Coupe L4-1.9L DOHC VIN 7 (1994)
DIAGNOSING FUEL QUALITY PROBLEMS
Symptoms
A fuel-quality problem may be indicated by the following driveability symptoms:
^
spark knock/detonation
^
hard cold start and garage stalls
^
poor cold performance
^
tip - in hesitation, sag, or stumble (momentary lack of response during initial acceleration)
^
surges and/or Chuggles
^
lack of power, sluggish, or spongy
^
cut out or misses
^
rough/unstable idle
VOLATILITY
Volatility is a gasoline's tendency to change from a liquid to a vapor. Volatility is crucial to engine performance. Liquid gasoline will not burn; only
vaporized gasoline burns. Once liquid fuel is injected into an intake port and mixed with air, some of it should start evaporating immediately.
Any liquid's rate of evaporation changes with temperature. Temperatures in an engine vary widely. During operation, the combustion chamber
temperatures may rise to more than 822°C (1500°F). Before start-up, on a very cold morning, the temperature may be zero. To burn well across the
broad range, a fuel must consist of a mixture of hydrocarbons that vaporize at different temperatures.
The hydrocarbons consisting of smaller molecules vaporize at lower temperatures and those consisting of larger molecules vaporize at higher
temperatures. The easily vaporized hydrocarbons, which are easy to burn, are called the "light-ends." They help with quick starts when the engine is cold.
The less volatile "heavy-ends" contribute more to engine power, but because they are harder to burn, they can coat the cylinder walls without burning
and in extreme cases may dilute the oil in the crankcase.
Lower volatility is desirable in the summer to prevent excessive premature evaporation of the fuel. In the winter, high volatility is desirable because the
fuel must vaporize quickly for cold starts and good cold drive ability.
