Emissions
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Race Director
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From: WI
Emissions
I was learning more about the emissions. The AIR/smog pump injects fresh air to the exhaust valves to promote burning more gas. The EGR puts exhaust/unburned gas, back into the intake to get burned. Both these systems would help lower idle emissions to pass better. I don't know if the EGR works at idle, perhaps there is a tech tip to measure volts, to be able to tell? Also perhaps you could fashion a switch to turn the EGR on at idle for emissions testing or just have a EGR tube without a switch.
Le Mans Master
Joined: Jan 2003
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From: Portland Oregon
Originally Posted by Aardwolf
I was learning more about the emissions. The AIR/smog pump injects fresh air to the exhaust valves to promote burning more gas. The EGR puts exhaust/unburned gas, back into the intake to get burned. Both these systems would help lower idle emissions to pass better. I don't know if the EGR works at idle, perhaps there is a tech tip to measure volts, to be able to tell? Also perhaps you could fashion a switch to turn the EGR on at idle for emissions testing or just have a EGR tube without a switch.
Actually the AIR system in the newer cars inject fresh air into the exhaust stream to help the CATs to light off.
In most EGR equipped cars from say 96 and earlier, there was no electronic feedback for the EGR. Some trucks did use a electronic EGR valve with position feedback. Our C4s however did use a EGR solenoid which was modulated by the PCM. In older L98 cars it was used in conjunction with a EGR Temperature switch. The ECM got feedback from the temperature switch to indicate exhaust flow from the valve. No feed back means the ECM would set code 32. The temp switch is a constant thorn in the side of a L98 owner
The later LT1 cars that used a EGR used feedback from the MAP sensor. When it EGR is commanded on, the PCM knows that there is a pressure difference when its on or not. No DP means the EGR isn't working properly and then it sets a code. The LT4 engines didn't use a EGR valve because there was sufficient overlap in the LT4 cam to provide the same effect as the EGR valve.
Melting Slicks
Joined: May 2002
Posts: 2,670
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From: Severna Park MD
Originally Posted by tjwong
Actually the AIR system in the newer cars inject fresh air into the exhaust stream to help the CATs to light off.
In most EGR equipped cars from say 96 and earlier, there was no electronic feedback for the EGR. Some trucks did use a electronic EGR valve with position feedback. Our C4s however did use a EGR solenoid which was modulated by the PCM. In older L98 cars it was used in conjunction with a EGR Temperature switch. The ECM got feedback from the temperature switch to indicate exhaust flow from the valve. No feed back means the ECM would set code 32. The temp switch is a constant thorn in the side of a L98 owner
The later LT1 cars that used a EGR used feedback from the MAP sensor. When it EGR is commanded on, the PCM knows that there is a pressure difference when its on or not. No DP means the EGR isn't working properly and then it sets a code. The LT4 engines didn't use a EGR valve because there was sufficient overlap in the LT4 cam to provide the same effect as the EGR valve.
In most EGR equipped cars from say 96 and earlier, there was no electronic feedback for the EGR. Some trucks did use a electronic EGR valve with position feedback. Our C4s however did use a EGR solenoid which was modulated by the PCM. In older L98 cars it was used in conjunction with a EGR Temperature switch. The ECM got feedback from the temperature switch to indicate exhaust flow from the valve. No feed back means the ECM would set code 32. The temp switch is a constant thorn in the side of a L98 owner
The later LT1 cars that used a EGR used feedback from the MAP sensor. When it EGR is commanded on, the PCM knows that there is a pressure difference when its on or not. No DP means the EGR isn't working properly and then it sets a code. The LT4 engines didn't use a EGR valve because there was sufficient overlap in the LT4 cam to provide the same effect as the EGR valve.
The tuner I used turned off the EGR in the PCM so that it won't throw codes. I am getting parts to do so, but I have not yet yanked the EGR plumbing or the EGR valve. I am running the LT4 hotcam in a modded LT1 so I should have sufficient overlap to provide natural EGR like a stock LT4. Is my understanding correct?
Does the EGR become effective at idle when the engine is warm, or is it only at running speeds that the EGR is turned on by the PCM. There is a vacuum signal to the EGR that I haven't yet touched so EGR would be functional if the PCM was only monitoring, and not commanding. Am I out in left field? Is the EGR turn off at the PCM causing my high HC readings, or are HCs unrelated?
I know that's a lot of questions, but the manual isn't helping me understand this.
Car is a 94.
Le Mans Master
Joined: Jan 2003
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From: Portland Oregon
Originally Posted by FELNGR8
I'm unsure what is up with the EGR. I thought EGR primarily affected NOX, which in my case was not tested (all N/A on the sheet) .
The tuner I used turned off the EGR in the PCM so that it won't throw codes. I am getting parts to do so, but I have not yet yanked the EGR plumbing or the EGR valve. I am running the LT4 hotcam in a modded LT1 so I should have sufficient overlap to provide natural EGR like a stock LT4. Is my understanding correct?
Does the EGR become effective at idle when the engine is warm, or is it only at running speeds that the EGR is turned on by the PCM. There is a vacuum signal to the EGR that I haven't yet touched so EGR would be functional if the PCM was only monitoring, and not commanding. Am I out in left field? Is the EGR turn off at the PCM causing my high HC readings, or are HCs unrelated?
I know that's a lot of questions, but the manual isn't helping me understand this.
Car is a 94.
The tuner I used turned off the EGR in the PCM so that it won't throw codes. I am getting parts to do so, but I have not yet yanked the EGR plumbing or the EGR valve. I am running the LT4 hotcam in a modded LT1 so I should have sufficient overlap to provide natural EGR like a stock LT4. Is my understanding correct?
Does the EGR become effective at idle when the engine is warm, or is it only at running speeds that the EGR is turned on by the PCM. There is a vacuum signal to the EGR that I haven't yet touched so EGR would be functional if the PCM was only monitoring, and not commanding. Am I out in left field? Is the EGR turn off at the PCM causing my high HC readings, or are HCs unrelated?
I know that's a lot of questions, but the manual isn't helping me understand this.
Car is a 94.
Team Owner
Joined: Sep 2001
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
EGR functions when the coolant reaches 170 and youre at less than 70% throttle, but I'm unsure of the lower limit.
It doesn't function at idle though. Its vacuum will cause a poor idle if they its not sealed though.
AIR continues to function after the car is hot, but to a lesser extent as its main purpose is to get the cats cooking.
It doesn't function at idle though. Its vacuum will cause a poor idle if they its not sealed though.
AIR continues to function after the car is hot, but to a lesser extent as its main purpose is to get the cats cooking.
Melting Slicks
Joined: May 2002
Posts: 2,670
Likes: 4
From: Severna Park MD
Originally Posted by tjwong
Your EGR valve is only commanded on during cruise conditions and never on idle. It is only on after a temperature threshold is met. If there is a vacuum signal at the EGR at idle and if the EGR opens it can cause high HCs. This is because the gas flow will cause a slight lean condition and the O2 sensors will report this, which in turn will cause the PCM to richen the mixture to correct the lean condition. Try disconnect the EGR valves vacuum hose and see if the idle changes.
My idle was bumped to 950 by John Sealock to get better vacuum at idle. Related? All the tuning changes I have were done after my last successful emissions test 2 years ago.
