1980 Ford F150 Failed esmissions (CO) under load
During acceleration, the engine momentarily drops out of closed loop and receives a richer fuel mixture for more power. During this time (depending on the system), the MAP or Airflow Sensor and the TPS sensor play critical roles in controlling the fuel mixture.
Most fuel-injected engines have either a throttle position sensor or switch that indicates when the engine is at idle. When this device indicates that the engine is no longer at idle, the on time of the injectors is increased to temporarily richen the fuel mixture. The same thing happens any time the engine comes under load and manifold vacuum drops. The MAP sensor tells the computer the engine is under load, and the computer responds by adding more fuel.
It is normal to see some spikes in CO during acceleration, but unusually high CO readings indicates that the fuel mixture is too rich. Possible causes might include:
Flooded charcoal canister or a leaky purge valve;
Leaky power valve (older carbureted engines);
Defective mass airflow (MAF) sensor, manifold absolute pressure (MAP) sensor, or vane airflow meter (VAF); or
Defective throttle position sensor
Monday, May 11th, 2009 AT 7:57 PM