Mityvac MV5545 User Manual download pdf (Page 32)

Fig. 56

Fig. 57

Page Number - 32 Form 824127

5. Turn off the engine and immediately clamp off the FST inlet hose

unning to the tester from the fuel supply line. This will trap the

pressure gauge between the clamp, the fuel rail, the pressure reg-

ulator, and the fuel return line.

6. If the pressure drops, either the injectors or the pressure regulator

is leaking.

7. With the second scissor clamp, pinch off the fuel return line

between the pressure regulator and the fuel tank.

. If the pressure continues to drop, the cause is a leaking injector(s).

If the pressure holds steady, the cause is a leaking pressure regu-

lator.

Returnless Fuel Systems

1. Start the engine to build pressure.

2. Turn off the engine and immediately clamp off the FST outlet hose

running from the tester to the fuel rail. This will trap the pressure

gauge between the clamp and the fuel pump module.

3. If the pressure gauge indicates a leak, check the fuel supply line

from the tank to the tester. If no leaks are evident, replace the fuel

pump module due to a faulty pump check valve or leaking regula-

tor.

4. Remove the clamp from the fuel line, and restart the engine to

build pressure.

5. Turn off the engine and immediately clamp off the FST inlet hose

running to the tester from the fuel supply line. This will trap the

pressure gauge between the clamp and the fuel rail.

6. If the pressure drops, the cause is a leaking injector(s).

Disconnecting the FST

The FST Pro contains features and components to safely disconnect

with a minimal release of fuel. Follow the procedures below and

always observe the safety precautions listed in the front of this manu-

al. Carefully read the warning below concerning disconnecting from a

hot returnless fuel system.

1. When vehicle testing is completed, turn off engine and relieve

pressure on the fuel system by pressing the pressure relief valve

located on the stem of the pressure gauge (Fig. 56). Watch the

pressure gauge readings and fuel being released through the

small clear hose to the collecting container.

2. The flow control valve must remain in the OPEN position during

pressure relief. When fuel pressure is not shown on the gauge,

and fuel stops flowing through the relief hose, proceed to step 3.

3. Place shop towels under the connections to capture any fuel that

may spill out when the hoses are disconnected.

4. Using the two scissor hose clamps supplied in the FST Pro kit,

clamp both of the connecting hoses near the end where they con-

nect to the vehicles fuel system (Fig. 57). Lock them securely to

prevent fuel from leaking out of the tester when the hoses are dis-

connected.

WARNING: After testing a returnless fuel system, use extreme

caution when disconnecting the outlet hose connecting the FST

to the fuel rail. If the engine is hot, releasing the pressure from a

returnless fuel system will cause the fuel to boil in the fuel rail.

Even though the pressure has been released, the boiling fuel will

cause it to build up again once the hose is clamped. To reduce

the risk of fuel spray it is best to allow the engine to cool before

disconnecting the hose. Otherwise, use the FST pressure relief

valve to relieve the pressure just before clamping the hose. Once

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Mityvac MV5545 User Manual Page 32

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