4Runner running rich?

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I have a '91 4Runner that I put a used engine in last year. It runs well. It also got a new cat at the same time as the engine. During high-load conditions, such as going up hills, if I have the back window open, I get that rotten-egg type smell. Therefore, I assume I'm running rich at open throttle conditions. Is this something I can fix?
 
Are you getting a check engine light? If not, you are just smelling the cat doing its thing......Slightly richer mixture is normal at WOT. You might switch fuel brand.......But a better idea is to stop driving with the back window open......that is a good way to get carbon monoxide poisoning.
 
It's normal at WOT for an OBD car to go into open loop and run rich to keep temperatures down. Perhaps the cat can't keep up, but unless you get a CEL I wouldn't worry too much about it.
 
Originally Posted By: ARCOgraphite
Make sute the exhaust is super tight ( no leaks) up to the #1 O2 sensor.
No misfire?


No misfires, but I'll check the exhaust for sure.
 
If your truck is so old that the engine had to be replaced, then I am sure the O2 sensor is no longer accurate.

Also, sometimes the coolant temperature sensor will fail, but because it fails at a temperature that can happen in normal driving, no error code for coolant temperature is set. Below a certain coolant temperature, the car will run in open loop, and that is why the engine would run excessively rich.
 
Originally Posted By: artificialist
If your truck is so old that the engine had to be replaced, then I am sure the O2 sensor is no longer accurate.

Also, sometimes the coolant temperature sensor will fail, but because it fails at a temperature that can happen in normal driving, no error code for coolant temperature is set. Below a certain coolant temperature, the car will run in open loop, and that is why the engine would run excessively rich.


spot on for Toyos from those years,
I will add the cold weather sensor (??? someone help me here pls), might be bad also leading to rich mix.
also, make sure all cylinders are firing
 
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