Flowmaster Y pipe with Cat question
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4wd Low
Joined: Feb 2023
Posts: 11
Likes: 3
From: Kentucky
Flowmaster Y pipe with Cat question
1993 302, AT. All stock, all smog still in place
Replacing stock Y pipe and cat with a flowmaster Y and Cat. Reading previous threads, I know the tube coming off of the cat is really not needed to be hooked up, but if I don't, can I leave the injection pipe going to the cat open? Or do I need to cap it off somehow?
Replacing stock Y pipe and cat with a flowmaster Y and Cat. Reading previous threads, I know the tube coming off of the cat is really not needed to be hooked up, but if I don't, can I leave the injection pipe going to the cat open? Or do I need to cap it off somehow?
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4wd Low
Joined: Feb 2023
Posts: 11
Likes: 3
From: Kentucky
Well I don't have access to a welder or tubing to be able to extend to the new cat.
From what I read, all the injection tube does is inject air into the cat at start up to heat it up quicker. Once it heats up, the tubing isn't doing anything else
From what I read, all the injection tube does is inject air into the cat at start up to heat it up quicker. Once it heats up, the tubing isn't doing anything else
FTE Legend
Joined: Nov 2015
Posts: 30,955
Likes: 4,127
From: Angier, NC
How do you think air blowing across a cat that is to get hot to work is helping it heat up?
I never heard that what I have heard is there is un-burnt gas but no O2 for it to re-burn again from the heat of the cat so the air injects the O2 so it will re-burn and get a lower tail pipe reading.
Me really thinks you are putting air into a system that is rich and deluting the exh gases for a lower reading but what do I know.
Would you not get a lower reading pumping air into the system with out a cat?
I am guessing the new FM cat dose not have a hook up for the air tube as newer cars and trucks dont.
I think I would just cap the tube end so nothing would go up the tube and pull the belt on the pump so it is not dead headed pumping to that caped tube.
If the cat dose have a hook up for the air tube they make a repair for them IIRC. Think Dorman makes it?
Could get copper tubing, easy to bend if needed, and small exh clamps to make it longer to fit.
Dave ----
I never heard that what I have heard is there is un-burnt gas but no O2 for it to re-burn again from the heat of the cat so the air injects the O2 so it will re-burn and get a lower tail pipe reading.
Me really thinks you are putting air into a system that is rich and deluting the exh gases for a lower reading but what do I know.
Would you not get a lower reading pumping air into the system with out a cat?
I am guessing the new FM cat dose not have a hook up for the air tube as newer cars and trucks dont.
I think I would just cap the tube end so nothing would go up the tube and pull the belt on the pump so it is not dead headed pumping to that caped tube.
If the cat dose have a hook up for the air tube they make a repair for them IIRC. Think Dorman makes it?
Could get copper tubing, easy to bend if needed, and small exh clamps to make it longer to fit.
Dave ----
Hotshot
Joined: Jul 2020
Posts: 10,551
Likes: 2,669
From: Near Salt Lake City
That mid bed air supply to the cat does need to be hooked up
Otherwise, the cat will not have sufficient air to burn away the HCs and could plug up quick
If Flowmaster designed it that way on purpose, not so much trouble then
If the new cat has the tube, hook it up
Otherwise, the cat will not have sufficient air to burn away the HCs and could plug up quick
If Flowmaster designed it that way on purpose, not so much trouble then
If the new cat has the tube, hook it up
Cargo Master
Joined: Aug 2021
Posts: 2,261
Likes: 744
From: Maryland
I connected mine with parts from Walker and I got the high temperature hose on line.
I'm not sure all new catalytic converters require air. I would ask the manufacturer that question.
The default setting for my air system, on cold starts, is to bypass the air pump air, so its not going into the exhaust or the converter.
After about 90 seconds, the valves send the air into the back of the heads. After the engine warms up, the air is sent to the catalytic converter. The ECM determines where to send the air on hot restarts after that.
If you connect your air tubing to your converter, verify that the check valves in the system are working. I had to replace my check valves. Otherwise, the hot exhaust will damage the diverter/bypass valves.
Looking up at the air injection tube and check valve that run from the back of my engine to the catalytic converter.
The green high temperature hose that runs from the catalytic converter to the tubing in the previous picture. I added the clamps to keep it from rattling, etc.
If you find out that your catalytic converter doesn't require air injection, as long as your diverter valves and check valves are working, you could just leave the tubing to the converter unhooked. The only problem with that would be if a check valve fails, that tube could leak exhaust from the back of the heads.
Lead Driver
Joined: Jan 2019
Posts: 5,083
Likes: 868
From: N.W. Alabama
Don't forget, that he didnt state, if F150 or F250/350, F150 had the pipe/tube in 2nd converter, not first, and it could still be hooked up, where as a F250/350 only had 1 converter.
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Cargo Master
Joined: Aug 2021
Posts: 2,261
Likes: 744
From: Maryland
When I bought my truck, the entire stock exhaust had been replaced. I installed a Walker Y pipe and one cat after it, with an air injection tube. According to Walker's fine print, the cat I installed is an acceptable replacement for what was a two cat system.
In Maryland, for normal registration, the exhaust emissions system has to be present and "complete."
There is a historic registration that doesn't require strict inspection but driving is limited by mileage, whether you can have passengers, etc.
Since I was starting from scratch, I put it back to as close to stock as possible.
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