Assembly
For flexibility and ease of storage, the FST Pro features a modular
design that is quick to assemble and breakdown. Proper assembly
for testing is covered in the Setup and Installation instructions
Bypass Hose
Prior to the first use of the FST, the 1/4" (6.5 mm) ID clear bypass hose
should be assembled to the bypass port extending from the side of the
flowmeter, above the flow control valve. To connect the fuel bypass
hose:
1. Unscrew the compression nut from the fuel bypass port extend-
ing from the side of the flowmeter just above the flow control valve
(Fig. 1).
2. Slip the compression nut over one end of the clear bypass hose,
1/4" (6.5 mm) ID x 6’ (1.8 m) long (Fig. 2).
3. Push the end of the bypass hose over the barb extending from the
bypass port (Fig. 3).
4. Slide the compression nut up over the end of the tube and
thread it back onto the bypass port. Tighten the nut using a
7/16" open-end wrench (Fig. 4).
Proper Use, Care and Servicing
With proper care and maintenance, the FST Pro will provide years of
accurate, reliable service.
The FST is designed for use in testing modern fuel delivery systems
on vehicles equipped with gasoline or diesel powered combustion
engines.
• Always drain the fuel from the FST prior to storage.
• Always disassemble the FST and return it to the storage case in
which it was originally purchased.
• Inspect components regularly for damage and replace or repair as
necessary:
- Check hoses for cracks and cuts
- Check adapters for damage and wear to threads and
sealing surfaces
- Check female quick-connects for wear and cuts to o-rings
- Inspect the male and female quick-connect components
where the pressure gauge connects to the flowmeter
•
After installing the FST and pressurizing the fuel system, check the
flowmeter for leaks. If any leaks are evident, immediately relieve
the pressure, disconnect the FST, and return it for repair.
Page Number - 16
Form 824262
Faulty Fuel Pressure Regulator (Low Pressure)
A pressure regulator that does not sufficiently restrict fuel flow will
cause the idle pressure in Zones 1 and 2 to drop below spec, and the
idle flow to be higher than normal. If this is what the FST is indicating,
and the peak pressure and flow are normal, then the cause is most
certainly the pressure regulator.
If the fuel pressure regulator is vacuum modulated (see
Fuel System
Components/Pressure Regulator
), it is possible to check if it is
sticking by disconnecting the vacuum line. If the regulator is
functioning properly, disconnecting the vacuum line should
cause the fuel pressure to increase.
Faulty Fuel Pressure Regulator (High Pressure)
If Zone 2 testing indicates idle pressure is high and flow is low, yet
peak pressure and flow are normal, this is a clear indication of too
much restriction in Zone 3. Over-restriction can be caused by a mal-
functioning fuel pressure regulator or blockage in the return fuel line.
Perform a careful visual inspection of the fuel return line to ensure it’s
not crushed, dented or kinked. Plastic and rubber fuel lines can easily
kink, restricting fuel flow. Check for clamps that might have been over
tightened to the point they crushed the fuel line. Also check all
connectors for damage that could cause a restriction. If damage or
restriction is noted, repair the line and retest.
Inspect the fuel pressure regulator for physical damage. Also look for
dampness that could indicate a ruptured diaphragm that is leaking fuel.
Replace and retest if necessary.
If the pressure regulator is vacuum modulated, use a vacuum gauge
to verify the vacuum reading at the regulator. A below normal vacuum
reading would cause the regulator to over-restrict the flow. Follow the
vehicle manufacturer’s procedure for locating and repairing the cause
of the vacuum loss, and retest.
If vacuum is normal, connect the FST in Zone 3, preferably right after
the pressure regulator. Test the fuel system at this point, and compare
the results to Zone 2. The pressure in Zone 3 should be very low. If it
remains high, there is a restriction in the fuel return line. If the pressure
drops off to near zero, then replace the fuel pressure regulator.
Fuel Pump Malfunction
A malfunction at the fuel pump is typically indicated by a reduction in
both pressure and flow. At idle, the regulator may be able to maintain
pressure in Zones 1 and 2, but doing so will severely reduce the flow.
Performing pressure and flow demand tests should clearly indicate a
pump problem.
If the FST indicates a pump is under performing, be sure to verify that
the vehicle does not use a multiple speed pump (see
Fuel System
Components/Fuel Pump
). To properly test a fuel system with a
multiple speed pump, a scanner must be used to operate the pump
at high speed while the vehicle idles.
NOTE:
Insufficient pressure and flow are an indication that a fuel pump
is under-performing, but do not necessarily mean that it is
failing. Low voltage or a bad connection or ground will cause a
pump to under-perform, producing the same test results as if the pump
were bad. Before replacing any fuel pump based on the FST test
results, always follow the vehicle manufacturer’s recommended
procedure for testing all electrical connections and the electrical
system charge. A minor issue such as a loose ground can cause many
problems that resemble more serious malfunctions.
Fig. 23
Fig. 22
Fig. 24
