ok ive got a 92 f150 with the efi 4.9l and all the neat smog stuff...well there is a metal tube running from somewhere on the smog system down to the exaust just ahead of my cat if i remember correctly...well this tube rotted about 1/2 an inch outside the exaust pipe...my question is is it ok to leave this alone...should i plug it off and also should i plug the open in the exaust somehow also...just wondering

 

What I did was weld the hole in the main exhaust pipe shut and rip off that tube. But the truck I did this on was not worth fixing the right way. It won't hurt anything, it just helps the cats light off faster after a cold start.

 

so it is to my understanding...that should i just leave it hanging and leave the opening in the main exaust it wont hurt anything.....but would it be of any benefit to the gas mileage if i were to block off that opening

 

On my 87 F250 5.0 I also had same problem which I let go for a while. tube led to egt sensor so truck didn't lean out properly when warmed up. not a big difference but I noticed a drop in fuel econemy

 

Plug the hole in the pipe but DO NOT plug the line, the pump will get noisy if you do.

 

I didn't think it would hurt mileage, it's just sending fresh air into the exhaust to make the cats work better when the motor is cold. I personally decided to block off the hole in the main exhaust because I didn't want exhaust constantly coming out right under the cab. Good way to get dead from CO poisoning...

 

It helps the catalytic converters light off at ALL times, not just startup.

A catalytic converter is simply that, a housing in which several substances are converted to another through a catalytic process. The honeycomb of stuff in there is simply surface area for the catalytic process to occur. This is between hot exhaust gas (as hot as possible, hence catalytic converter placement at end of manifold) combined with a fresh source of O2. Many of the dangerous substances are turned into a variety of oxides. CO becomes CO2, just as the nitrogenous gases are converted. Also helps to break down more hydrocarbons before they pass the tailpipe.

If you have emissions, you need to either reconnect the pipe, or get a new catalytic converter that can exist without a fresh supply of air being injected.

Having the pipe disconnected should not cause you to richen up, lean out, etc. It is past the O2 sensor (this could be dif on 96 models, or other OBD2 models), so it pays no harm. The only problem here should be the sound that this leak puts off. My 300-6 has the same problem...air pipe broke open due to run in with snow this last winter. My mileage with that truck is 18mpg, probably even 19 on the highway but 18mpg overall on a tank. That's very respectable for a 300, the air pipe being opened up isnt' hurting anything except sounding like crap.

Gatesj, funny you should mention that. With my aforementioned exhaust leak, I took my truck for a drive down the road and back with my center floorpan pulled so I could watch the transmission and look for gear oil leaking from the tranny. Oh....I had to get out when I got to the stopsign (2 miles down the road) so I could get my head straight. Then I got back in and drove really fast all the way home with the windows down and everything - ugh! Not a smart idea.

 

Saurian: This is really interesting. I have a question but first I have to explain my understanding of how this works.

This is the way I understand that most catalytic converters work. Given a near perfect fuel mixture at normal engine temperature, there are near equal amounts of unburned hydrocarbons and oxides of nitrogen in the exhaust. The catalyst simply catalyzes a chemical reaction that produces CO2 and H20 from the hydrocarbons and oxides of nitrogen. With a near perfect mixture there is enough of both types of chemicals to break down and combine; this is why mixture is sooo important for emissions.

I understand the A.I.R. reaction is slightly different, during warmup the engine runs a little rich so there are way more unburned hydrocarbons than oxides of nitrogen and these are simply burned while flowing through the catalyst by injecting fresh air to provide oxygen for the combustion.

They're two completely different types of reactions.

My '95 with the 351w, which I would assume is similar, injects air into the exhaust stream between converters, but only during the first few minutes after a cold start, and it slowly tapers it off during those few minutes. I know this because I have been messing with a leak on that truck too.

I have an import with Bosch Motronic engine management, which I know intimately. I can tell you on that the computer runs an electric air pump that injects fresh air right into the head behind the exhaust valves, but only for exactly two minutes after a cold start. This obviously helps burn off the gasoline in the very rich exhaust and helps the converter light off. Once it's lit off it's lit off. At two minutes, the O2 sensors come online and because the computer can now meter fuel precisely it doesn't need the air pump; the catalyst can work like it's supposed to with a good mixture.

With that having been said, my question is, is this how the Ford converters work, or do they depend on a different set of reactions? I remember hearing that one converter catalyzes part of the process and the second finishes it.

Is the first converter what takes care of the normal running, combining hydrocarbons and NO to make H20 and CO2, and the second is simply a ceramic matrix to assist with the A.I.R. reaction?

I guess I thought the only place that an air pump helps you is if you're running rich, like on a cold start.