[Surfnfisher]

2005 220k
I’m getting poor mileage in my sienna. Sometimes i smell fuel. Obd says cats are bad.
question. Can I use any after market cat for my sienna?
Do bad cats contribute to poor mileage?
Will the bad cats have a fuel smell?
Thanks for the help

 

[circus]

My 99 was getting poor mileage and the OBD said cats were bad. No gas smell. Once the reason for the poor fuel mileage was found the catalysts were fine.

Do bad cats contribute to poor mileage?

Poor mileage contribute to bad cats.

 

[sixto]

Are you calculating fuel mileage after filing the tank or going by the computer display? What’s the fuel mileage you consider bad?

Bad cats can affect fuel mileage but I’d think the performance hit would be more obvious.

Scan live data, particularly engine temp, MAF readings, oxygen sensor readings and fuel trims. Should point you in the right direction.

Sixto
‘04 LE FWD 207K miles

 

[BillG]

Bad cat codes never mean bad cats unless your other issue which triggers the code(s) goes on long enough to saturate the cat(s). Find the cause of the combustion efficiency problem and the codes go away.

 

[Surfnfisher]

Different mechanics over the years have stated cats are bad. Cel comes on every 150 or so miles after clearing. I’m not required to smog so I just keep driving.

 

[Roader]

Sometimes i smell fuel...Will the bad cats have a fuel smell?

No. Chase down that smell. You don't want any fuel injection piping leaks as it could cause a fire. If there are no external leaks and you're not getting any EVAP codes, check out fuel trim threads on this forum to see if the engine is running rich.

 

[siennadan]

My 2004 had both a dirty MAF sensor and a faulty thermostat that was open too much depressing efficiency. Does your engine temperature on your dash display stay pretty low? Easy way to check on the thermostat is said to be to remove the radiator cap from a cold engine and see when flow starts. You could also use a electronic kitchen thermometer to help you follow. For the V-6 engine in my Sienna (3MZ-FE), when warmed up, temp should be above 176 degrees F.