Fuel Metering System

Some failures of the fuel metering system will result in an "Engine Cranks But Will Not Run" symptom. If this condition exists, refer to the Cranks But Will Not Run chart. This chart will determine if the problem is caused by the Ignition System, the Powertrain Control Module (PCM), or the fuel pump electrical circuit. Refer to Fuel Delivery and Air Induction / Diagrams for the fuel system wiring.

If there is a fuel delivery problem, refer to Fuel Delivery and Air Induction / 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 long term fuel trim values are greater than +23%, refer to DTC PO131, DTC P0151, DTC P0171, and DTC 1171 for items which can cause a lean HO2S signal.