SW L4-1.9L DOHC VIN 7 (1993)
One reason most of today's engines do not need premium gasoline is the Electronic Ignition Control system. The ignition control system's knock sensor
(detonation sensor) reports any pinging to the Engine Control Module (ECM), which retards ignition timing. Delaying the spark produces less build-up
of heat and pressure - so the end gas does not explode, but burns properly. However, retarding the timing reduces engine efficiency; so the system
operates only when necessary.
Another way to reduce knock is to use combinations of the basic hydrocarbons in fuel that offer more resistance to knock. Adding lead to the gasoline
will also increase the octane but fouls catalytic converters. Another way to increase octane is to add "oxygenates," that is, chemicals composed of
hydrogen, carbon. and at least one oxygen atom. Increasing the octane enables the fuel to withstand greater pressure and heat. Under normal conditions,
regular unleaded 87 octane fuel is sufficient for today's vehicles.
REID VAPOR PRESSURE (RVP) TEST
The Reid Vapor Pressure (RVP) test indicates the fuel's tendency to evaporate early. The test also indicates how the engine may perform during a cold
start and warm-up. The higher the RVP the higher the volatility.
RVP is measured using a Reid Vapor Pressure Tester. A gasoline sample at 32°F is placed in a sealed container that is attached to a pressure gage. The
container is then placed in a 100°F water bath for two to five minutes. The pressure gage reads the pressure in pounds per square inch (psi) exerted by
the vaporized fuel within the sealed container. This test can be performed using the Saturn Service Fuel Test Kit SA9213NE (or equivalent).
According to more stringent standards effective on June 1, 1992, except in Alaska and Hawaii, the EPA limits RVP to 9.0 psi maximum between May
and September 15. In "ozone non-attainment" in the areas in the southern and western U.S., the EPA limits RVP to 7.8 psi maximum between June 1 and
September 15. The EPA permits these maximum vapor pressures to be 1.0 psi higher for gasoline-ethanol blends that contain (by volume) 9 to 10%
ethanol.
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