Hyundai Sonata 1991 Shop Manual page 260

MPI SYSTEM
7. Measure the fuel pressure when the vacuum hose is con-
nected to the pressure regulator.
Standard value .
270 kPa (2.75 kg/cm', 39 psi)
8.
If the results of the measurements made in steps (6) and
(7) are not within the standard value, use the table below
to determine the probable cause, and then make the
necessary repair.
Condition Probable cause Remedy
Fuel pressure too low a. Restricted fuel filter. a. Replace fuel filter
b. Fuel leakage to the return side, caused
b. Replace fuel pressure regulator.
by poor seating of the valve within the
fuel-pressure regulator
c. Low discharge pressure of the fuel pump c. Replace fuel pump
Fuel pressure too high
a. Sticking valve within the fuel-pressure a. Replace fuel pressure regulator
regulator
b. Restricted or bent fuel return hose or pipe. b. Repair or replace hose or pipe.
There is no difference in a. Restricted, or damaged vacuum hose or a. Repair or replace the vacuum
fuel pressure between
fitting hose or fitting
when the vacuum hose b. Sticking valve within the fuel-pressure b. Replace fuel pressure regulator
is connected and when regulator, or poor seating
it is not.
9. Stop the engine and check for a change in the fuel pressure
gauge reading, which should not drop.
If the gauge indication drops, observe the rate of drop.
Determine and remove the causes according to the following
table.
Condition
Probable cause
Remedy
Fuel pressure drops
a. Injector leakage a. Replace injector
slowly after engine is
stopped
Fuel pressure drops im-
a. The check valve within the fuel pump is a. Replace fuel pump
mediately after engine is
not closed
stopped
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