Bad Catalytic Converter?

[uwbradley]

My 91 Mazda Navajo is throwing a Code 41, and I have replaced the O2 sensor twice. I have also replaced the MAF, and I still get the same code. Would a bad cat possibly lead the O2 sensor to throw codes, since it could be clogged? Does a bad cat let off a smell, or some other signs that could point to be it being bad?

Thanks-
Brad

 

[MrShorty]

Bad cat will usually show up as low engine vacuum, too. I wouldn't completely discount the possibility of a bad cat, but it's usually not the cause of a 41. Things that usually cause a 41, not in any particular order:
1) Bad O2 sensor
2) Bad wiring between O2 sensor and PCM
3) Bad PCM ground
4) Low fuel pressure
5) misfire
6) Exhaust leak upstream of O2 sensor.
7) cold engine during KEOR test (if KOER code).
8) vacuum leak
9) and I'm sure there are others.
O2 sensor codes can be among the more difficult to diagnose.
Do you get a 41 both for the KOER test and continuous memory, or does it pass the KOER test?
Among the first things the manuals say to do with an O2 sensor code is to check the fuel pressure/fuel delivery? What's your fuel pressure?

 

[uwbradley]

Well, this is what the shop has told me. I have never actually read the codes myself.

As for the fuel pressure, that was the last thing that the shop replaced was the fuel pump because he said that the pressure wasn't high enough.

So, with that out of the way, should I have the exhaust system checked?

Brad

 

[MrShorty]

If you like, you can have the exhaust system checked. Many times the inspection is free in the hopes that they can find something wrong.
Among the question I would ask:
Did the new fuel pump rectify the low fuel rail pressure?
Has the shop verified the wiring between the O2 sensor and the computer?
Is the 41 both a KOER code and a continuous memory code or not?

 

[dalefanatic38]

if the cat is bad it will smell like rotten eggs.

 

[uwbradley]

Shorty-

Thanks! I am gonna get this stuff looked at today. Thanks for the questions to ask!

Brad