Kia Optima: Fuel Pressure Test - Repair procedures - Fuel Delivery System - Engine Control/Fuel System - Kia Optima TF 2011-2020 Service ManualKia Optima: Fuel Pressure Test

1. Release the residual pressure in fuel line (Refer to Release Residual Pressure in Fuel Line in this group).
When removing the fuel pump relay, a Diagnostic Trouble Code (DTC) may occur. Delete the code with the GDS after completion of Release Residual Pressure in Fuel Line work.
2. Install the Special Service Tool (SST).
(1) Disconnect the fuel feed tube from the high pressure fuel pump.
There may be some residual pressure even after Release Residual Pressure in Fuel Line work, so cover the hose connection with a shop towel to prevent residual fuel from spilling out before disconnecting any fuel connection.
(2) Install the special service tool for measuring the fuel pressure in between the fuel feed tube and the high pressure fuel pump (Refer to the figure below).

3. Inspect fuel leakage on connections among the fuel feed tube, the high pressure fuel pump, and the SST components with IG ON.
4. Measure Fuel Pressure.
(1) Start the engine and measure the fuel pressure at idle.

Fuel Pressure: 495 ~ 505 kPa (5.1 ~ 5.2 kgf/cm², 71.8 ~ 73.2 psi)
If the fuel pressure differs from the standard value, repair or replace the related part (Refer to the table below).

Fuel
Pressure
Cause
Related Part
Too Low
Fuel filter clogged
Fuel Filter
Fuel leakage
Fuel Pressure Regulator
Too High
Fuel pressure regulator stuck
Fuel Pressure Regulator

(2) Stop the engine, and then check for the change in the fuel pressure gauge reading.

Standard Value: The gauge reading should hold for about 5 minutes after the engine stops
If the gauge reading should not be held, repair or replace the related part (Refer to the table below).

Fuel Pressure
(After Engine Stops)
Cause
Related
Part
Fuel Pressure Drops Slowly
Leakage on injector
Injector
Fuel Pressure Drops Immediately
Check valve of fuel pump stuck open
Fuel Pump

(3) Turn the ignition switch OFF.
5. Release the residual pressure in fuel line (Refer to Release Residual Pressure in Fuel Line).
When removing the fuel pump relay, a Diagnostic Trouble Code (DTC) may occur. Delete the code with the GDS after completion of Release Residual Pressure in Fuel Line work.
6. Test End
(1) Remove the Special Service Tool (SST) from the fuel feed tube and the high pressure fuel pump.
(2) Connect the fuel feed tube and the high pressure fuel pump.

Repair procedures
...

Release Residual Pressure in Fuel Line
Whenever the high pressure fuel pump, fuel pipe, delivery pipe, or injector is removed immediately after shutting off the engine, an ...

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