WS4

WS4Fuel Pressure and flow (Petrol only)

Make Toyota Model 4A-FE Year 1998

Locate the two closest fire extinguishers. 

 For safety to avoid rick while working on high fuel pressure during this task, we well aware the dangerous of fuel and therefore we need to be able to locate the nearest fire extinguishers in case of an emergency.The warning sign show some tip for safety percussion.

SAFETY TIPS:

Pressure specifications

                                                                                        A Type (36 PSI)          B Type (41 PSI)   

Test Condition	Min	Max	Min	Max
Engine Cranking	33 psi	40 psi	38 psi	46 psi
Engine Running (Regulator hose Connected)	23 psi	30 psi	33 psi	37 psi
Engine Running (Regulator disconnected)	33 psi	40 psi	38 psi	46psi
Engine Off Residual Pressure (after 5 min)	21 psi		21 psi
Maximum Pump Pressure/pressure relief point
Minimum Delivery Volume (after 30 sec)	1 litre		1 litre

Attach fuel pressure gauge and recorded scale on the gauge. than we turn the key on and start vehicle, then turn it off. We check for sign of any possible leak and we note it was good. 

 The fuel pressure showing with the key on, engine off.

Record it here: 44psi

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

Record pressure here 40psi

Maximum: With the engine idling, we use the special tool to clamp the fuel return line.

Note: this can only be done for a short period.

Record pressure here 85psi

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

Record pressure here 49psi

Residual: We turn off the engine, and watch the fuel pressure for five minutes.

Record your residual or rest pressure here: 38psi – 44psi

Importance of knowing vehicle fuel pressure/flow?

We check how it perform, and most importantly to determine ensure if pressure rises above to its minimum specification. Fail performance due to fault test in fuel pressure could result of an explosion when there is fuel leaking makes contact with heat temperature in the area or electrical sparks from the engine.  

Low fuel pressure

Low intake manifold pressure or Idle for example pulls on the diaphragm decreasing spring pressure. This allows more fuel to return to the fuel tank decreasing pressure in the fuel rail.

When the engine is idling, or under normal driving conditions. When a small amount of fuel is required, the pump control relay.

Low fuel flow

After the engine starts, during idle and light loads, the ECU outputs a low signal (2.51volts) to the fuel pump ECU. Then, the fuel pump ECU supplies less voltage (8.9volts) to the fuel pump cause low fuel flow.

High fuel pressure

When the engine crank, or operating under a heavy load at high RPM or starting, the ECU sends a 5v signal to the fuel pump ECU. The fuel pump ECU then applies battery power to the fuel pump causing the fuel pump to operate at high speed.

Faulty fuel pressure regulator

Fault regulator would affect the maintaining constant pressure differential across the fuel line and shorten the injector cause misfire.