What is the air pump really doing
Thread Starter
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
What is the air pump really doing
Now as I am tearing into the top end I had to remove pump, etc. My original plan was to use egr etc, as time went, couldnt get a new SR(accell redesigning), got tired of waiting and I changed the plan, the new intake has no egr, no problem, but I did get 2149's. At this point I can't see any reason to keep this "stuff" (air pump etc.).
If I buy a air pump delete aside from cosmetics, and eliminating, hoses etc. what am I really changing in the system, is that then have an effect a/f , 02 sensor, computer, the tune in the chip etc. (SD system 1990) TIA Mick
If I buy a air pump delete aside from cosmetics, and eliminating, hoses etc. what am I really changing in the system, is that then have an effect a/f , 02 sensor, computer, the tune in the chip etc. (SD system 1990) TIA Mick
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Before the ECM goes into closed loop, the air is directed into the exhaust manifolds to supply oxygen to the exhaust gases so they can keep burning. The gases burning in the manifolds help heat the O2 and gets the O2 "lit off" more quickly so the ECM can go from open to closed loop sooner. During closed loop the air is directed to the cat to aid in it's function. Of course this is all explained in your FSM.
RACE ON!!!
RACE ON!!!
Thread Starter
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Originally Posted by CFI-EFI
Before the ECM goes into closed loop, the air is directed into the exhaust manifolds to supply oxygen to the exhaust gases so they can keep burning. The gases burning in the manifolds help heat the O2 and gets the O2 "lit off" more quickly so the ECM can go from open to closed loop sooner. During closed loop the air is directed to the cat to aid in it's function. Of course this is all explained in your FSM.
RACE ON!!!
RACE ON!!!
Alright please bare with me in understanding this better. Through reading, my undersanding is that if no air oxygen enters the exhaust at the port, hc and co levels get to high, and then if air flows all the time it can increase cat temp.
If I delete the AIR then, and since the ECM controls function, does it "try" to adjust these readings through some other method if it can't find the AIR. And if it does, what does it try to adjust when no air readings are located from EDV(I believe).
In effect then to remove the AIR, I would really then need to delete it from the ECM aside from the plumbing itself. Would this be correct? M7
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
On a '90 the AIR control is an open loop function, i.e. the ECM has no feedback so it does not "know" if the AIR devices are present or not.
Indeed the burning of the rich mixture during warm up is aided by the air injected into the exhaust headers. However, the ECM needs three items before it will go closed loop after startup:
-a certain time elpased (??)
-coolant temp above 150deg F
-O2 sensor at operating temp and operting properly
So far as actually reducing polutants, remember that modern 3-stage cats are a huge improvement over 80s & early 90s technology. I seriously doubt that removing the AIR injection from a well tuned L98 with modern cats will markedly effect emisisons.
For a little exta boost, I've considered doing the AIR pump delete and just moving the AIR pump up front and power it electrically, as per the LT1 powered C4s.
Indeed the burning of the rich mixture during warm up is aided by the air injected into the exhaust headers. However, the ECM needs three items before it will go closed loop after startup:
-a certain time elpased (??)
-coolant temp above 150deg F
-O2 sensor at operating temp and operting properly
So far as actually reducing polutants, remember that modern 3-stage cats are a huge improvement over 80s & early 90s technology. I seriously doubt that removing the AIR injection from a well tuned L98 with modern cats will markedly effect emisisons.
For a little exta boost, I've considered doing the AIR pump delete and just moving the AIR pump up front and power it electrically, as per the LT1 powered C4s.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Don't know of any C4's without a 3 way cat - unless it's been removed - they all came from the factory with one.
Don't know of any modern fuel injected motor running without an air pump either. Granted the technology has switched to where it's spun by an electric motor rather than as an accessory drive, but it's still there, helping to get things nice and toasty.
Removing EGR without something to compensate to keep combustion temps down will decrease performance. You can try water injection - worked for the Brits in WW2 - or swap the cam out for a little more overlap. How much more you need is best determined with equipment most of us don't have access too - burning up your motor trying to find out what works is a poor alternative.
Don't know of any modern fuel injected motor running without an air pump either. Granted the technology has switched to where it's spun by an electric motor rather than as an accessory drive, but it's still there, helping to get things nice and toasty.
Removing EGR without something to compensate to keep combustion temps down will decrease performance. You can try water injection - worked for the Brits in WW2 - or swap the cam out for a little more overlap. How much more you need is best determined with equipment most of us don't have access too - burning up your motor trying to find out what works is a poor alternative.
Thread Starter
Le Mans Master
Joined: Feb 2005
Posts: 5,146
Likes: 3
From: The Motor City
Originally Posted by 65Z01
On a '90 the AIR control is an open loop function, i.e. the ECM has no feedback so it does not "know" if the AIR devices are present or not.
Indeed the burning of the rich mixture during warm up is aided by the air injected into the exhaust headers. However, the ECM needs three items before it will go closed loop after startup:
-a certain time elpased (??)
-coolant temp above 150deg F
-O2 sensor at operating temp and operting properly
So far as actually reducing polutants, remember that modern 3-stage cats are a huge improvement over 80s & early 90s technology. I seriously doubt that removing the AIR injection from a well tuned L98 with modern cats will markedly effect emisisons.
For a little exta boost, I've considered doing the AIR pump delete and just moving the AIR pump up front and power it electrically, as per the LT1 powered C4s.
Indeed the burning of the rich mixture during warm up is aided by the air injected into the exhaust headers. However, the ECM needs three items before it will go closed loop after startup:
-a certain time elpased (??)
-coolant temp above 150deg F
-O2 sensor at operating temp and operting properly
So far as actually reducing polutants, remember that modern 3-stage cats are a huge improvement over 80s & early 90s technology. I seriously doubt that removing the AIR injection from a well tuned L98 with modern cats will markedly effect emisisons.
For a little exta boost, I've considered doing the AIR pump delete and just moving the AIR pump up front and power it electrically, as per the LT1 powered C4s.
Didn't know about the 02 sensor as other variable. I thought the ECM actually operated the EDV solonoid.
Sorry about the questions that I'm sure many have heard before, but I am trying to understand the function a little more, other than just buying a kit a plugging lines.
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Buy a kit and plug the lines, it wont hurt a thing. The car will pass a sniffer when warm, so I see no grievous harm coming to anything.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Well I could be a little high with that 150deg mark. I believe you have seen the EPROM tables (I have not) so sounds good.
Though the AIR pump runs all the time the ECM uses the diverter to direct air flow into the exhaust manifolds until it goes closed loop mode, then it directs the air into the main cat. I understand that under certain conditions, like going to WOT, it just dumps the air to the outside.
My understanding is that the early cats were single stage, though the later L98s used three cats in the exhaust. This is why a modern 3-stage main cat is 48 state legal replacement for the stock 3-cat L98 system.
But, as mentioned, it should not have a real effect on environment nor emissions on a well tuned engine to eliminate the AIR system.
Though the AIR pump runs all the time the ECM uses the diverter to direct air flow into the exhaust manifolds until it goes closed loop mode, then it directs the air into the main cat. I understand that under certain conditions, like going to WOT, it just dumps the air to the outside.
My understanding is that the early cats were single stage, though the later L98s used three cats in the exhaust. This is why a modern 3-stage main cat is 48 state legal replacement for the stock 3-cat L98 system.
But, as mentioned, it should not have a real effect on environment nor emissions on a well tuned engine to eliminate the AIR system.
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
The programmed temp requirement did change slightly within the years, the one I have seen is at 146F.
The timers are not exactly the same length on all models either.
The timers are not exactly the same length on all models either.
