C 1500 Truck 2WD V8-350 5.7L (1989)
Fuel: All Technical Service Bulletins
Fuels - Effect of Volatility on Driveability
Number: 93-31-6C
Section: 6C
Date: OCT. 1992
Corporate Bulletin No.: 249128R
ASE No.: A1, A8
Subject:
EFFECT OF FUEL VOLATILITY ON DRIVEABILITY CONDITIONS
Model and Year:
ALL MODEL YEARS, ALL PASSENGER CARS AND TRUCKS
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 92-281-6C, DATED SEPT. 1992. THE 1993 MODEL
YEAR HAS BEEN ADDED. ALL COPIES OF 92-281-6C SHOULD BE DISCARDED.
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:
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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:
Low volatility fuel will not vaporize sufficiently to allow normal combustion.
CORRECTION:
Replace Fuel.
DIAGNOSTIC PROCEDURE:
1.
Perform basic system checks in section 6E of the service manual.
2.
Check for service bulletins which relate to cold driveability issues specific to the problem vehicle.
