Mityvac MV5545 User Manual download pdf (Page 22)

Fig. 40

Fig. 39

Fig. 41

Read top

of float

Page Number - 22 Form 824127

Testing and Diagnostics

Testing and diagnostic procedures vary depending on the type of fuel

delivery system. Prior to testing, the fuel delivery system must be

identified as Return, Returnless (mechanically regulated) or Returnless

(electronically regulated). For detailed information on fuel delivery sys-

ems and how to identify them, refer to the section entitled Types of

Fuel Delivery Systems, earlier in this manual. If the fuel system is a

return or mechanically regulated returnless system, it must also be

determined if the fuel pump has multiple speeds. For more informa-

tion on types of fuel pumps refer to Fuel System Components/Fuel

Pump in this manual.

Return Fuel Delivery Systems

At this point, it is assumed that the FST has been properly installed

inline with the fuel delivery system as recommended, and that it has

been primed to ensure no leaks are present (see Setup and

Installation). The following procedure will ensure the most effective

diagnostic use of the FST:

Test Procedure

Operational Test

1. Check the operating position of the flow control valve on the side

of the flowmeter to ensure the knob is in the OPEN position point-

ing down (Fig. 39). This will allow normal fuel system operation.

2. Start the car and allow it to idle.

Cranking or starting the engine should activate the ECM’s electric

fuel pump controls to turn on and run the fuel pump. If the fuel

pump does not operate, refer to the vehicle service information for

electrical diagnosis and repair of the fuel pump and associated

controls.

After connecting the FST, it is normal to have air trapped in the

fuel lines and flowmeter. Cycling the ignition switch (or cranking

the engine briefly) with the flow control valve in the BYPASS posi-

tion can help purge air from the system. Once fuel fills the

flowmeter and flows through the bypass hose, return the valve to

the OPEN position. The bypass hose must be routed and secured

into an approved fuel container before operating the flow control

valve in BYPASS mode.

To perform an accurate diagnosis using the FST, the car must be

running in order to provide the correct operating voltage to the

fuel pump. Testing the fuel system by activating the fuel pump

using a scan tool will cause the fuel pump to severely under-per-

form.

3. If the vehicle utilizes a multiple speed fuel pump, use a scanner or

manufacturer’s recommended procedure to operate the pump at

the highest speed.

4. Note the fuel system pressure indicated on the pressure gauge,

and compare it with the vehicle manufacturer’s specification (Fig.

40).

Typical electronic fuel injection system pressures range from 30 to

60 PSI (205 to 410 kpa) depending on the vehicle being tested.

Always use the recommended vehicle service information, proce-

dures, and pressure specifications for the specific vehicle being

tested.

5. Note the volume of fuel passing through the flowmeter by reading

across the top of the float and comparing it to the corresponding

value on the scale printed on the faceplate (Fig. 41).

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Mityvac MV5545 User Manual Page 22

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