Prizm L4-1600cc 1.6L DOHC VIN 6 (1990)
Chart A-7
CIRCUIT DESCRIPTION:
The fuel pump delivers fuel to the fuel rail and injectors, where the system pressure is controlled from 262 to 303 kPa (38 to 44 psi) by the pressure
regulator. Excess fuel is returned to the fuel tank. When the engine is stopped, the pump can be energized by applying battery voltage to the test terminal
located in the engine compartment.
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
5.
Pressure less than 262 kPa (38 psi) may be caused by one of two problems. The system will be running lean and may set Code 25. Also, hard cold
starting and overall poor performance is possible. Restricted flow is causing a pressure drop. Normally, a vehicle with a fuel pressure loss at idle
will not be driveable. However, if the pressure drop occurs only while driving, the engine will surge and then stop as pressure begins to drop
rapidly.
6.
Restricting the fuel return line allows the fuel pump to build above regulated pressure. When battery voltage is applied to the fuel pump test
terminal, pressure should be above 450 kPa (65 psi).
7.
This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.
DIAGNOSTIC AIDS:
Improper fuel system pressure may contribute to one or all of the following symptoms:
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Cranks but won't run.
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Cutting out (May feel like ignition problem).
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Hesitation, loss of power or poor fuel economy, See: Computers and Control Systems/Testing and Inspection
