WS4 - Fuel Pressure and Flow ( Petrol only )

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

1. Locate the two closest fire extinguishers.

2. Look up fuel pressure specifications for the vehicle you are testing.

Toyota 4A-FE engine, the fuel pressure specification is 265-304KPa.

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 does not 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? If there are leaks you must correct them and retest before continuing. If you need help, ask !  

There is no fuel leaks.

5. Measure the fuel pressure with the key on, engine off.  

Record it here:  300kpa / 43psi

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

Record pressure here:  272kpa

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: Over 600kpa

 

8. WOT: With the engine idling, disconnect and plug the vacuum line going to the fuel pressure regulator.  

Record pressure here:  338kpa

9. Residual: Turn off the engine, and watch the fuel pressure for five minutes.  

Record your residual or rest pressure here:  300kpa

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)  

Can not be done here.

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:  

Make sure the vehicle is safe and runs fine when done, or tell your instructor. 

Can not be done here.

Description:

The fuel pressure is important because ECU control the EFI by PWM. higher pressure means more fuel sprayed in the same period of time, and lower pressure will spray less fuel.

If the fuel pressure or the fuel flow is low. There is less fuel will be sprayed than the ECU wants, so that makes the mixture go lean. The vehicle will lack of power, less performance, rough idling.
If the fuel pressure is high or the fuel pressure regulator is faulty and create high pressure in the pipe, more fuel will be sprayed than the ECU wants and mixture goes rich. The fuel economy is bad and black smoke come out off tail pipe, rough idling, bad emission.