Can someone explain this system for me or point me to previous posts that cover this:

Like to understand the function, components and routing for the smog/air pump on late models (covering GTS).

Seems the ouput of the pump goes to a diverter valve (where?, vacuum actuator & solenoid controlled?, by the ECU? delay timer?) and is fed to the cats only when they are not yet fully hot? then after this point it seems the diverter valve dumps the flow into the intake flow (is this the port opposite the breather connection on the throttle body?, what else connects there (I see an asymetric "T" I think - if thats it...?) Doesn't that flow mess up the air metering since it does not flow through the MAF? is it compensated for somehow? where does the air get introduced to the Cats? If the airpump is deleted does any compensation need to get taken back out?

Thanks for whatever pointers you have on this?

Alan

 

Alan,
You have the basics. It dumps the air into the air box before the MAF.
See PET illustration108-00 in 93MY.
Roger

 

Ahh OK thats what that hose is - makes sense to ensure its metered - where is the actual diverter valve located?

And - seperate question now - what is fed by that drivers side port opposite the breather on the TB (after MAF, before throttle plate) - seems the small port on the "T" goes to the vac booster venturi and the other somewhere under the intake... what's that for - ISV? / more ?

Alan

 

From the air pump runsa rubber hose which attaches to the diverter valve. The pump diverter valve attaches to a bracket that is bolted to side of the right head, appr. 1/4 or 1/3 down to the rear. From the diverter valve directly down runs a metal pipe which boltedmto the stock exhaust pipe a bot behind the mating flange to the exhaust manifold. From the diverter valve back runs a short rubber hose which connects to the underside of the air box cover, a few inches down from where the intake hose sits.

 

Aryan - thanks!

 

From the T on the drivers side the rear most port goes to the venturi, the forward port to the ISV.

 

The diverter dumps pressurized air into the airbox at full throttle (low vacuum).

This is partly to lower exhaust temperatures (less afterburning of HC), but I think it is also done to protect the air pump so that it isn't damaged by trying to pump too hard, at too high of an rpm.

The outlets in the cats (or heads) are quite small/the pump is developing quite a bit of air pressure.

 

The diverter valve is fed vacuum from a port on the underside throttle body. The port is closed when the throttle plate is closed (engine idle/off). The diverter is an open closed switch so the pressurized air from the pump is fed to the air box or the cats accordingly.

If you require any air pump associated parts Im removing the system from my GTS.

 

Malcolm - thanks - but no need, I'm also considering removing it.

I do plan to add an X pipe and new high flow cats, will take out then if not before. Would probably have done this already but too many other things came up over last few months (work stuff, house stuff, holiday stuff and other issues - like my drivers door handle busting - parts on order... )

Considering adding a vac pump in place of the airpump (as Colin has done) to evac the crankcase, would need a path for this:

2 main plumbing options:

1. Vent fresh unmetered air into the heads from the airbox bottom and dump post separated air back from the crank back into the airbox (use the airpump feed port)

OR

2. Vent fresh metered air into the heads from the TB ports and dump post separated air back from the crank back into the TB, the problem is that the current TB ports are really too small (combined) and may still need a blow-off - OR I may just double up and adapt to use the port on the other side of the TB, the flow is never really in competition since this one would flow into the TB only.

Still thinking it through...

Alan

 

Just to complete the thread here is a visual from the '87 spec book:

 

Malcolm - thanks - thats a great picture of it.

Alan

 

That picture is of a non-cat S4 motor. Items 2 (diverter valve) and 3 (one-way valve - prevents exhaust coming back up) are the same.

In the pic you can also see the manifold which is plumbed into each exhaust port, where the air is injected via banjo bolt fittings.

 

I have been considering air pump removal on my 85 928S US, as well as x-pipe, and high flow cats.
I know the high flow cats don't need the air injected into them, like the stock system.
Is there any negative to eliminating the air pump and not having air pumped directly into the air box?
Are cold starts more difficult?

 

Air is pumped to the cats or heads most of the time. It only goes to the airbox at full throttle.

I reckon bypassed airpump air is dumped to the airbox to muffle the sound.

 

I'm not sure how high, but the airpump is designed to pressurize the air.
The injection holes are quite small.

Even if you can separate liquid oil, I don't think the stock pump can handle the amount of water vapor that comes out of the crankcase.


I was thinking about this the other day, again, and I found this on eBay.

The airflow conveyor below wants 16 SCFM @ 80 PSIG.
I think the airpump could manage some of that, at least.
It might draw a bit of vacuum in the crankcase, or at least pull fresh air through it.

http://www.streamtek.ca/
http://www.ebay.com/itm/290348981188