Gen 2 – Inconsistent RPM at Set throttle/Intermittent P0420



I don’t see engine temp, but based on the data it was in closed loop and I will assume the engine was warmed up.

Looking at the logs, I believe you have an issue with fueling. The engine is knocking, sometimes pretty bad, and the computer is adjusting for it. Most of the fuel correction is on bank 1.

Check the fuel filter in the tank. It may need replacement. If you have a way to check fuel pressure and flow, it should be about 45 psi idle with the pressure regulator vacuum hose off the regulator. No lower than 41. With the hose connected, 31-34 psi.

Do you know how old the AF sensors are?

Check your main ground cable between the battery post and the end of the cable down by the starter. With a multimeter set on Ohms, you should have 0.0 Ohm end to end. If not, either get a new cable set and positive clamp from Subaru, or get a 4 gauge cable with eyelets on both ends and add it from the negative clamp to the AC/Alt bracket. You can use the top AC bolt.

If you post any more logs after making corrections to the car, add ECT. Get rid of fuel tank pressure. Knock off the engine load calculated and 1-byte; keep relative. The less it’s recording the better as far as speed and the data curve go.

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