Skylark L4-138 2.3L DOHC VIN D MFI QUAD 4 (1989)
Fuel: Technical Service Bulletins
Fuel - Effect of Fuel Volatility On Driveability
Bulletin
92-6E-23
Date
Sept. '92
Ref. No.
92-273-6E
Corp. Ref. No.
249128
SUBJECT:
INFORMATION ON THE EFFECT OF FUEL VOLATILITY ON DRIVEABILITY CONDITIONS
MODELS AFFECTED:
ALL YEARS - ALL MODELS
BACKGROUND INFORMATION
Recent changes in EPA regulations have effectively lowered the maximum allowable fuel volatility. Volatility, which can be defined as a gasoline's
ability to change from a liquid to a vapor, directly affects the amount of evaporative emissions produced by the fuel. Higher volatility means that more
unburned hydrocarbons will be released into the atmosphere. Unfortunately, reducing fuel volatility can cause problems during cold engine operation
when low temperatures impede the fuel's ability to vaporize and burn.
Two terms are often used to describe volatility characteristics. These are:
-
Distillation Curve
A graph showing the relationship between temperature and the percentage of fuel evaporated. The fuel components that boil at relatively low
temperatures (below about 90 degrees F) are known as the "light ends", and are essential for good cold engine performance. The "heavy ends",
which begin to boil at about 300 degrees F, contain the most energy but are more difficult to burn. Laboratory analysis is usually required to
determine the distillation curve of a gasoline sample.
-
Reid Vapor Pressure (RVP)
RVP is the pressure (psi) that vaporized fuel exerts within a sealed container as it is heated to 100 degrees F. The higher the RVP, the higher the
fuel volatility. While RVP is readily tested in the field, fuels of the same RVP can have different distillation curves and cold driveability
characteristics.
Fuel volatility will vary depending on geographic location and time of year (fuel intended to be used in higher ambient conditions is formulated with less
volatility). This can make cold driveability as big a problem during summer months as during the winter. There may be additional variation in the
volatility characteristics of pump gasoline, caused by the differences in fuel manufacturers, blends and storage times. As EPA fuel volatility standards are
lowered, variations between fuels (which may further reduce volatility) becomes a critical factor influencing cold engine performance.
No matter how thoroughly the relationship between fuel quality and cold driveability is understood, eliminating fuel quality as an issue can be difficult,
because:
TOOLS WHICH TEST FUEL VOLATILITY MEASURE ONLY RVP, NOT THE DISTILLATION CURVE.
-
The distillation curve has a greater effect on cold driveability than RVP.
THE CUSTOMER MAY PERCEIVE RAISING THE FUEL QUALITY ISSUE AS AN ATTEMPT TO EVADE HIS PROBLEM.
-
This may cause difficulty in getting accurate fuel usage information.
WATER, AND OTHER TYPES OF FUEL CONTAMINATION, MAY CAUSE CONTINUED DRIVEABILITY COMPLAINTS.
-
The problem symptoms may remain even though the vehicle has been refueled several times with a quality gasoline.
CUSTOMER CONCERNS
CONDITION:
Poor Cold Engine Operation, symptoms may include; hard start/extended crank, stalling, backfiring, hesitation and/or lack of power.
POSSIBLE CAUSE:
