Mityvac MV5545 User Manual download pdf (Page 13)

Fig. 20

Form 824127 Page Number - 13

When the valve is rotated to the BYPASS position pointing up, fuel is

routed through the bypass port located on the side of the flowmeter

just above the flow control valve (Fig. 20). Bypassing eliminates all

restriction to the flow, and the maximum volume output of the pump

is indicated on the flowmeter. Fuel pressure will drop to zero. This is

ermed the Peak Flow Test, and is applicable to return and returnless

systems.

If the flow control valve in the CLOSED position is considered to

simulate a closed throttle, and the BYPASS position is considered

to simulate wide-open throttle (WOT), then any position in-between

would represent some unique throttle position between idle and WOT.

With this in mind, the operator can simulate any engine demand

scenario by simply rotating the valve between CLOSED and BYPASS.

By monitoring the corresponding pressure and flow on the FST, the

fuel delivery system’s ultimate capability to meet engine requirements

can be determined.

Although it may sound complicated, applying this principle is quite

simple. For example a 3.8L engine with a maximum speed of 6,000

rpm can require an estimated flow of up to .34 GPM (1.3 LPM) of fuel

(see Appendix A). Keeping an eye on the flowmeter, the valve should

be rotated from the OPEN position, past the CLOSED position until

the reading across the top of the float is .34 GPM. The corresponding

pressure value should be noted. On a return system or electronically

regulated returnless system, the pressure value should be higher than

the manufacturer’s specification. On a mechanically regulated returnless

system, the pressure should be within the manufacturer’s specification.

Pinpointing Fuel System Malfunctions

To pinpoint the cause of a fuel system malfunction, a simple

knowledge of fuel system components, and their affect on system

performance, is combined with the results from the tests above to

determine the most likely point of failure. For example, initial FST

testing of a return fuel system would yield values for four critical

performance indicators, Idle Pressure, Idle Flow, Peak Pressure, and

Peak Flow. A clogged inline fuel filter would restrict fuel flow, causing

low values for idle and peak flow, but idle and peak pressure would

remain within spec. An under-restricting pressure regulator would

produce a higher than normal idle flow and low idle pressure, but

normal values for peak flow and peak pressure. Noting the values

of these test indicators, and comparing them to the vehicle’s

specifications, the technician can in most cases accurately pinpoint

the cause of a malfunction.

Testing a returnless system will generate performance measurements

for Idle Pressure, Peak Flow, and Peak Demand Pressure. The values

for these indicators are applied in the same way, to pinpoint the cause

of a fuel system malfunction.

This logic can be applied to all components that can influence fuel

delivery system performance. The details of this method are

documented in the Testing and Diagnostic section of this manual.

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 41 42

Comments to this Manuals

No comments

Mityvac MV5545 User Manual Page 13

Comments to this Manuals