How could hundreds of clearings of the OBD codes cause the catalytic I/M readiness monitor to set?

[Xeno]

It will definitely shut off the fuel - if nothing else. If you have fuel but no spark you will be flooding the cat with raw fuel. That's bad.

[Michael]

I wonder what it does because it's impossible to shut off the fuel since there is only one intake manifold and the injectors inject fuel into it just like a carburetor would have, only a bit closer to the cylinders.

If they shut down the fuel there will ALWAYS be fuel getting into the cylinders, but maybe the baffles are designed that one injector "mostly" injects into one cylinder for cars that aren't direct injected (which is most cars that are NOT direct fuel injected).

[Xeno]

Should mention, I suppose, that it only apples to sequential injection with cylinder specific misfire monitors, V8 & V6 engines typically. Gang fired injection systems just might not run so well with *half* the cylinders getting no injection pulses. 😉 For the rest it's goodbye to the cat if the vehicle continues to be driven, or it goes into some form of severe limp mode and that pretty much forces rectification of the issue.

[trader_4]

Wow there Pilgrim. If there isn't a downstream sensor, then how can the computer know that the catalytic converter isn't working? I've never seen or heard of a modern car that doesn't have a downstream sensor. Measuring the O2 difference between upstream and down is how they monitor the cat converter.

I agree you typically have that as an indication of a bad O2 sensor, but it might be possible that a bad O2 sensor could affect the accuracy of monitoring the cat converter. Also possible that the water affected the O2 sensors, not the converter.

It's not just a whim, you're getting a code that depends on the accuracy of those sensors. How old are they? You think the downstream doesn't exist, so that one you haven't replaced, could be original. They typically last 100K or so. Replacing that for $50 seems very logical to me.

Yes, if the failure is bad enough, but I would think it's possible it could not register accurately too.

[trader_4]

Not any modern cars I've dealt with. They have an injector for each cylinder, for among other reasons, meeting emissions and protecting the cat converter. Like Mike said, if a misfire is detected on one cylinder, the computer shuts down the injector on that cylinder to prevent raw gas going into the exhaust.

[trader_4]

How many injectors are there? My bet it's a 4 cylinder and there are 4. That's how they shut down a misfiring cylinder, shutting off the fuel. If there were not one for each cylinder, what would happen? If there was one injector for two cylinders, they would have to shut down two and that wouldn't work very well. They have to shut off fuel, for emissions and because raw fuel would wreck the cat converter.

[Scott Dorsey]

It's bad in the sense that it will burn up the converter but... that might be an advantage if you have a gunked-up converter. At least if it doesn't explode.

--scott

[Hiram T Schwantz]

On Sun, 23 Apr 2023 23:00:56 +0530, mike posted for all of us to digest...

Sni9pped for your pleasure!

Is that you Arlen?