Fuel Pressure Test

Reduce the internal pressure of the fuel lines and hoses:
- Disconnect the fuel pump harness connector
- Start the engine and after it stalls, turn the ignition switch to the OFF position
- Disconnect the battery negative (-) terminal
- Connect the fuel pump harness connector
Fig 1: Disconnecting Fuel Pump Electrical Connector
Courtesy of HYUNDAI MOTOR CO.
Remove the bolt connecting the fuel line to the fuel delivery pipe.

Fig 2: Removing Fuel Line From Fuel Delivery Pipe
Courtesy of HYUNDAI MOTOR CO.

CAUTION: Cover the hose connection with a shop towel to prevent splashing of fuel caused by residual pressure in the fuel line.
Using the fuel pressure gauge adapter, install the fuel pressure gauge to the fuel pressure gauge adaptor. Tighten the bolt to the specified torque.
Fuel pressure gauge to fuel delivery pipe:

25~35 Nm (250~350 kg.cm, 18~26 lb.ft)

Fig 3: Installing Fuel Pressure Gauge
Courtesy of HYUNDAI MOTOR CO.
Connect the battery's negative (-) terminal.
Apply battery voltage to the terminal for the pump drive and activate the fuel pump. With fuel pressure applied, check that there is no fuel leakage from the pressure gauge or connection part.
Start and run the engine at curb idle speed.
Disconnect the vacuum hose from the pressure regulator, and plug the hose end. Measure the fuel pressure at idle.
Standard value:

320~340 kPa (3.26~3.47 kg/cm² , 46~49 psi)

Fig 4: Disconnecting & Plugging Fuel Pressure Regulator Vacuum Hose
Courtesy of HYUNDAI MOTOR CO.
Measure the fuel pressure when the vacuum hose is connected to the pressure regulator.
Standard value:

Approx. 255 kPa (2.57 kg/cm² , 37 psi)

If the results of the measurements made in steps (7) and (8) are not within the standard value, use the table below to determine the probable cause, and make the necessary repairs.

PROBLEM SYMPTOM TABLE - FUEL PRESSURE (ENGINE RUNNING)

Condition	Probable cause	Remedy
Fuel pressure is too low	Clogged fuel filter Fuel leakage to the return side, caused by poor seating of the fuel-pressure regulator	Replace fuel filter Replace fuel pressure regulator
Fuel pressure is too low	Low discharge pressure of the fuel pump	Check the in-tank fuel hose for large or replace the fuel pump
Fuel pressure is too high	Sticking fuel pressure regulator Clogged or bent fuel return hose or pipe	Replace fuel pressure regulator Repair or replace hose or pipe
There is no difference in fuel pressure when the vacuum hose is connected and when it is not.	Clogged, or damaged vacuum hose or nipple Sticking or poor seating of the fuel pressure regulator	Repair or replace the vacuum hose or the nipple Repair or replace hose or pipe

Stop the engine and check for a change in the fuel pressure gauge reading, which should hold for approximately 5 minutes. If the gauge indication drops, observe the rate at which it drops. Determine and remove the causes according to the following table.

PROBLEM SYMPTOM TABLE - FUEL PRESSURE (AFTER ENGINE IS SHUT OFF)

Condition	Probable cause	Remedy
Fuel pressure drops slowly after engine is stopped	Injector leakage	Replace injector
Fuel pressure drops immediately after engine is stopped	The check valve within the fuel pump is open	Replace fuel pump

Reduce the pressure in the fuel line.
Disconnect the hose and the gauge.
CAUTION: Cover the hose connection with a shop towel to prevent splashing of fuel caused by fuel residual pressure in the fuel line.
Replace the O-ring at the end of the hose.
Connect the fuel hose to the delivery pipe and tighten to the specified torque.
Check for fuel leakage.
- Apply battery voltage to the fuel pump drive terminal to operate the fuel pump.
- With pressure, check the fuel line for leaks.
Fig 5: Applying Battery Voltage To Fuel Pump Connector
Courtesy of HYUNDAI MOTOR CO.