Hi all a little help.
have spent hours looking and can not find the normal voltage my barometric pressure sensor should be reading. engine is over fuelling and back fires when you whip the throttle (which failed emissions on MOT, ppm over 1400) have been down every road Cat is working fine an with new 02 and coils plugs ect, now looking at the baro as 5v looks way to high

It's currently sat at 5v and reads 14psi and i dam well know it's not 14psi out side of we would all be dead.

 

14psi is actually normal atmospheric pressure 14psi of BOOST is double atmospheric pressure.


Have you addressed the basics yet? Coils, plugs and wires fail regularly and should be replaced regularly, and if they fail it will easily cause this.

 

Have been down the lot! even the injectors have been changed.

All I know is if I plug into any normal car it would be at 1000 mb which is 1psi.
This barometric pressure sensor is in fact a manifold absolute pressure sensor being used unconnected to the manifold to create a barometric sensor, with that in mind I think the normal reading may or may not be a little funny.

 

No you are right just been looking and 1000mb is 14psi. confusing myself again as yes 14psi of boost would be 2X atmospheric

 

What are your AFRs at idle and during the test? They are reported over the OBD2 port, both commanded AFR and actual AFR. If the AFR is what it should be, then you aren't over-fueling. If it's rich, then you are. The rotary always dumps a bit of unburnt gas into the exhaust when you let off the throttle, the sharper you let off, the more gas will get dumped in. If you run catless, this almost always produces a backfire or flames from the tail pipe. So if your AFRs are good, I would suspect that your cat is failing.

 

Been playing some more today and osiloskoped o2 sensor in the cat while driving and in a piston engine we would of said the cat was gone but it's not flagged up any faults which it should of done.
Big problem all along is that fully know how to diagnose any normal car and know what am looking for, but don't get to do enough on the rotarys and can't find the pin data and info to show on them anywhere.
Got new cat on order just hope it sorts it, would love to take it out but no way would it pass a mot test.

 

FYI, the RX-8's ECU can't identify a failing cat.


It's supposed to, but it isn't a sure thing, and you can not rely on the ECU to be able to do it. Most RX-8s can take weeks or months after removing a cat before the ECU figures out that there isn't a cat any more, and reseting the ECU can make it take that long again. If you actually have even a bit of cat element still left, it can prevent it from recognizing it entirely.

 

As if that's bad!!

 

Not for us enthusiasts

But it means that your cat can be bad and the ECU not give a single sign of it. My cat clogged around 55,000 miles from misfires and damaged an O2 sensor and my engine and never once triggered a CEL or test failure.