WS4 Fuel Pressure and flow

WS4 Fuel Pressure and flow (Petrol only)


Warning, be careful around raw fuel. It can catch fire! Use appropriate safety precautions. Keep sparks, flame, your body and your clothing away from raw fuel! Know where your fire extinguishers are and use them if necessary.


1. Locate the two closest fire extinguishers. (If you have to use it remember to pull the pin, squeeze the handle, and spray at the base of the flame.) Write down where they are:
               Fire extinguishers are located by the main door.


2. If you can, look up Fuel Pressure specifications for the vehicle you are testing. If you can’t look them up, make a guess at the fuel specs you should have and write them down here:
              265 ~ 304 kPa (2.7 ~ 3.1 kgf/㎠, 38 ~ 44 psi) 
3. Use eye protection. Optional: Relieve fuel pressure before installing pressure gauge. Or there will be some fuel that sprays at you as you attach the gauge. You can relieve pressure by several methods: 1) To relieve the fuel pressure. Make sure you have a rag to catch the fuel, start the engine. 2) Remove fuel pump (circuit opening) relay or fuse and run the engine until it stops, then crank to check that the engine doesn’t start 3) Use a vacuum gauge on the pressure regulator to lower fuel pressure, or 4) Open a fuel line at some pressure point and catch the fuel in a rag beware there may be lots of fuel.

4. Attach fuel pressure gauge and notice which scale on the gauge you will be using. Briefly turn key on or start vehicle, then turn it off. Check for fuel leaks.
Are there leaks? Yes ..................... No .....√.......
If there are leaks you must correct them and retest before continuing. If you need help, ask ! 

5. Measure the fuel pressure with the key on, engine off.
Record it here: 300 kPa (also record the units you are using, psi, bar,
Kpa, etc…) 43 psi 

6. Idling: Measure the fuel pressure with the engine idling. Watch the pressure for a couple of minutes.
Record pressure here: 280 kPa

7. Maximum: With the engine idling, use the special tool to clamp the fuel return line. Note: this can only be done for a short period.                                                      
Record pressure here: 600 kPa      

8. WOT: With the engine idling, disconnect and plug the vacuum line going to the fuel pressure regulator.
Record pressure here: 340 kPa        
9. Residual: Turn off the engine, and watch the fuel pressure for five minutes.
Record your residual or rest pressure here: 300 kPa      
10. Flow: Hook up proper equipment to read fuel volume if necessary. Record flow gauge results of volume, or how much pumped in 15 seconds: (normal results may be ½ liter in 15 seconds) 
                                      Around 900 ml 

11. Replace vacuum lines. Carefully remove the fuel pressure gauge (beware of fuel spraying into eyes, avoid sparks, etc.) Turn engine key on and off, check for leaks. Start engine, check for leaks. No leaks? Check here:
Replace cap over fuel pressure test port. Check when done: OK 
Make sure the vehicle is safe and runs fine when done, or tell your instructor.

12. Explain why it is important to know a vehicle fuel pressure/flow?
 The injector operates correctly under the correct fuel pressure.

13. Describe the symptoms a vehicle would give with each case

Low fuel pressure
 The engine idling drops and the engine runs roughly. The engine performance reduces significantly. 
Low fuel flow
 Low fuel flow is occured by blocked fuel filter and weak reaturn valv and fuel pump. This produces low fuel pressure  and rough idling as well due to insufficent fuel suppling for injectors.

High fuel pressure High fuel pressure is produced by the fault of the return fuel regulator. More fuel goes through the injectors with dripping fuel to the injectors. 

Faulty fuel pressure regulator
 Flouding of injectors with high fuel pressure which will leak out the injectors. This causes hard starting, poor econmic and the high consumptin of fuel.