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ON-VEHICLE SERVICE
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MULTIPORT FUEL INJECTION (MFI) <3.0L>
13B-681
8. Measure fuel pressure while the engine is running at idle.
Standard value: Approximately 270 kPa (38 psi) at
curb idle
9. Disconnect the vacuum hose (blue stripe) from the fuel
pressure regulator and measure fuel pressure with the hose
end closed with your finger.
Standard value: 330
−
350 kPa (47
−
50 psi) at curb idle
10.Check to see that fuel pressure at idle does not drop even
after the engine has been revved several times.
11.Revving the engine repeatedly, hold the fuel return hose
lightly with your fingers to feel that fuel pressure is present in
the return hose.
NOTE: If the fuel flow rate is low, there will be no fuel pres-
sure in the return hose.
12.If any of fuel pressure measured in steps 8 to 11 is out of
specification, troubleshoot and repair according to the table
below.
13.Stop the engine and observe fuel pressure gauge reading. It
is normal if the reading does not drop within two minutes. If it
does, observe the rate of drop and troubleshoot and repair
according to the table below. Start, then stop the engine.
(1) Squeeze the fuel return line closed to confirm leak-down
occurs from defective fuel pressure regulator.
(2) Squeeze the fuel supply line closed to confirm leak-down
occurs from defective fuel pump check valve.
(3) If pressure continues to drop with both fuel lines
squeezed closed, injector (s) are leaking.
SYMPTOM
PROBABLE CAUSE
REMEDY
•
Fuel pressure too low
•
Fuel pressure drops after racing
•
No fuel pressure in fuel return
hose
Clogged fuel filter
Replace fuel filter
Fuel leaking to return side due to
poor fuel regulator valve seating or
settled spring
Replace fuel pressure regulator
Low fuel pump delivery pressure
Replace fuel pump
Fuel pressure too high
Binding valve in fuel pressure
regulator
Replace fuel pressure regulator
Clogged fuel return hose or pipe
Clean or replace hose or pipe
Same fuel pressure when vacuum
hose is connected and when
disconnected
Damaged vacuum hose or
clogged nipple
Replace vacuum hose or clean
nipple
Defective fuel pressure regulator
Replace fuel pressure regulator
SYMPTOM
PROBABLE CAUSE
REMEDY
Fuel pressure drops gradually
after engine is stopped
Leaky injector
Replace injector
Leaky fuel regulator valve seat
Replace fuel pressure regulator
Fuel pressure drops sharply
immediately after engine is
stopped
Check valve in fuel pump is held
open
Replace fuel pump
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