Fleetwood V8-368 6.0L VIN 9 FI (1982)
Fuel: Customer Interest
Fuels - Effect of Volatility On Driveability Conditions
NO.:
93-1-9
DATE:
Nov. 1992
GROUP:
6
CORP. NO.:
249128R
SUBJECT:
INFORMATION ON THE EFFECT OF FUEL VOLATILITY ON DRIVEABILITY CONDITIONS ON ALL YEARS, ALL MODELS
Background Information
Recent changes in EPA regulations have effectively lowered the maximum allowable fuel volatility. Volatility is the ability of gasoline to change from a
liquid to a vapor. It directly affects the amount of evaporative emissions released from the fuel. Lower volatility results in fewer unburned hydrocarbons
being released into the atmosphere during fuel storage and transfer. Unfortunately, reducing fuel volatility can pause problems during cold engine
operation since low temperatures limit the ability of fuel to vaporize and burn.
The two terms used to describe volatility characteristics are:
Distillation Curve:
^
The distillation curve is 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~F) are known as "light ends" and are essential for good cold engine performance. "Heavy
ends" boil at about 300~F and 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) vaporized fuel exerts within a sealed container when heated to 100~F The higher the RVP the higher the fuel volatility.
While RVP may be easily tested in the field, fuels containing 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
lower volatility). This can make cold driveability as major a problem during summer months as during winter. There may be additional variation in the
volatility of pump gasoline caused by the differences in fuel manufacturers, blends, and storage times. As fuel volatility is lowered as required by EPA
regulations, variations among further reduce volatility and become a critical factor which may severely affect cold engine performance. No matter how
thoroughly the relationship between fuel quality and cold driveability is understood, eliminating fuel quality as a cause can be difficult due to the
following:
TOOLS WHICH TEST FUEL VOLATILITY MEASURE ONLY RVP NOT THE DISTILLATION CURVE.
^
The distillation curve has a greater effect on cold driveability than RVT.
THE CUSTOMER MAY PERCEIVE DISCUSSING FUEL QUALITY 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 after the vehicle has been refueled several times with quality gasoline.
Customer Concerns
CONDITION:
Poor Cold Engine Operation symptoms may include - hard start/extended crank, stalling, backfiring, hesitation, rough idle, detonation, and/or lack of
power.
POSSIBLE CAUSE:
