I'll can have a shot at answering that...

Whether you've got a PCIII, PCV, Kev Mod, Nitro-X (or nothing at all) the air/fuel ratio will be stuck at 14.7:1 in the closed loop (unless of course you've already got the Dyjet O2 eliminator fitted). The problem is when you've sorted out the open loop fuelling with your PCV map to get a more respectable 13.2-13.6:1 there is a massive step in the mixture when the change occurs between closed and open loop; this is where the problems lie. By fitting Kev's O2 controller, which permanently fixes the ratio at 13.6:1, this step in fuel/air ratio between open and closed loops disappears, smoothing things out greatly.

It will definitely make a difference with a PCV as it will bring the closed loop fuelling much more in line with you map stored in the PCV.

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