For fuel injected engines, the fuel pump is powered through the ASD relay in the power module and a 20A fuse on the fuse panel. The ASD relay is turned on for one second when the ignition is in the "on" position to pressurize the fuel system. See the Automatic Shut Down (ASD) Relay page for more information on the behavior of the ASD relay.
Throttle body injected (TBI) and multi-port injected (MPI) turbo engines use a fuel pump that is inside the fuel tank. This way, the pump is instantly primed, does not pump air through the system, and is kept cool by the fuel. Shelby turbo engines on the L-body vehicles feature a dual-pump system with one pump in the tank and the other mounted near the fuel filter. The TBI engine fuel system will generate 14.5 psi relative to intake pressure (34 psi for 1984-1985 systems), while the turbo engine fuel systems generate 55 psi relative to intake pressure. See the Diagnosing Your Fuel System page for more information.
On 1988 and later models, if 12V is not detected on the output of the ASD relay when the relay is turned on, a fault code 42 is stored.
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Copyright © 1996-2003 Russ W. Knize.