L98 AIR Pump air flow
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Instructor
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L98 AIR Pump air flow
I have an 87 which the previous owner removed the catalytic converter for a custom dual exhaust. He left the smog equipment in place including the metal line that would feed air to the cat. I'm not ready to remove the smog equipment, in fact I'm trying to restore the car to original to the best extent possible. There is an air escape that the system will dump air through on the front of the engine through a muffler. My problem is the when the system tries to blow air to the cat, it makes a loud sound because the tube has no muffler. Is there a way to make the system always dump the air to the front release outlet rather than back to the cat? Hopefully this description makes sense.
Burning Brakes
Joined: Nov 2004
Posts: 1,193
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From: Hillsborough NC
I would suggest checking the Factory Service Manual for this year. I have an 86 and was just doing some reading on this topic (for different reasons).
There are two diverter valves which control airflow in the system. These valves (front of engine with two electrical and several vacuum line connections) route the air from the pump to one of three places;
Out the muffler on the front of the engine
Into the exhaust manifolds
Into the catalytic converter
You may be able to apply voltage to force the system to do what you want, but again, you should check the FSM before you start applying current.
The Air Injection Pump is a continuous flow vane pump, it will pump air at all times while it is in motion. YOU SHOULD NOT plug the line to the cat, that will create pressure. The mode of operation of the system is to flow air to the cat between the two elements after the cat is heated up, so plugging it will create pressure in the system and you are liable to break something else.
Good Luck
There are two diverter valves which control airflow in the system. These valves (front of engine with two electrical and several vacuum line connections) route the air from the pump to one of three places;
Out the muffler on the front of the engine
Into the exhaust manifolds
Into the catalytic converter
You may be able to apply voltage to force the system to do what you want, but again, you should check the FSM before you start applying current.
The Air Injection Pump is a continuous flow vane pump, it will pump air at all times while it is in motion. YOU SHOULD NOT plug the line to the cat, that will create pressure. The mode of operation of the system is to flow air to the cat between the two elements after the cat is heated up, so plugging it will create pressure in the system and you are liable to break something else.
Good Luck
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
What Shark said!
This thread is ODD and that should be pointed out. The original premise is to restore OEM operation -- which isn't wasn't suggested RIGHT AFTER THE DECLARATION! Do you want to bastardize the system or not!!?!?!?
Shark is correct about the 3 modes (directions) of air flow. I have a divertor in my basement that I could pull out and study -- to figure this out for the OP...or he could do that himself. I'm not ready to because of the conflict in goal/purpose. I also have a perfect air tube (that I'll never use) that I could sell/ship to restore operation. I'm guessing neither will happen.
In considering the options for permanent routing, the OP has to consider if long-term, continuous flow of air into the manifolds or converter? (that's not there) causes any issue? I doubt air can be continuously pumped in the manifolds. Why? Because it would mess with the O2 sensor and make is run rich. (I apologize for not remembering why air is pumped into the manifold in the first place -- but I'm thinking it's only done at startup...when in open loop)
That means you have to choose between the air (CAT) outlet and the "muffler" -- which you don't like the noise. Plus, I have to say I'm uncertain if the "muffler" (bypass?) direction is causing the noise OR if it's the direction where you are missing the air tube (to the CAT). If it's the muffler, the original question isn't valid -- because the noise can't be "cured" without removing the system. If it's air escaping an "uncapped" air tube fitting (from the diverter), it seems like you just want to "vent" that air.
That implies disconnecting the air pump from the diverter OR removing the guts of the air pump -- which one/two people have done (erroneously thinking it would free up HP).
While thinking (out loud) and typing, I think the only solution is going to be removing the air pump components (and installing a delete pulley) or get an air tube and vent air back into the exhaust. FWIW, the tube COULD be routed (punctured) into a pipe anywhere -- especially if it's on the passenger side of a dual setup. There's no O2 sensor over there.
I apologize ahead of time -- if I'm not thinking of something. I built an engine 8 yrs ago and removed the AIR then. More over, my car hasn't run WITH the AIR installed for 10 years.
The biggest reason I'm replying to this thread is to encourage the OP to restore it -- as declared -- OR remove it. That's basically my 2 cents with as much thinking (background) I can regurgitate to support my thinking.
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So let me try to make my situation clearer. Previous owner "bastardized" the exhaust by cutting the cat out of the y-pipe and running dual pipes straight back. I would love to restore the exhaust, and I might at some point, but what's there is sound and new. Keeping the AIR system intact is my goal so that I (or a future owner) can relatively easily install a stock exhaust system. This is a project but I have to stick to a budget so it might be a few years before I get to the exhaust.
in its current state, the metal tube that feeds the cat is unterminated, wide open at the point where it would have connected to the cat. The sound is made when the air is pumped to that port, sounds like a trumpet. What I would like to do is spoof the system, not physically alter it or destroy it ("bastardizing") to not pump air through that specific route. The front muffler would be ideal, because as stated in the last post, continuos air into the manifold could screw with the O2 sensor unless I can divert it only to the passenger side.
while my goal is to restore to original,the exhaust system is low on my list for now, so a temporary workaround that doesn't damage the AIR system would be ideal.
I suppose another option is to have an exhaust shop route the air tube into one of the exhaust pipes beyond the O2 sensor.
I will review the FSM, it sounds like a there is potential to spoof the diverter valves without damaging anything. I just thought somebody else has run into this.
in its current state, the metal tube that feeds the cat is unterminated, wide open at the point where it would have connected to the cat. The sound is made when the air is pumped to that port, sounds like a trumpet. What I would like to do is spoof the system, not physically alter it or destroy it ("bastardizing") to not pump air through that specific route. The front muffler would be ideal, because as stated in the last post, continuos air into the manifold could screw with the O2 sensor unless I can divert it only to the passenger side.
while my goal is to restore to original,the exhaust system is low on my list for now, so a temporary workaround that doesn't damage the AIR system would be ideal.
I suppose another option is to have an exhaust shop route the air tube into one of the exhaust pipes beyond the O2 sensor.
I will review the FSM, it sounds like a there is potential to spoof the diverter valves without damaging anything. I just thought somebody else has run into this.
