böst

If I were to have a wideband sensor installed in my downpipe (on a stock turboII) would the air/fuel reading be misled by the stock airpump (that thing put there to pass emissions by pumping air into the exhaust air)?

Scott 89t2

I've thought about this too. it will make the readings show leaner when the air pump is pumping air into the rear port. however I'm not sure when it does this, as it turns on and shuts off. I think over 3800 it doesn't pump any air in, but I'm not sure.

No7Yet

(Argh. My spacebar don't like to work, so this will be short)

No. Airpump is further downstream, only affects readings past the main cat.

Brandon

HAILERS

BRANDON....Not so. The *Port air* funciton of the acv, ports air from the airpump to the acv, thru passages in the front and rear end housings to the rotor housing, and from there into the exaust ports of the front and rear rotor housings. It exits around the *diffusers* in the exaust ports. That means that the airpump air does exit prior to the 02 sensor, at idle anyway.When you step on the gas the switching valve *switches* and the air goes to the split air which does go to the cat aft of the 02 sensor. Your right about the 3800 opening the relief valve and dumping the airpump air overboard, so we shouldn't have a problem there. Then you've got the aav part of the acv dumping fresh air into the intake during deceleration, but really, who's interested in what happens when you lift your foot? If your interested in idle ratio you could just pull the vac line for the switching function off the acv.
EDIT: This thread and the answer by SixRotors is more coherent: https://www.rx7club.com/forum/showth...threadid=46139

No7Yet

Doh. HAILERS is right, o'course I forgot about the port air crap... oops.

böst

It wouldn't hurt anything if I just yanked that damn pump off, would it? It's dragging on the motor, wouldn't it be good to just remove it altogether?

HAILERS

At wide open throttle the relief valve on the acv is wide open at 3500 so it shouldnt matter if the pump is on or not. You could do something simple on the 86-88 and just disconnect one of the two bullet connectors on the bottom of the radiator. That will make the relief valve stay wide open all the time meaning no air going thru anything because its getting dumped overboard all the time. Or take the blue connector off the relief solenoid. Same results. Either takes less than a minute.

böst

Well that's cool, but I have an 89. So, would it hurt anything if I just took the pump out? My friend and I did so on his 90 t2, but I'd like to know the pro/cons. Wouldn't it rid the engine of a little bit of parasitic drag? No more belt, less drag. No pump, less weight. No air pumped not at wot, less backpressure. Please correct me if I'm wrong (or at least before I rip my air pump out).

Turtle's TII

You will be testing at WOT so it does not matter if the pump is functioning normally. I have a wide band A/F meter and I have run the O2 at the downpipe and at the tailpipe and the readings are the same. My stock 87 TII is at 10.5-11:1 at WOT.

Scott 89t2

holy crap that is rich. 11.6 is around where you want it for the street. still a little rich for safty. you'd be making a lot more power with some tuning.

Turtle's TII

I know really fat from the factory, I was thinking about a FCD and removing the first cat to get some more boost. Definately room for improvement (more boost).