Fuel Metering System
Fuel Metering System CheckSome failures of the fuel metering system will result in an Engine Cranks But Will Not Run symptom. If this condition exists, refer to the Engine Cranks But Will Not Run chart. Refer Diagnosis By Symptom.
This chart will determine if the problem is caused by the ignition system, the PCM, or the fuel pump electrical circuit. For the fuel system wiring schematic, refer to Fuel System Electrical Test.
If there is a fuel delivery problem, refer to Fuel System Diagnosis, which diagnoses the fuel injectors, the fuel pressure regulator, and the fuel pump.
If a malfunction occurs in the fuel metering system, it usually results in either a rich HO2S signal or a lean HO2S signal. This condition is indicated by the HO2S voltage, which causes the PCM to change the fuel calculation (fuel injector pulse width) based on the HO2S reading. Changes made to the fuel calculation will be indicated by a change in the long term fuel trim values which can be monitored with a scan tool. Ideal long term fuel trim values are around 0%; for a lean HO2S signal, the PCM will add fuel, resulting in a fuel trim value above 0%. Some variations in fuel trim values are normal because all engines are not exactly the same. If the evaporative emission canister purge is ON, the long term fuel trim may be as low as -38%. If the fuel trim values are greater than +23%, for items which can cause a lean HO2S signal, refer to DTC P0131, DTC P0151, DTC P0171 and DTC 1171.