How do I reduce Hydrocarbons at idle?
 

I took my car through emissions to day and passed everything but the idle test. I have a 79 GS. I took it through three months ago and it failed with a reading of 891ppm. I drove it for about three months (It had been sitting since 1996) and did an oil change and new plugs before going this time. As well I leaned the car out at idle. This time it was even higher 1481ppm. I need to get it down to 435. I actual have to pass this time to reinsure my car. Anyone have any ideas? Is there any way to cheat my way through this?

AdamP
1993 RX-7 Touring
1979 RX-7 GS

Don't they have a thermal reactive exhaust? Do you need to richen fuel in order for the reactor to work properly? Anyone?

OK, from memory here but lets see how well I recall this stuff....

If I remember the overall theory right, at higher rpms, the air is sent into the thermal reactor to help cool and at lower speeds it is supposed to be sent to the catalytic converter for additional oxygen for the reactions to convert CO to CO2. Obviously make sure the hoses running to and fro are good - particularly the one that runs back to the cat.

The air pump pumps air and its end destination is decided by the checkvalve (controled by vacuum), either it goes into the thermal reactor or to the main cat. So first check your air pump and make sure it is pumping air by pulling its back hose. Then you can check the check valve at the other end of that hose to make sure it is working right. I would suspect all this is working cause it is pretty rudimentary stuff and there is not much to go wrong.

The secondary air control system would be my likely guess cause this controls everything. There is a solenoid and an air control valve - the solenoid is the one with the blue sticker (I only know this cause I swapped it from my set of spares and that's the one missing) or the second one behind the alternator. You will need a multimeter to check it. Somethings triggers it to switch by voltage change, can't rememeber what. But if that is working and everything else is working........

If you check everything out and still don't pass, you may want to just run the hose that normally goes from the checkvalve to the thermal reactor to the catalytic converter pipe instead. Just remember to switch it back after the test or you could overheat your thermal reactor.

Someone who has touched this within the last three years, check this and make sure I remember it correctly ;-)

I just realized you have a 79, that does not have the pipe running back to the cat so that removes a possibility. So your choices of destinations for the air are either the thermal converter or the heat exchange at whick point it gets routed into the engine, I believe the exhaust ports.. Not sure it has the pipe running back to the cat - you could tell that better than I.....

WEll if you are just aiming at getting though emissions test, simply raise your idle to say 1300-1600rpm and turn the idle mixture down a little. Go to the test and then set it back to what you had it when you leave.

When you use stock idle, you get more emissions due to factors such as overlap and the seals seal better above idle better and emissions clean up. By leaning the idle mix screw it will remove the HC's but may introduce a little more CO which isn't as much of a concern in CA emission testing I'm told. Sure you are getting more exhuast out the rear, but the quality is better in off idle conditions.

well my dealings with 7's and smog is 90% of the prob's are the acv.... air control valve.

If it was sitting for 5 years, you need to rebuild the carb before you can get any of the emisssions systems to work as designed. The thermal reactor takes the exhaust which has unspent fuel in it and burns it again with a stream of air diverted from the air pump. The rest of the air is sent into the shell around the thermal reactor to prevent it from becoming a rolling foundry on your engine. The point of all this heat is to burn up Nox and HCs left after the combustion process. Cats do it chemically with rare metals, but you won't have one in RX7s until 1981. Start with the carb....:cool:

If there is no under hood inspection, you can always up grade to the later exhaust and plumb the air pump strait to the cat. avoiding the ACV altogether. This has worked for me down here in Wa. BUT, if there is an under hood inspection you are better off going the hard route, esspecialy if the inspection techs know what they're looking for.
Ryan

I did rebuild the card when I first started driving it. There is no underhood inspection. It is for Vancouver Aircare emissions in BC Canada. I am going to work on it this weekend. I think I will try raising the idle. I want to go back to inspection as few times as possible because it casts $25 each time I go. Thanks for all your help so far guys.

Make sure you're timing is at factory specs or even a little retarded. Don't rev past 5000 RPM while it's on these settings and drive for a half hour or so prior to going to the inspection center. Once there, don't stop the engine while waiting for your turn. You'll have leaned out the idle mixture before all of this. After inspection, change the timing and idle mixture back to safe specs. Changing the oil adn air cleaner will also help get it down into the 180s-220s ven with a leaky thermal reactor. :cool:

Thanks for the help guys. I trund the idle up to 1100 and retarded the timeing a bit and I passed with flying colours.

AdamP