Fuel System Air Leak Vacuum Test

The proceeding test will determine if a fuel system air leak exists at the engine. Air leaks will cause hard starting and/or poor performance.

Fig.2 Hand-Operated Vacuum Pump (Typical):

A hand-operated vacuum pump/gauge equipped with a remote or built-on fluid container will be used. A typical hand-operated pump is shown in (Fig. 2). The use of a hand-operated pump with a fluid container will prevent fuel oil from entering and possibly damaging pump. Two rubber caps (one 5/16" and one 3/8") will also be used to temporarily plug / seal fuel system.

Vacuum Test Set-Up, Specifications and Conditions
Examine all engine fuel system components, fittings, lines and hoses for visual evidence of fuel leakage. Repair as necessary before proceeding.

Be sure gauge on your hand-operated pump is accurate and pump does not leak. Perform a simple test on pump. Add a 3 foot section (minimum) of clear plastic hose to the pump.

Apply maximum 15-20 inches of vacuum for tests.
System should hold 15-20 inches of vacuum for 5 continuous minutes. After 5 minutes, vacuum should not drop more than 0.1 inch Hg for 1 minute.

Fig.3 Quick-Connect Fittings Location:

Disconnect fuel supply and return lines (quick connects) at rear of engine (Fig. 3).

Drain as much fuel as possible from engine fuel lines. Also, completely drain fuel filter/water separator housing. Refer to Fuel Filter/Water Separator Removal and Installation for fuel draining procedures. This step must be done to prevent liquid fuel from entering and possibly damaging your hand-operated pump.

Testing All Engine Fuel System Components Together
This test will indicate an air leak is present somewhere on the engine.
1. Be sure water drain valve is securely closed.
2. Examine all engine fuel system components, fittings, lines and hoses for visual evidence of fuel leakage. Repair as necessary

Fig.4 Vacuum Pump Installed To Fuel Line:

3. Install 5/16" rubber cap to fuel return line on engine (Fig. 4).
4. Install hand-operated vacuum pump to fuel supply line on engine (Fig. 4).
5. Perform vacuum test. Be careful not to allow liquid fuel to get into your hand-operated vacuum pump.
6. Vacuum holds ? End of test; no leaks found on engine.
7. Vacuum leak ? Proceed. The following tests will isolate the component that is leaking.

Testing Fuel Transfer Pump

Fig.5 Fuel Hose At Transfer Pump:

1. Leave vacuum pump attached to fuel supply line (Fig. 5).
2. Disconnect rubber fuel hose from fitting at outlet side of fuel transfer pump (Fig. 5). To plug I seal system, install 3/8" rubber cap to this fitting (Fig. 5).
3. Perform vacuum test. Be careful not to allow liquid fuel to get into your hand-operated vacuum pump.
4. Vacuum leak ? Check/repair all transfer pump fittings and sealing washers for leaks. Check/repair rubber hose and clamps at sides of transfer pump for leaks. Perform another vacuum test. If leak still present, replace fuel transfer pump.
5. Vacuum holds ? Proceed.

Testing Fuel Filter / Water Separator
1. Leave vacuum pump attached to fuel supply line (Fig. 4).

Fig.6 Fuel Hose At Fuel Filter:

Fig.7 Capping Off Fuel Filter Outlet Line:

2. Disconnect rubber fuel hose located between VP-44 pump and fuel filter/water separator (Fig. 6). To allow easier hose removal, remove test port fitting and fuel inlet line at VP-44 pump (Fig. 6). To plug / seal system, install 3/8" rubber cap to this outline line (Fig. 7).
3. Reconnect rubber fuel hose to fitting at outlet side of fuel transfer pump (Fig. 5).
4. Perform vacuum test. Be careful not to allow liquid fuel to get into hand-operated vacuum pump.
5. Vacuum leak ? Check/repair all fittings and sealing washers for leaks. Check/repair rubber hose and clamps for leaks. Check fuel heater and water-in-fuel sensor O-rings for leaks. Check filter canister seal at top of canister for leaks. Repair as necessary
6. Vacuum holds ? Proceed.

Testing VP-44 Pump and Fuel Return I Drain System Within Cylinder Head
1. Leave vacuum pump attached to fuel supply line (Fig. 4).
2. Position rubber hose and 2 clamps to VP-44 drain line. Install test port fitting and fuel drain line to VP-44 pump. Tighten test port fitting to 24 Nm (18 ft. lbs. or 212 in. lbs.) torque. Position 2 hose clamps to rubber hose.

Fig.8 T Fitting - Top Disconnected:

3. Loosen, but do not remove, fuel line support bracket bolt (Fig. 8).
4. Disconnect and separate fuel drain line at top of "T" fitting (Fig. 8). To plug / seal system, install 3/8" rubber cap to this disconnected line (Fig. 8).
5. Perform vacuum test. Be careful not to allow liquid fuel to get into your hand-operated vacuum pump.
6. Vacuum leak ?
a. Check return line banjo bolt and sealing washers at rear of cylinder head for leaks. Repair as necessary
b. Remove all high-pressure fuel lines at injector high-pressure connectors. Examine all injector connector O-rings. If any damage to O-ring exists, replace connector.
c. If no damage is found at connectors, remove all 6 fuel injectors to inspect O-rings and sealing washers. Also inspect cylinder head bores where these sealing washers make contact. The bore contact area should be smooth and uniform.

7. Vacuum holds ? Proceed.

Testing VP-44 Pump and its Return Line
1. Remove rubber 3/8" sealing cap and reconnect I tighten fuel drain line to top of "T" fitting (Fig. 8).

Fig.9 T Fitting - Front Disconnected:

2. Disconnect and separate VP-44 drain line at front of "T" fitting (Fig. 9). To plug I seal system, install 3/8" rubber cap to this disconnected line (Fig. 9).

Fig.10 Vacuum Pump At VP-44 Pump:

3. Disconnect rubber fuel hose at VP-44 inlet (Fig. 10). Connect your hand-operated vacuum pump at this inlet point.
4. Perform vacuum test. Be careful not to allow liquid fuel to get into your hand-operated vacuum pump.
5. Vacuum leak ? Check condition of banjo fittings, banjo bolts, and sealing washers. If leaks are not present, a leak exists within VP-44 pump. Replacement of VP-44 requires authorization.