Fuel Metering System
Some failures of this system will result in an Engine Cranks But Will Not Run symptom. If this condition exists, refer to Engine Cranks but Does Not Run . This diagnostic will determine if the problem is caused by the ignition system, the PCM, or the fuel pump electrical circuit.
Refer to
Fuel Tank
or
Fuel Tank and Fuel Pump Resistor
for the fuel system wiring schematic.
If there is a fuel delivery problem, refer to Fuel System Pressure Test (VIN K) or Fuel System Pressure Test (VIN 1) . This diagnostics are for 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 signa,l or in a lean HO2S signal. This condition is indicated by the HO2S voltage, which will cause the PCM to change the fuel calculation, indicated by the fuel injector pulse width, based on the HO2S reading. Changes 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 approximately 0% for a lean HO2S signal. The PCM will add fuel, resulting in a fuel trim value that is more than 0%. For a rich HO2S signal, the PCM will take away fuel, resulting in a fuel trim value that is less than 0%. Some variations in the fuel trim values are normal due to the power train design. If the fuel trim values are significantly higher or lower than 0%, refer to DTC P0171 Fuel Trim System Lean or DTC P0172 Fuel Trim System Rich .
Idle Air Control Valve
The scan tool displays IAC pintle position in counts. "0" counts indicates that the PCM is commanding the IAC pintle to be driven all the way into a fully-seated position. This condition is usually caused by a vacuum leak.
The higher the number of counts, the more air is being commanded to bypass the IAC pintle. Refer to Idle Air Control (IAC) System Diagnosis in order to diagnose the IAC system. Refer to Rough, Unstable, or Incorrect Idle and Stalling in Symptoms for other possible causes of idle problems.
Fuel System Pressure Test
A fuel system pressure test is part of several of the diagnostic charts and symptom checks. To perform this test, refer to Fuel System Pressure Test (VIN K) or Fuel System Pressure Test (VIN 1) .
