CATALYTIC CONVERTOR NEEDED

[solarlord]

Hi- 87 terc 4wd catalytic convertor leaking need a replacement part any ideas its abt 16inches long- have bought parts from Autorock and have had no trouble with postage to the UK- but there is large number on offer and dont know where to start -thanks in advance -DEREK

[Petros]

there should be after market replace catalytic convertors available for not too much money. I do not know how good they are, but this car does not have the cat operation as part of the fuel management system, so it will not affect the way it runs.

Are you required to keep the cat on the car where you live, no matter how old the car is? when mine fell apart I just had a muffler shop install a by-pass (straight) pipe, where I live cars over 25 years old are exempt from emissions requirements. But I know that is not true in other states.

[solarlord]

Petros- yes i agree about making a by-pass that is what i would do and in spain old cars 20 plus years dont need a cat- but there is a emission hose comming from the rocker box down to the cat and going into the cat via an steel tube attached to the side of the cat- taking this hose out might cause problems or not i dont know- the problem its a Swiss car and they were the first country to introduce cats way before anybody else-funny thing in spain its the only terc and nobody as ever seen one in the flesh,but when drive about all the young guys wave and shout ,i think they have all seen breaking bad, anyway what to do about this emission pipe,might have bite the bullet and fit one from Autorock-whats your view -tar and thanks DEREK

[xirdneh]

that steel tube terminates near the starter
i believe it just takes in a bit of air for the cat
so if you remove the cat remove the tube too

[solarlord]

Petros- right you are ,will do ,if i remove the cat and put a straight thru pipe will there be a loss off back pressure ,if so shall i advance or retard the timming-thanks DEREK

[irowiki]

The back pressure thing is a myth and you don't need to worry about it.

[lannvouivre]

that steel tube terminates near the starter
i believe it just takes in a bit of air for the cat
so if you remove the cat remove the tube too

It's air injection that uses ram-air instead of a pump. All it does is add weight Its function was to inject air into the cat for more complete burning of pollutants in the exhaust.

[dlb]

The back pressure thing is a myth and you don't need to worry about it.

i'm going to go off-topic and say that i had a 15-passenger dodge van that had the exhaust come apart where the head pipe came down from the engine and met the straight pipe. i was driving at the time and far more noticeable than the change in exhaust sound was the sudden lack of power. i thought i fixed it at home but it happened again a few weeks later and same thing, the lack of power was much more noticeable than the sound. so i think there must be something to the idea of back pressure but i have never bothered to look it up. maybe it applies more to larger engines with more torque? not sure.

[Petros]

Derek,

Just remove the extra air intake tube for the cat, as stated it allows fresh air into the cat for more complete burning of combustion products. You will not need it and it will not affect how the car runs at all. Irowiki is correct, the back pressure thing is a myth, the lower the back pressure the better power and economy you will get.

It is understandings like DLB found that perpetrates that myth: the properly working exhaust system actually has pressures in it lower than the ambient pressures because of the dynamics of the exhaust pulsing down the system (in effect it creates a vacuum in the exhaust system). If you cut open the system the "back pressure" actually increases, and you get less power. the old straight pipes put on old drag racers and "rad rods" actually produce less power than a properly designed collector and tuned length exhaust pipe.

Think of it this way, if you put a powerful vacuum on the exhaust you could actually spin the engine without using any fuel at all, so you would have more power output with lower pressure in the exhaust, how would "back pressure" help you?. the full length exhaust system will produced pressures below the atmosphere when running properly, in essence "sucking" out the exhaust as soon as the exhaust valve opens. Removing the catalytic converter also means the engine has to work less hard to push the exhaust out past it. It likely has stopped functioning long ago anyway, so it will make nothing worse to remove it, and you will use less fuel with it removed to drive the same distance, so you will use less resources and put out less emissions per kilometer driven.

in fact, the air intake tube would not work at all if there was pressure higher than atmopheric pressure in the exhaust system. It has no pump, just a reed valve that is basically a one way valve. allows fresh air in when the pressure in the exhaust pipe is lower than the atmospheric pressure, but prevents burping of exhaust if the pressure builds up in the exhaust pipe during a back fire, low speed driving or if it is backed up. Without a pump it would not work at all it this was not true.

[Mark]

My wagon had the pipe going from the middle of the catalytic converter up to the engine bay next to the alternator. There's a check valve in it to prevent exhaust from travelling up it at idle or low speeds. At higher speeds, the draft of the exhaust flow through the cat causes air to be sucked in through that pipe. The additional oxygen makes the catalytic process work more completely. The pipe is made of aluminum and mine broke off next to the cat. I removed the aluminum piping and left the hole open for awhile, but it was noisy at idle or when I took my foot off the gas pedal. I ended up capping the hole with a copper pipe cap. The 2-stage cat now probably doesn't work as well, but a 30+ year-old cat probably didn't work that well anyway. If I were you, I'd replace yours with a generic aftermarket cat which is 1-stage and doesn't need that air intake pipe.

[eddie k]

The as reed valve/ check valve on my tercel has completely rotted away. Has capping the pipe worked well for you so far? I know finding a new one will be about impossible and I would hate to replace the cat, due to the fact I still haven't truly drivin the car yet to know what else I will be replacing

[Petros]

Welcome to the forum Eddie

it will not harm anything to cap it off. unless you are in a state that requires testing and inspection of cars this old. If you need one I am sure there are other forum member that have reed valves in boxes of parts they are not using (I may even have one somewhere you can have), likely for just the shipping cost.

where are you located?