Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1999METRO L4-079 1.3L VIN 2 MFIREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSCAN TOOL TESTING AND PROCEDURESSCAN TOOL DATA DEFINITIONS - POWERTRAIN SYSTEMSLONG TERM FT
1999 Chevrolet Metro L4-079 1.3L VIN 2 MFI
Long Term FT
1999 Chevrolet Metro L4-079 1.3L VIN 2 MFISECTION Long Term FT
The scan tool displays a positive or negative percentage. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long-term correction in the fuel delivery. A value of 0% indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0% indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A positive value significantly greater than 0% indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.
The scan tool displays counts. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long-term correction of fuel delivery. A value of 0% indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A value significantly below 128 indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A value significantly greater than 128 indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.
The scan tool displays counts. The PCM derives the Long Term Fuel Trim (FT) from the Short Term FT value. The Long Term FT represents a long-term correction of fuel delivery. A value of 0% indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A value significantly below 128 indicates that the fuel system is rich and the PCM is reducing fuel delivery (decreased injector pulse width). A value significantly greater than 128 indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.