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.

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.

Safety Warning

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