OK - I never ever pay attention to jack until its something that I might be interested in. After reading BAMs thread on the hot cam install he is doing, it is becoming more attractive to me to get rid of the EGR and all the hardware associated with it. Plus I don't like having that crap going back into my intake and throttle body.

So, what has to be done? Block off the EGR holes on the back of the intake, remove the hardware and have Mick tune it out? Can I get rid of the air pump down in the corner of the bumper too?

What's the Cons of removing EGR? Any?

I am mister EGR after the fiasco I have been through with my headers. This is on an L98 but I think the info I got would be the same......maybe. From what I can gather you may run a bit hotter engine temps with out the cooling influence of the exhaust gasses but not enough to worry about. And somehow when you are under hard excelleration the EGR shuts off so you don't have that crap going into the cylinders at full throttle anyway.

Your check engine light will come on and that is what has to be programed out is what I have been told. other than that I don't think it makes any difference if you have the EGR or not.

It does clean up that side of the engine on my car and I like that! That is all I know about it.

I forgot to add that we do not have any emmision checks out here so I have elliminated both the EGR and the AIR but don't think that would effect the emmisions on a warmed up engine.........then agian more knowledgable folks may say that is not correct.

I found this on an earlier EGR post. I hope posting it again here is ok. I'll probably just keep mine in tact. I was just exploring because it would be nice to get rid of that crap!

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Posted by NCKid

EGR serves one purpose and one purpose only. That purpose is to reduce Oxides of Nitrogen (NOx). Under normal combustion, Nitrogen(N2)+Oxygen (O2) in the air and Hydrocarbons (HC) in the fuel combine into water (H2O) and Carbon dioxide (CO2) and the Nitrogen remains unchanged.

Under very hot combustion temperatures, the Nitrogen reacts with the other two byproducts and forms Nitrogen oxide (NO). After being released into the atmosphere, it picks up
another Oxygen and becomes Nitrogen dioxide (NO2). In the presence of sunlight, it combines with other compounds like Hydrocarbons and forms Smog. Since exhaust gas is inert (very stable) it doesn�t burn again. So by being introduced into the combustion chamber, it will lower combustion chamber temps enough so that the Nitrogen doesn�t react with the other compounds and is passed unchanged out the tailpipe thus not contributing to smog. Now, since exhaust gas doesn�t burn, it doesn�t exactly help with combustion. At higher RPM�s, this really isn�t noticable, but at idle, the reintroduction of exhaust gas will cause a very rough idle and can cause stalling if to much is introduced into the combustion chamber.

At WOT, EGR is not operational either, so you are getting the maximum out of the engine.


EGR Operation


Like mentioned before, EGR flow is good at higher RPMs, but not good at idle, so some sort of control needs to be place on the EGR system. Earlier systems used ported vacuum straight to the EGR valve. At idle, the throttle blades
are closed, so there isn�t any ported vacuum. When the throttle is opened, ported vacuum starts to build. The more throttle, the more ported vacuum. This is how
vacuum advance distributers work. As throttle is increased, the EGR valve opened further. Once the throttle is closed, ported vacuum is lost and the valve closed.

Most L98s (F and Y-body) use the basic diaphram EGR valve, but instead of relying on ported vacuum, it relies on vacuum that is allowed to pass through a solenoid.

The solenoid is controlled by the ECM. When conditions are right (I will give them later) the ECM will ground out the solenoid. The solenoid is a Pulse Width Modulated (PWM) meaning that the amount of vacuum is controled by the computer rapidly switching on and off to ground. The more vacuum the ECM wants to go to the EGR valve, the more time it lets the solenoid remains grounded, measured in Duty Cycle. With a scantool, you can command the EGR solenoid to
say 50% Duty Cycle and actualy feel the pulses if you put your finder over the vacuum port of the solenoid.




EGR Diagnostics


Now that you understand what EGR does and how it does it, lets see why sometimes it doesn�t do it. Since exhaust gas if being introduced into the intake manifold, things like manifold vacuum and airflow reduce slightly. Speed density computers can recognize EGR flow by looking for a drop in vacuum via the MAP sensor. (84, 90-93)

MAF systems use either a temperature switch mounted in the base of the valve or a diagnostic vacuum switch. Since exhaust gas is hotter than fresh air, it can pick up EGR flow by sudden increases in temp when the valve is open. The vacuum switch monitors vacuum going from the solenoid to the valve. In theory, if the valve is getting vacuum, then the system "should" be working. Highway speeds is when the most EGR flow is commanded. When cruising on the highway, the computer will pulse the EGR solenoid so that
vacuum will pass and go to the EGR valve. After commanding the solenoid on, it will look for signs that the EGR valve opened by one of the means mentioned above. If the ECM does not see the change its looking for, this is when the light comes on.
What are some possible causes of no exhaust flow?

Make sure that the solenoid is getting vacuum. A plugged or broken vacuum line will make everything else inoperative. If vacuum isn�t getting to the solenoid, it surely will not get to the EGR valve.

Make sure the ECM has control over the solenoid. Visually make sure that the connector is firmly seated into the solenoid and that the terminals inside the connector are not corroded or damaged. Usually you can rev the engine while it is in closed loop and it will be enough for the ECM to command EGR so you will be able to feel vacuum at the
solenoid. If you feel vacuum, than the ECM has control over the solenoid and adequate vacuum is reaching it. If you do not feel vacuum, you may need to drive the vehicle with a vacuum gauge hooked up to the solenoid. If you are driving in closed loop, you should see some vacuum. If you don�t the solenoid is probably bad, or the ECM is not controlling it (bad ECM grounds or ECM) providing you
had vacuum going to the solenoid. It is highly unlikely that you have a bad ECM, they rarely fail.

Inspect the vacuum line going to the EGR valve for plugging or being broken. It is not uncommon for previous owners to plug these vacuum lines with something to try and cure a �rough idle�. The lines can also become plugged with carbon deposits over time.

Check out the valve itself. Make sure it isn�t seized by manually lifting up on the diagphram. If it moves freely, put a vacuum on it. It should move and stay there (hold a vacuum). If it doesn�t move, try lifting a little on the diagphram, if it still doesn�t move, or wont hold vacuum, the valve is bad.

If everything still checks out OK, then the only other thing that will limit exhaust gas flow is plugged up passages in the intake manifold and cylinder head. This is a common problem with the V6�s and will leave many technicians scratching their head because the passages can�t be seen. Get a rifle cleaning brush and a shop vac and start cleaning.


Disabling EGR


Most people like to disable the EGR because they claim that hurts performance. In actuality, disabling the EGR can hurt performance.

As we already know, at certain thorttle postitions and RPMs, the ECM will command EGR operation. This is to cool combustion chamber temps under load.

Well, with cooler combustion chamber temps, we can further fuel economy by advancing the timing. We know that to much timing will cause �pinging�. But when we keep the combustion temps down, the timing can be advanced without the �pinging� effect. At highway speeds, the ECM commands EGR operation and will advance timing accordingly. With a blocked of EGR, the computer thinks it is flowing when it is not and will advance timing. Now that the combustion chamber temps are much hotter, the advanced timing is no longer a good idea and detonationoccurs. Since detonation can severly damage an engine, knock sensors are used.

When the knock sensor detects detonation, it will retard timing. It takes more to stop detonation that it does to cause it and this is where it hurts performance. For example, at highway speeds, your total advance may be, lets say 30* BTDC. If the computer advances it one more degree to 31* and it detects detonation, it can�t just go back to 30* to stop it, it must retard timing to like 25* to try and stop it, and if it still occurs it will further retard timing. If the EGR was working properly, the temps would have stayed cool enough to operate at 31* with no problems.

Now, if you ran into that problem of carbon plugging up the passages, and choose to disregard the above section, there are benefits to getting rid of the EGR totally.

First, you'll need to do the Diode Trick for the EGR, or have the Chip/PCM reprogrammed to take out Code 32 and EGR function, or you will get the SES light eventually. If its not during the startup check in the morning, you'll get it on the highway.

With EGR deleted, you'll no longer be injecting soot into your intake, which can plug up ports and get carbon stuck all over your valves. With a new engine I would not hesitate do get rid of it. If you have a race motor and are at WOT all the time, this wont be an issue since EGR is off at WOT. The clean internals you'll have are going to produce more power, for a longer duration than a street motor. Thats not to say a 110K mile 'vette cant put down its OEM numbers though.

Note about L98 vs LT1.

1985-1989 V8:

These systems use a typical EGR valve with one exception. There is a Diagnostic Temperature Sensor threaded into the base of the EGR Valve. Because these cars are equipped with a MASS Air Flow sensor, it uses this temp sensor to detect changes in temperature. Primarily, it is looking for a sudden rise in temperature when the EGR valve is opened. Everything is the same as mentioned above, with the addition of the temp sender. It is wired directly to the ECM, and serves as an EGR self diagnostic only. Some potential problems that would cause a code on these systems are: Ruptured EGR diaphragm, broken vacuum lines, defective or plugged EGR Solenoid, poor connections to the solenoid or diagnostic switch, or a failed diagnostic switch

LT1
These systems use the same EGR valve for the previous V8's, except the deletion of the Diagnostic Temp Sensor. Because these systems are Speed Density (using a MAP sensor) it can detect EGR operation in another way. Usually the EGR diagnostic is run on a long decell. When the vehicle is in decell, the EGR valve is closed. The ECM begins to monitor MAP sensor voltage very closely, and will cycle the EGR Solenoid to open the valve fully and then closed again and watch for the sudden changes in MAP sensor voltage, due to the introduction of exhaust gasses into the intake. Failures for these cars are similar to those on the previous V8's, except the temp sensor, since it is deleted.

With my 383 install I had the mechanic fabricate a block off plate and plugged upt the AIR tubes and removed the AIR pump.
On my tune I had them delete the EGR and AIR checks.
Actually my water temps are pretty good, have only seen 200 waiting on grid or after pulling off track. Oil temp is a little higher with max 220, I need to figure out an oil cooler setup next.

All of EGR tables are zeroed out in the bin as well as turning the "switches" off that set codes. The same would apply to any AIR with the exception of changing the 02 add-on.
When tuning several things change, getting the fuel and timing right controls detonation and or spark knock. When spark knock occurs it is not only a product of too little fuel but can sometimes occur from too much fuel (particularly in a map car). Where and how much timing is pulled is also controlled in the bin which are modified values. Once enough data is used to get the tune right, if encountering a weird load/rpm range typically the most timing I see being pulled is 1-3*. With SD/map cars it also important to note that it takes quite a bit more data to get the car tuned well. But the consistency level of fueling/timing/load values becomes excellent. IMO it can become a better tune than the maf cars due to the ability of having actual fuel and timing cells through-out the entire rpm vs load ranges. The SD bins are also more "hacked" (the ability for better tuning due to an increase in IAC controls, fueling in open, closed and pe etc.etc.)out than any of the maf bins. This is also one of the reason/s why it takes more work/time to develop the tune.

I disagree with the absolute statement that EGR only lowers NOx emissions. It does, no question, but it also lowers combustion temps, which helps reduce detonation.

I know the LT4 has a cam profile with a different LSA, so the EGR was removed; I am assuming the LT4 hot cam keeps that same LSA, meaning the EGR becomes redundant.

Fair enough... simply listen to Mick.

Very true, egr will reduce cylinder temps. in a more stock application, and was definitely part of the intent/design.

Some of the things I see are that with a more modified motor, especially bigger strokers and or using power-adders, cylinder pressure is increased. With that, the temp. will increase some at the heads (not the CTS/intake typical scan data).

This is controlled in several ways, because you're going to be making more tq./power in those ranges, timing doesn't need to be that tweaky anymore to get it have response/power etc. All hacks/bins have various add-ons tables for comping fueling, IAC, etc.(some for timing) based on temps. to further control changes that occur from motor/cyl. temps. When these are changed, this also aids in controlling temps. Additionally if it sequential, the fueling can also be tuned better. Obviously this doesn't help much if trying lug the car in 6th at very low speeds etc.

Mick you have forgotten more than I will ever know about this stuff. What is your rec on my stock L98 with headers and an AIR delete and EGR delete? Is that going to be hard to tune? How do we tune a 90 L98 from where you are at and where I am at? Thanks

Ultraman, PM sent.