What should I do if my Nissan 240SX runs rich?

Answer by  MechMan3 (885)

The mass airflow meter is probably defective, but first check for intake manifold for leaks which is allowing air to "confuse" the computer thinking it needs to richen the mixture. A dry black powder in the exhaust pipe is too much fuel. A 'wet' black pipe says that the engine has blow-by and needs to be rebuilt.

Answer by  bikerbojo (282)

Depends on if it's carburated or injected. If it's carbed then you will need to rejet the carb and reset the air/fuel mix. If it is injected that is done through the computer and you will need an aftermarket fuel management programmer. Install and follow manufacturers instructions.

Answer by  jeffw (173)

Check the fuel pressure at the inlet rail of your fuel injection system. If this is too high you may need a new fuel pump. You may also want to visually inspect your fuel injectors. Some auto repair stores can test them to see if they are good if you take them in.

Answer by  Amber40 (24961)

Tune the engine to run one less fuel with some software. If it's not off by much you may be able to just improve air flow into the engine engine to lean out the mixture.