Hi guys, I see AIR divert will affect how the bin treats O2 values. When AIR diverts where does it go? Under what engine run conditions will it divert? I have a TPI 305 that I would like to run a carb on for a short time period. I have the AIR system intact and would like to keep it functional enough to pass emissions. Is there a switch for AIR divert that I will have to make sure is not diverting when I have no ecm connected?

 

It's my understanding that AIR doesn't have to be functional for an emissions pass.

The air helps to light the cat faster during initial start-up and then diverts. When the car is hot, undergoing testing, it's in divert mode and not a part of the equation, as I understand it. Feel free to correct me, anybody, if warranted!

 

I know computer controlled carbureted vehicles came with AIR from the factory. How were these set up? Did they run AIR all of the time, or did the computer still divert during normal operation? What about non computer controlled carbed vehicles with AIR? I know these existed in the late 70s-mid 80s on carbed, non computer controlled trucks. Did AIR run all of the time on those?

 

the AIR is injected into the manifolds when the motor is cold, as the motor warms up it is diverted to the cat, the AIR must be diverted to the atmosphere when ever the car is in Deceleration, if it is not diverted, it will cause a backfire in the exhaust & may well blow out the muffler.
the older cars used thermo & vacuum control valves to divert the air, its part of the reason why they had so many vacuum hoses on them.
on most motors, the cat needs fresh air to do its job properly.

which car are you wanting to run a carb on?

i don't know if you can do this or not, but if you can, use the TPI computer to control the AIR system, i don't know if it needs the TPS or not, it seems like it uses the MAP sensor the divert the
air to the atmosphere in decel & the coolant sensor to divert between the manifolds & cat.

 

Denn, it is a 1983 Firebird with a 1987 TPI 305 going in. I will convert back to TPI eventually, but I want to run the car carbed for a while to shake down the used motor. I have a big, extremely inexpensive U pull it truck yard around here. I suppose I could get the computer from a CCC Q jet and also use the CCC Q jet carb. That would work, right?

 

that would work just fine

there isn't much to the wiring harness on those old 3-C systems.
i would look for something out of a 84-88 chevy, like a monte carlo as they made a bunch of them it will probably be easy to find one in pretty good condition. the oldsmobile systems were kind of strange in what they wanted to go into closed loop, so i would stay away from them.

the O2 sensor & coolant temp sensor you have will work fine with the 3-C, though you may need to change the connectors on the harness.
you will need the 3-C MAP sensor & maybe a speed buffer for it.

 

I've found that at least the CCC system on an 85 Celebrity injects AIR during conditions other than cold start. It's weird. Some cars have hoses right to the cat. Others, like my Caprice, had a one bank multiport AIR setup (on the opposite side as the cat).

 

I suggest searching for RBob's and/or Grumpy's comments on this. I seem to remember that are lots of different times (at least on the 730 TPI $8D configurations when the divert is to manifolds vs. cats, and when it is diverting to atmosphere. It's not as simple as it sounds, not cut and dried, if I remember correctly.

However, for what you're wanting to do I don't know if that will matter much or not, sorry.

 

It definitely varies, a lot. I know that some calibrations use different O2 voltage thresholds when AIR is injecting. My Caprice, for instance, injected on the bank opposite the O2, so it would have never bothered the O2 anyway, even though I don't think it injected after cold start, or during closed loop. The LT1 cars, also, have electric AIR pumps. And their operation IS pretty cut and dry. They run a few minutes on a cold start (defined by the CTS value at startup) and then shutdown for the remainder of the ignition cycle. Interestingly, at least for the LT1 Caprices, GM released a TSB that said the AIR is not needed to retain emissions compliance (obviously not for the sniffer, but compliance with all of the EPA's rules). So owners commonly disable the system, as it tends to fail (water gets in there). I think newer cat technology allows the AIR system to be less functional.