Initial Inspection and Diagnostic Overview

Always start with an On-Board Diagnostic System Check. This will reduce diagnosis time, and prevent unnecessary parts replacement.
If a malfunction occurs in the fuel metering system, it usually results in either a rich or lean exhaust condition. This condition is sensed by the Oxygen sensor and causes the ECM to change the fuel calculation (injector pulse width). The change made to the fuel calculation is indicated by a change in the integrator and block learn values, which can be monitored by a "Scan" tool. A short term change to the fuel calculation is indicated by the integrator value, while a long term change is indicated by the block learn value. Average integrator and block learn values are around 128, but vary slightly from engine to engine.

IMPORTANT:
- When using "Scan" tool to observe integrator and block learn values, remember that if the system is in control, no action is required unless a driveability symptom is present. Listed below are examples of lean and rich conditions with the system in control and out of control.
- A momentary lean condition (system is in control) will appear on "Scan" tool as:
- Integrator value above 128 (adding fuel)
- Block learn value around 128
- A long term lean condition (system is in control) will appear on "Scan" tool as:
- Integrator value around 128
- Block learn value above 128 (added fuel)
- A long term lean condition (system is out of control) will appear on "Scan" tool as:
- Integrator value well above 128 (adding fuel)
- Block learn value well above 128 (added fuel)
If both the integrator and block learn values are fixed well above 128, see DTC 44, for items which can cause a lean system.
- A momentary rich condition (system is in control) will appear on "Scan" tool as:
- Integrator value less than 128 (reducing fuel)
- Block learn value around 128
- A long term rich condition (system is in control) will appear on "Scan" tool as:
- Integrator value around 128
- Block learn value less than 128 (reduced fuel)
- A long term rich condition (system is out of control) will appear on "Scan" tool as:
- Integrator value much less than 128 (reducing fuel)
- Block learn value much less than 128 (reduced fuel)
If the integrator and block learn values are fixed well below 128, see DTC 45, for items which can cause the fuel system to run rich. If a driveability symptom exists, refer to the particular symptom in "Symptoms" for additional items to check.