EGR Mod

varmint2506 · November 12, 2002

I see a few folks have made EGR mod's. What kind of mod's are being done? Just curious.

I had always found (older models) the EGR blank off kills the mileage and doesn't do much for the power.

MiSdIrEcTeD_1 · November 12, 2002

I did it at the same time I installed my TB spacer and induction... Cant hurt anything, but doubtful youre gonna notice 1/2HP.. lol

CLICK HERE

CMNTMXR81 · November 13, 2002

It is a mod that completely blocks off EGR flow, therefore not allowing hot air from flowing back into the intake therefore heating the incoming outside air charge a little.

However, throttle tip in and light to mid throttle applications aren't as smooth as well as economy suffers when it is completely blocked off because some of that hot air being re-routed back into the intake still has unburned fuel in it, therefore essentially enriching the fresh a/f without having to physically add more fuel. This method of leaning it out can result in knock retard which leads to that poor driveability.

The best way to do it if you're gonna do it would be to use a block off plate with a considerably smaller hole drilled in it to let some EGR gasses still get past but no where near as much as the stock setup.

At WOT however, the EGR system is turned off anyway, therefore having no affect on any performance and as such won't add a measurable amount of HP.

In the end, all you're doing is hurting light to mid throttle driveability and you aren't making serious power at this point anyway

varmint2506 · November 13, 2002

CMNT,

I was looking at this for the '98. What will I expect to see from the OBD II.

CMNTMXR81 · November 13, 2002

You can do it 1 of two ways, manually block it off with a plate between the EGR inlet tube and your intake or turn the EGR pump off in the PCM with something like LS1Edit.

Either way you do it, drive around and at quick throttle tip in, you should now notice some ping momentarily until the injectors catch up and drop more fuel in. Having a scanner like AutoTap is also helpful as you can watch knock retard during that quick throttle tip in as well as selecting the EGR on/off if you leave the EGR turned on in the PCM. You can monitor when the EGR pump turns on and off when this is selected.

However though, at full tilt, the EGR system is shut off by the PCM itself, so it has no (or minimal) bearing on performance numbers.

You can also turn off the EGR pump in the PCM

CMNTMXR81 · November 13, 2002

I forgot to add that some people completely remove all their EGR equipment when the turn off the EGR in their PCM to save weight and then block off the EGR feed from the headers.

varmint2506 · November 13, 2002

Don't have the software or hardware to connect a PC. So... I guess I will tinker aroud with a block off plate. :thumb:

CMNTMXR81 · November 14, 2002

Go for it. :thumb:

I'd block it off (or make a smaller hole'd block off plate) and put it where it's fed off the exhaust manifold.

mnstrmdnss · November 14, 2002

does anyone even know what the EGR system actually does?

you are all trying to remove emissions equipment and you dont even know why it was put their in the first place or what it does!

CMNTMXR81 · November 14, 2002

EGR stands for Exhaust Gas Recirculation. What it does is their is still s slight bit of unburned fuel in the exhaust leaving the engine pre cat. There is a tube usually off the headers that routes some of this gas up to a pump. Upon certain conditions this pump is triggered on and therefore injects that gas back into the intake stream.

The certain conditions that generate this are generally light to mid throttle applications as well as throttle tip in as I've mentioned above. Essentially when you quickly tip your throttle in, the incoming air charge speeds up quicker than the PCM can adjust and have the injectors inject more fuel. This temporary conidtion (which usually lasts only a second or two in most cases, can lead to a temporary lean condition therefore resulting in knock and rough driveability. To eliminate this, the EGR pump is already injecting a slightly rich (because of the slight presence of unburned fuel) charge back into the intake to help richen thinggs up a little until the injectors catch up and our on their game.

During light to mid throttle constantly changing throttle conditions it is very similar to the above situation with throttle tip in. The pump is there making up for the injection system.

At WOT the PCM automatically shuts off the EGR pump because the PCM is sending a maximum signal now to the injectors and they are shooting as much as they can per their fuel tables in the PCM.

That's it in a nutshell. It helps in efficiency because it re-routes some of that unburned fuel to be re-burned again as well as helping in emissions for the same reason. It helps smoothen out driveability and makes the engine more friendly in the driving conditions I mentioned.

There are ways around it though, as the C5 to present and now '02 F-Bodies incorporate an EGR less system. However they get away with it due to the ramp profiles on their camshaft. It's not an uncommon mod for 98-01 LS1 F-Body guys to either block off or remove their EGR pump when upgrading to the LS6 intake as the LS6 intake stock has no EGR provision. They then turn off the EGR in their PCM so as to eliminate an SES code.

They do it (and the reason behind it) is to eliminate that hot charge as it is exhaust circulating with the nice cool air just being sucked in through your air airbox and MAF. I think many of these people don't realize that it doesn't have any affect at WOT throttle anyway, so what's the point other than hurting driveability in normal driving (I.E. Non racing) situtations.

TahoeSS · November 16, 2002

I agree-

There is no cheap way to get Real HP gains.

Everything has to work together ;computer controlled or not.

mnstrmdnss · November 17, 2002

hey, cmntmxr81, where are you getting your information? an EGR system uses exhaust gases to lower the oxygen content entering combustion chamber to reduce combustion temps to reduce NOX (oxides of nitrogen). EGR simply reduces NOX output. thats it. it has nothing to do with increasing gas mileage. nothing. im not trying to start something, but like i said before, people shouldnt be messing with stuff or removing it if they dont know what it is or how it really works.

CMNTMXR81 · November 19, 2002

I agree people should'nt be messing with it.

Personal experience is where I got my information from. With my multiple PCM tuning woes with Ed Wrong. He turned my EGR off in the PCM without me telling him too. My gas mileage suffered by about 2-3mpg. When I found it was off and turned it back on with a TechII, I saw that gas mileage come back right away.

CMNTMXR81 · November 20, 2002

Well, now that I have a few extra minutes to explain what was happening, I will.

When the EGR was turned off per Ed Wright, at moderate starting acceleration from a dead start, I'd get 30-35 degrees of initial timing. Due to the lean condition, I'd also get the accompanying 14-18 degrees of KR instantaneously resulting in My net timing being in the high teens. This made starting the car rolling was a little more difficult. In order to compensate, I'd simply ride the gas harder. I.E., bringing the RPM's up to 2500-3000rpm and riding the clutch out until the car was sufficiently rolling to eliminate this hesitation. Now simple physics tells me, that depressing the gas more to compensate equals more gas injected into the engine, therefore less in the tank, therefore requiring me to fill up a tad more often. Hence, my economy suffered due to the terrible drivability of the car.

Conversely after I turned the EGR back on, I got the same amounts of initial timing, and .2 - .4 degrees of KR netting me high to mid 30's of timing. Car accelerated much smoother and I could start the car from a dead stop with much more ease. I only need to bring RPM's up to 1,200 - 1,500 (if at that) to move the car and it doesn't chug and thug like it did before. I also don't need to ride the clutch out like I was before.

The same would happen on the highway where I'd want to gradually accelerate. I'd experience the same timing woes as above due to the lean condition and in order to compensate, I'd simply hammer the gas harder. More gas = less fuel economy. After turning the EGR back on, driveability came back, and I could accelerate like normal.

I hope that helps clarify things a little. Now do you see where economy suffers? I figure with automatic transmission equipped trucks, it'd affect it a tad more.