Fuel Pressure: Testing and Inspection
1. Release residual pressure from the fuel line to prevent fuel spray.
2. Disconnect the high-pressure fuel hose at the fuel rail side.
CAUTION: Cover the hose connection with shop towel to prevent splash of fuel that could be caused by some residual pressure in the fuel pipe line.
3. Remove the union joint and bolt from the special tool (adapter hose MD998709) and instead attach the special tool (hose adapter MD998742) to the adapter hose.
4. Install a fuel pressure gauge on the adapter hose that was set up in step 3.
- Use a suitable O-ring or gasket between the fuel pressure gauge and the special tool so as to seal in order to prevent fuel leakage at this time.
5. Install the special tool, which was assembled in steps 3 and 4 between the fuel rail and the high pressure hose.
6. Use the scan tool "Fuel System Test" to drive the fuel pump. Check no fuel leakage in the fuel pressure gauge connection and the special tool connection.
7. Start the engine and run at idle.
8. Measure fuel pressure while the engine is running at idle.
Standard value:
- Approx. 265 kPa (38 psi) at curb idle
9. Disconnect the vacuum hose from the fuel pressure regulator. Measure fuel pressure with the hose end closed by a finger.
Standard value: 324 - 343 kPa (47 - 50 psi) at curb idle
10. Race the engine several times. Check that fuel pressure at idle does not drop.
11. Racing the engine repeatedly, hold the fuel return hose lightly with 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 pressure in the return hose.
12. If any of the fuel pressure measured in steps 8 to 11 is out of specification, troubleshoot and repair according to the table below.
Symptom Fuel pressure too low or No fuel pressure in fuel return hose
Probable Cause Followed by Recommended Action
- 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
Symptom Fuel pressure too high
Probable Cause Followed by Recommended Action
- Binding valve in fuel pressure regulator -- Replace fuel pressure regulator
- Clogged fuel return hose or pipe -- Clean or replace hose or pipe
Symptom No change in fuel pressure with/without vacuum hose connected
Probable Cause Followed by Recommended Action
- Damaged vacuum line or clogged nipple -- Replace hose or clean nipple.
13. Stop the engine and observe fuel pressure gauge reading. Normal if the reading does not drop within 2 minutes.
- If it does, observe the rate of drop. Troubleshoot and repair according to the table below.
Symptom Fuel pressure drops gradually after engine is stopped
Probable Cause Followed by Recommended Action
- Leaky injector -- Replace injector
- Leaky fuel regulator valve seat -- Replace fuel pressure regulator
Symptom Fuel pressure drops sharply immediately after engine is stopped
Probable Cause Followed by Recommended Action
- Check valve in fuel pump is held open -- Replace fuel pump
14. Release residual pressure from the fuel pipe line.
15. Remove the fuel pressure gauge and special tool from the fuel rail.
CAUTION: Cover the hose connection with shop towel to prevent splash of fuel that could be caused by some residual pressure in the fuel pipe line.
16. Replace the O-ring at the end of the high-pressure fuel hose.
17. If the high-pressure fuel hose into the fuel rail and tighten the bolts to specified torque.
- Tightening torque: 5 Nm (3.6 ft lb)
18. Check for fuel leaks.
a. Use the scan tool "Fuel System Test" to drive the fuel pump.
b. Check the fuel line for leaks. Repair if necessary.