Mityvac MV5545 User Manual download pdf (Page 26)

Fig. 46

Fig. 45

Fig. 47

Page Number - 26 Form 824127

Returnless Fuel Delivery Systems

(Mechanically Regulated)

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 FST Pro 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. 45). 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.

46). If it is out of spec, this is an indication of a problem with one

or more components of the fuel system. However, performing a

Flow Demand Test and Capability Test as outlined below, are

required to reach an accurate diagnosis of the fuel system, and to

pinpoint the cause of the malfunction.

NOTE: The flow of fuel passing through the tester represents only

what the engine is using at idle. It will be negligible and most likely

not even register on the flowmeter.

Flow Demand Test

5. With the car idling, rotate the flow control valve past the CLOSED

position to the BYPASS position pointing up (Fig. 47).

With the valve in the BYPASS position, the flow of fuel is routed

through the bypass port located above the valve, through the

bypass hose, and into the reservoir. All restriction to the flow of

fuel is removed. This allows the pump to output its maximum flow,

the value of which can be read on the flowmeter. The free flow

output of a typical fuel pump is between .7 and 1.0 GPM (2.5 and

4 LPM).

NOTE: Turning the valve to the CLOSED or BYPASS position will

prevent fuel from flowing to the engine. If left in either of these

positions for too long, the engine will stall. If this happens, simply

return the valve to the OPEN position and restart the vehicle.

6. After noting the peak flow, return the flow control valve to the

1 2 ... 21 22 23 24 25 26 27 28 29 30 31 ... 41 42

Comments to this Manuals

No comments

Mityvac MV5545 User Manual Page 26

Comments to this Manuals