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

Fig 1: Driveability Concerns Table

Courtesy of GENERAL MOTORS CORP.

Diagnostic Hints 

• Start diagnosis by verifying the complaint. Keep the vehicle overnight before verifying a cold driveability problem.
• Remember that the symptom(s) may indicate a fuel delivery/pressure or fuel control problem.
• If the engine is functioning properly, suspect fuel volatility/fuel quality.
  • Determine if the customer is using premium grade fuel. If so, suggest trying a different brand of fuel or regular 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 the customers that it may require more than one tankful of a different brand of fuel to correct a fuel quality problem.
  • Determine if the customer has old fuel in the 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 the fuel volatility wrong for the weather.