Will a catalytic converter work on an old car? - PeachParts Mercedes-Benz Forum

t walgamuth · #1 01-29-2012, 06:34 PM

I have an older vehicle which does not have a cat. It's exhaust stinks. Could i put a cat into the system without any other electronic devices and clean up its exhaust?

sixto · #2 01-29-2012, 06:47 PM

It's only recently that cars have an O2 sensor downstream of the cat and I think it's only to check the health of the cat. That means about 35 years of no electronics downstream of the cat.

It might make more sense to hook up an O2 sensor and gauge and tune it to stoich.

I have a Gunson Colortune in my toolbox if you'd care to try it

Sixto
87 300D

t walgamuth · #3 01-29-2012, 06:58 PM

So will it work or not?

JiveTurkey · #4 01-29-2012, 07:34 PM

I think if the catalytic converter is matched in terms of similar exhaust gas content and flow it should work right? But make sure it's enough to get the job done. You wouldn't put a band air on a severed femoral artery; too much flow for the fix to make much of a difference. See what I mean?

loepke72 · #5 01-29-2012, 07:36 PM

If you're looking to install an older style oxidation catalyst, then yes, it can be done but you will need to add some way of injecting air into the exhaust system before the converter. Also you will need to keep the car in good tune so you don't end up with excess fuel in the exhaust and end up overheating the converter. You'll need to inject air because normally a carbureted car runs on the rich side of the ideal air-fuel ratio. That is because slight variations in air/fuel ratio on the rich side of ideal have a much smaller effect on engine performance versus the same variation on the lean side. When an engine is running rich, there is an excess of fuel and very little oxygen in the exhaust. Without enough oxygen, the converter can't do its job (oxidize), so it'll be necessary to inject air, or else you might as well leave the converter off as it won't do much at all. That's why the older cars had an air pump. Three-way catalysts will require the use of a closed-loop fuel system (O2 sensor).

Newer cars with three-way catalysts get away without the air pump because of two reasons: One is the air/fuel ratio goes either side of ideal, which allows some oxygen into the exhaust, also the reduction converter strips the oxygen out of the NOx emissions before the oxidation converter.

No matter how well you tune an engine, there will be unburnt fuel if for no other reason than the combustion process generates CO2 which acts as a fire extinguisher in the cylinder. So there will be exhaust odor no matter what on a non-catalyst car.

rscurtis · #6 01-29-2012, 08:41 PM

What kind of car are we talking about? Any old car (or engine) that I've ever owned has a nice clean smell in the exhaust if it's running properly. If it stinks or burns your eyes, there's something wrong with it.

Edward Wyatt · #7 01-29-2012, 08:58 PM

Quote:

Originally Posted by t walgamuth

So will it work or not?

No, it will not work, any other questions?

t walgamuth · #8 01-29-2012, 08:58 PM

Its an 87 mitsubishi montero, my plow truck. I suppose it originally had a converter but did not when I got it. It smells stinky so maybe it is running too rich.

It sounds like to make it all work well I would need an air pump and an o2 sensor.

unkl300d · #9 01-29-2012, 09:01 PM

Maybe a rodent nested inside the exhaust and is now cooked???

t walgamuth · #10 01-29-2012, 09:05 PM

Quote:

Originally Posted by unkl300d

Maybe a rodent nested inside the exhaust and is now cooked???

I don't think so.

Edward Wyatt · #11 01-29-2012, 09:21 PM

Quote:

Originally Posted by t walgamuth

Its an 87 mitsubishi montero, my plow truck. I suppose it originally had a converter but did not when I got it. It smells stinky so maybe it is running too rich.

It sounds like to make it all work well I would need an air pump and an o2 sensor.

It already has a O2 sensor.

Adding an air pump isn't realistic, and they work only on cold starts to help get the cat warmed up.

sixto · #12 01-29-2012, 09:37 PM

An 87 Montero has EFI so a later style cat should work since it had a cat when new. Since it has an oxygen sensor, build something like this for a peak into the fuel management workings - DIY Air / Fuel Ratio Meter

Sixto
87 300D

t walgamuth · #13 01-29-2012, 09:55 PM

Actually somewhere under a huge spagetti bowl of vac hoses there is actually a carburator. I have not actually searched for an o2 sensor so there could be one there somewhere, but didn't someone say it would be behind the car?

Sorry I am a diesel guy so am not all that sure about gasser technology when it comes to emissions.

sixto · #14 01-29-2012, 10:14 PM

I checked a few parts stores and they all show an oxygen sensor so there's a good bet it has one, or used to. It would go between the exhaust manifold and cat.

Sixto
87 300D

t walgamuth · #15 01-29-2012, 10:21 PM

Thanks Sixto!

If it has an o2 sensor do you think there is a chance that just installing the cat might do the trick?

I checked your link above and it looked a bit intimidating.

I have a presumed good cat from my Miata so I just thought it might work to just put it in the system and go. If it gets much more complicated than that I probably am going to pass. The truck does not get driven all that much.