I talk to a guy last night that said that the air pump takes exhaust from the cat and pumps it back into the manifolds. I cannot see why they would do that. I thought it take outside air and injects it into those 2 places? I am probly wrong though. If the first is the case, why did I remove the manifold tubes and leave the cat one on? Just thought I would ask. I was curiouse as to what it did anyway.

 

I'm pretty sure you are correct. It injects air into the cat or the manifolds, I think it depends on open/closed loop.

 

I copied and pasted this from Random Tech's website.

"Most converters produced in recent years contain two monolith "bricks" spaced several inches apart from each other. The washcoat on the forward brick typically contains rhodium which causes nitrogen oxides to break down into nitrogen and oxygen. After passing through the first brick, exhaust gasses pass through an air chamber before entering the second brick. In some converters, known as “oxidation” types, a small tube passes through the chamber and injects air pumped in by an engine-driven “smog pump”. (In some vehicles, the "smog pump" incorporates an electric motor, which reduces accessory drive complexity and also allows for remote mounting.) Injected air simply brings additional oxygen into the exhaust stream to assist in the oxidation process.

Although “three-way plus oxidation” type converters were prevalent during the 80s, that’s no longer the case. With improvements in washcoat technology, and improved control of air/fuel ratios, the need for additional oxygen has been eliminated. Some vehicle manufacturers have continued to use oxidation converters on some models, but typically that has been done to use up inventory. As an example, the Corvette and Camaro Z/28 were equipped with oxidation converters through 1991 and 1992 respectively. But when the LT1 engine replaced the L98 (1992 in Corvette, 1993 in Camaro) three-way converters with no air tubes were incorporated.


That should help a lot of people understand the reason for them.

It also sounds to me that if you use a newer style 3 way converter, then there should be no use for the A.I.R. pump anymore, right?

BTW, here's the link to the website.
Random Technology

AJ

 

I also thought that the air injection helped heat up the cat faster and the cat only effectively cleans the exhaust when its fully heated up.

 

mine is a little different.. the pump only goes to the exhaust manifolds.. one on each side.. I believe cyl 1 & 2

 

The A.I.R. pump also will be used to inject ambient air into the exhaust manifolds to aid in the heating up of the O2 sensor(s) and the catalytic converter itself during cold starts to lower the emissions levels during those cold starts. Emissions are the worst for a car (well... HC levels anyways) during cold startups and injecting oxygen into the exhaust manfiolds helps burn up some of those unburned hydrocarbons (fuel).

 

Yeah all of the TBI trucks were like that until '94 or somethin like that so yes, yours is different

 

Yes, I forgot about the exhaust manifolds. Thanx.

Where did you read about the "heating up of the O2 sensor(s) and the catalytic converter itself during cold starts" part?

I thought that was what a 3 wire O2 sensor was for? I mean (no flame, OK?) how can pumping straight, cool air (compared to the exhaust heat) help heat up the O2? Or the cat? It just doesn't make sense?

I did a lot of reshearch on this topic when nobody seemed to give me a straight answer when I asked the reason it was at the manifold.

Here's another location (Autosite Garage;Exaust) that I found about the purpose of the AIR pump.

Here's the script;

A switching system directs air injection to the exhaust manifold during warm-up to help burn the inordinate amount of HC and CO that's produced in that mode, then shifts it to the middle of the converter once normal operating temperature is reached (that's when NOx production begins) and the system enters closed loop.


Now when it says "in that mode", it means open loop when the A/F ratio is ~13.4:1 which aids in starting and continious running.

I am just wondering about the "heating up of the O2......." so that if you can lead me to where I can learn more, I will go and find and learn. And I like to learn. Just wish I liked it when I was in school!!!!!

I can tell you to go to that site anyway. It's pretty educational for those little Q's that you have, but maybe to scared to ask. For instance "What causes a cat to become blocked?" or "How can I check if my cat is clogged, or becoming clogged?"or even, "Why does my car hesitate when I step on the gas to really go?"

Some of these things I thought I knew the answer to, like the hesitation Q, but then I read that, and thought "That would cause hesitation." Like running to rich? I knew (or though I did) that a lean condition caused it, but just never though about the other end of the spectrum.

Here's the home page.

Autosite Garage

AJ

 

I know that intoducing oxygen into exhaust gases will cause it to heat up. I never heard of it being used to heat the 02 sensor up, but that does make sense. The mag Street Rodder had a giveaway car that had a leaky collector gasket, so they put an air pump on the car to heat up the exhaust and cause the gaskets to expand.

 

Where are you guys reading/learning this?

I thought the purpose of having an EGR is to do what you are saying. An EGR takes wasted gas from the exh. ports are redirects it into the intake to help warm up the intake charge & to make use of the unburnt fuel.

The AIR takes fresh air from the intake passages, and routes it straight to the exhaust manifolds/cat. I don't see how that's going to heat up the exhaust. It puts fresh, cool, more dense air into the exhaust system. I've read that it also helps keep the cat from getting too hot. That way the internals of the of the cat live longer and don't break down under extreme heat.

Plus, the amount of oxygen in the Earth's atmosphere is only about 20% of the contents of the air that we breath, or that our cars breathe. And this would be enough to cause the unburnt fuel in the exhaust manifolds to complete combustion at a higher temp? Is that how it works? I know that oxygen causes things to burn faster, but it is not a flammable gas. I just creates an environment that promotes faster burning. But I guess faster would need to be hotter.

I guess that makes sense now. Kinda relates to how nitrogen- oxide works (ie, Nitrous) in our cars. It would make sense the the purpose of the two parts nitrogen is to keep the air cool (and of course, more dense), while the one part of oxygen promotes burning.

HUH? Thanks to you guys, I think I got it figured out. And explained something else to myself also.

I dunno. I wish GM had a web page that explained their reasons for doing certain things at certain times. It would help us out a lot. After all, Ford does that kinda stuff. Why can't the General?

It's starting to make more sense now though, I think.

Thanks again,
AJ

 

Ummm.... Well you're kinda right, but a bit off on some of it.

The EGR valve introduces inert exhaust into the intake charge to lessen the amount of cumbustible gasses that mix with the fuel injected into the cylinder. This basically dilutes the mixture and makes it less volitile which lessens the chances of pre-ignition or ignition knock. The overall outcome of the EGR valve operation, and its main purpose, is to lower the temperature of the cumbustion process itself which lowers the amount of oxides of Nitrogen (NOx) gasses that the engine will emit which is one of the harmful emissions of an internal cumbustion engine when it operates at extremely high temperatures. The EGR really has nothing to do with burning up any unburnt fuel from the cumbustion process itself.

Now the A.I.R. system has a couple of purposes and one of them was posted above and deals with a three way catalytic converter. The other purpose of the system is what I stated. The main benefit of this system in it's operation regarding the pumping of ambient air into the manifolds, is for it to burn up some of the unburnt Hydrocarbons left over after the cumbustion process since the internal cumbustion engine is not 100% efficient. The A.I.R. system takes its air from the outside atmosphere and pumps it into the manifolds where the oxygen reacts with the extremely high temperature mixture of exhaust gasses and unburnt HCs and ignites some of those HCs. This basically lowers the HC output of the engine (and CO in a round about manner) which is another of the harmful emissions that an internal cumbustion engine emits.

Now the reason I say that the other purpose or benefit of the A.I.R. system burning unburnt HCs in the manifolds is to heat up the O2 sensor(s) and the catalytic converter, is this: Everyone knows that the engine management system will run the engine on a pre-set routine (open loop) during a start up and then transition into a flexible routine (closed loop) when the system receives enough reasonabley correct information from the O2 sensor. And closed loop is a much more efficient routine that yields better driveability and lower emissions. Now the O2 sensor(s) needs to reach a certain temperature before it will be able to accurately read the Oxygen content of the exhaust gasses. So the faster the O2 sensor heats up, the faster the engine gets into closed loop, the better the engine management system can control the engine, the better the driveability of the car is, and the better (cleaner) the emissions of the engine will be. The same can be said about the operation of the catalytic converter in that it is not able to operate very successfully in lowering the harmful emissions output of an engine until it too reaches a certain high enough temperature to perform as a catalyst.

All of this information can be found in a quality service manual. I know for a fact that every GM Service Manual will break down the operation of every single componant of it's respective car/engine/trans.

EDIT: Oh, and as for where I have learned/read this, I worked for three years at a Chevrolet dealer and have an AAS degree in Automotive Technology in additon to being a certified GM Tech. I graduated from a program called ASEP (Automotive Service Educational Program) which is a GM sponsered program for people wanting to become Service Technicians at dealerships.

Hope that helps some.
Good Luck!!

 

Side effect of my leaking exhaust, related to AIR pump:

Since I'm leaking at the manifold gasket on the back 2 cyls. on the drivers side (fixing soon) I get a VERY lound HISSSSS while the car is warming up due to the high pressure air leaking out. I've actually opened the hood during warm up on a REALLY cold day and watched steam puff from between my head and manifold! Not good!