Originally posted by projectSHO89:
Tony,

Chicken... Egg... Chicken ... Egg ...

Which came first?

You're assuming that, in your case, that the cat codes caused the poor fuel economy.

More likely, the conditions that caused the poor fuel economy, ie, misfire, lazy upstream O2 sensor, or whatever caused an excessively rich exhaust, caused the cat to fail due to all the unburned fuel that was dumped into it. This then set the efficiency codes..

Makes more sense...doesn't it?..



Makes good sense.

Now, how about this? Cats failed (all things breakdown eventually) and plugged up causing the cats and engine not to work at full efficiency (due to increase in exhaust backpressure) i.e not enough vacuum in intake, with resulting loss in fuel economy and performance, causing CELs to come on. (other codes too besides the P0420 or P0430)

Once again, chicken or the egg?

Yes, I will accept that the P0420 or P0430 will not put the PCM in limp mode (even though I don't have any documentation that says that). However, if you have the P0420 or P0430, chances are the car will run crappy eventually (when, after the CEL turns on, is anybody's guess).


"Always do the cheap and easy ones first." 1996 V6 ATX 96K miles