can someone explain the root cause of the smog test failure to me ? it sounds like the car was using a California smog test-specific fuel map at the speeds of the test. Wouldn't that make it pass the test, not fail it ?

very cool project anyway.

Yeah doesn’t really make sense, there’s very likely a mechanical issue the LLM “fixed” with a richer fuel mix. But also it’s a 94 XJ the reason the CA map was there was probably because they got abhorrent gas mileage without it.

You can adjust the mixing ratio of fuel and air in a way so that the exhaust has reduced emissions. This will reduce performance of the car but allows the exhaust to pass the emission tests.