DRIVEABILITY Symptoms Versus Fuel Quality (Engine Systems Functioning Properly): Notes

Fig 1: Listing Driveability Symptoms & Causes

Courtesy of GENERAL MOTORS CORP.

Diagnostic Hints

Start diagnosis by verifying complaint. Keep vehicle overnight before verifying a cold driveability problem.
Remember that the symptom(s) may indicate a fuel delivery/pressure or fuel control problem. Use DTC codes and fuel system diagnostic procedures in SELF-DIAGNOSTICS - 3.0L or FUEL SYSTEMS (GASOLINE) for diagnosis.
If engine is functioning properly, suspect fuel volatility/fuel quality.
- Determine if customer is using premium grade fuel. If so, suggest trying a different brand of fuel or regular unleaded fuel except when a premium-grade is recommended because of operating conditions. Some premium grade gasolines may actually cause cold engine driveability problems because of their lower volatility in the warm-up range. Inform customers that it may require more than one tankful of a different brand of fuel to correct a fuel quality problem.
- Determine if customer has old fuel in tank. If so, the volatility may be too low because the "light-ends" have evaporated.
- Consider the possibility that an unseasonable cold snap has made fuel volatility wrong for the weather.