more aggressive timing advance curve into the spark timing program. If the EGR valve is not flowing, onboard diagnostics (OBD) systems will set a code and the power control module (PCM) will use a backup timing curve that has less advance to prevent engine ping. Less timing advance means less performance and economy.

[Daox]

Originally Posted by Ford Man

EGR flow can definitely have an impact on FE. I bought a new Buick Regal in 1977 and when I first bought it, it had a flat spot during acceleration and was only getting about 12 mpg. One day I was at the dealership where I bought the car and I told the salesman about the flat spot and that I wanted it fixed, so he took the vacuum line to the egr valve off and stuck an eraser from a mechanical pencil in it and put it back on stopping the vacuum from opening the egr valve. From that time on it didn't have the flat spot and the gas mileage increased to about 15-16 mpg. I haven't tried it on a car since, but when the weather warms up and I get a base line mileage I might try plugging the line on my '88 Escort for a few tanks to see what the results are.

That is very likely because the EGR system was not working properly in the first place. When an engine enables EGR it has to alter ignition timing. If the EGR system is clogged (which is common because it is a dirty system), the ECU will enable EGR, alter timing, and since it isn't working properly you'll loose power. A better bet for you would be to remove the EGR valve and plumbing, clean it out, and reinstall it.

[MetroMPG]

Originally Posted by Daox

I've heard that a 40% EGR mixture is the absolute maximum that an engine can handle before misfires occur and things start to go downhill. Darin thinks he read that it is more like 20%.

20 percent-ish.

I found my source for that figure, which is itself a quote of some kind of edumacational book:

Air induction, EGR, and fuel economy (John De Armond; Bob Hale)

I looked up your reference (Internal Combustion Engine Fundamentals, Heywood, page 837,838). Very interesting. Appears from his chart that BSFC minimizes at about 25% EGR.

It should be pointed out that the chart in question shows large gains for fast burn chamber designs. On the same chart is a line for slow
burn chambers that shows much less improvements and then only at
low (5-10%) EGR injection.

Anybody else other than me having a GS flashback?