Air Pipes to Catalytic Converter Question-Photo added

This question was moved here for me in case there is a truck engine mechanic ( or at least somebody who knows) who would know the answer. (No luck on Class C)

Boils down to the question-- which of the two pipes on the catalytic converter on a 1991 E350 460 EFI goes to the secondary air pump pipe that comes down from that on the passenger side at the back of the engine?

The top one in the middle of the Cat or the pipe at the front of the Cat?

Thanks

jimx200 wrote:
Remove all that CAT stuff and install a set of headers.

They have relaxed the rules here on that, so you do not have to replace a bad cat here, but there can be an issue with the oxygen sensor left out so your fuel air mix will be too rich, but there is a fix for that. Lots of info on Google for how to do all that.

Still looking for confirmation that the pipe from the air pump goes to the pipe from the middle of the cat on top and not to the pipe at the front of the cat.

Remove all that CAT stuff and install a set of headers.

In this area this vehicle would be exempt from emissions testing because of year and size.

Some people have removed their air pump systems all together. Some remove their cats. Others gut their cats and weld the pipes closed.

If you have need to make a "Test pipe" to "temporarily replace" your catalytic converter for "test purposes" this adapter fit the cat flange we had perfectly and even included the gasket.

Flange adapter

The air pump/computer did not suffer an ill effects and doesn't have any engine error codes or light.

Seeing as the pipes for the air pump aren't even available any more and they tend to rust out, I would be looking at different options.

IMHO, having exhaust tubing run up into the engine bay and then transitioning to rubber hoses is not the brightest design anyways, even with check valves and such.

But that is just my opinion. Each person has to make that choice on their own.

Got this from Wiki: I think it says there can be two inputs. They are not for cooling the cat--that was wrong info previously posted by me above.

"When catalytic converters were first introduced, most vehicles used carburetors that provided a relatively rich air-fuel ratio. Oxygen (O2) levels in the exhaust stream were therefore generally insufficient for the catalytic reaction to occur efficiently. Most designs of the time therefore included secondary air injection, which injected air into the exhaust stream. This increased the available oxygen, allowing the catalyst to function as intended.

Some three-way catalytic converter systems have air injection systems with the air injected between the first (NOx reduction) and second (HC and CO oxidation) stages of the converter. As in two-way converters, this injected air provides oxygen for the oxidation reactions.

***An upstream air injection point, ahead of the catalytic converter, is also sometimes present to provide additional oxygen only during the engine warm up period.**** (Is that the second air pipe to the front of the cat?)

This causes unburned fuel to ignite in the exhaust tract, thereby preventing it reaching the catalytic converter at all. This technique reduces the engine runtime needed for the catalytic converter to reach its "light-off" or operating temperature."

Ok but my E350 has EFI. So why does it even have a secondary air pump? Anyway, it seems very difficult to find out what the two pipes are that go into the cat. :(

EDIT--so far I am guessing from that Wiki entry that the pipe from the air pump goes to the middle of the cat (for the between reduction stages business) and the other pipe goes to the front ("ahead of the cat") for the warm up time. Can anybody confirm? Thanks.

More Wiki:
"and particularly when the catalytic converter was introduced, the function of secondary air injection shifted. Rather than being a primary emission control device, the secondary air injection system was adapted to support the efficient function of the catalytic converter. The original air injection point became known as the upstream injection point. When the catalytic converter is cold, air injected at the upstream point burns with the deliberately rich exhaust so as to bring the catalyst up to operating temperature quickly."

BFL13 wrote:
If the air is to cool the catalytic converter, would one pipe be for IN and the other for OUT? If the red circle thing is the pump that would be IN I guess. Would it go on the pipe at the front of the cat conv as an intake, and the one on top in the middle is for OUT? Is that to the engine for recirc or is that only with the other smog system?

The other pipe goes along the top of the right side of the engine, has a short rubber hose connection to another pipe going farther forward passenger side, then I don't know where it goes.(recirc?)

I don't have a clue, but have to think it matters which goes with which.

This is where I am unclear. From what I've seen and read, it provides additional air for combustion efficiency in the catalytic converter (remember way back they were touted as "secondary burn"?), hence the check valves.

I don't know what that extra missing piece is, though. I read about diverters and things but they were on different engines. I haven't found a good, clear description or diagram of the system and its parts.

Even when I found parts listings, no pics :(

Maybe someone knows if both pipes push air?

deleted IN and OUT notion

Here is a thread explaining some things about the air pump Thermactor system: https://www.ford-trucks.com/forums/1076650-air-injection-and-smog-pump-delete.html

Sorry I don't have the answer you are looking for. But I am still searching.

From my pics, it seems that if the lines don't cross, the one at the middle of the catalytic converter (not the front) is closest to the engine.

Does it matter which line is which? I don't know or why?

A garage guy says there would definitely be two rubber hoses there to connect the two sets of pipes. I just want to know which pipe connects to which pipe for now. Looks like a Murphy waiting to happen.

This video (not mine) might show a bit: https://youtu.be/hIiUXbrEkPc