Any home tests, or indications that could be used to tell?

 

looking at the exhaust tips for more discoloration.

 

The check engine light will illuminate in modern OBD 2 equipped vehicles.

Jens

 

checking the black shit on the exhaust

 

What do you mean by "too rich"?

 

too rich means too much fuel for the amount of air going into the engine. Too lean is the opposite, too little fuel for the amount of air going into the engine. Being lean is more dangerous than being rich. Being lean will cause higher exhaust gas temps. But being too rich can cost you power.