Merc 175, air in fuel system

[dwm0121]

I just replaced my fuel filter water separator. I didn't fill it with fuel when I put it back on. Now I have air in the system. I bled it to the point where the fuel line connects to the front of the engine. Still won't fire. Do I need to do anything on the engine, or will it work its way out if I keep cranking the engine?

 

[CharlieB]

Re: Merc 175, air in fuel system

The primer bulb 'should' work to prime the filter and push all the air out and fill the carbs. If the primer is not working try holding it straight up so the tank hose is bottom and the hose to the motor is on top, this allows gravity to assist seating the check ball valves to seal.

Aftermarket primer bulbs often have only one check valve, Merc primers have a check valve on BOTH inlet and outlet. Many mechanices will only install a Merc primer.

Once the primer is firm and the motor still does not start then start checking for spark on each cyl.

 

[dwm0121]

Re: Merc 175, air in fuel system

It is injected, not sure if that makes a difference. Ball is hard, started this morning first crank, shouldn't be a spark issue. Anything else it could be?

 

[dwm0121]

Re: Merc 175, air in fuel system

It is injected, not sure if that makes a difference. Ball is hard, started this morning first crank, shouldn't be a spark issue. Anything else it could be?

 

[CharlieB]

Re: Merc 175, air in fuel system

Injected motors have a VST Vapor Separating Tank which has a float operated needle and seat similar to the float bowl of a carb only much larger. Inside this tank is the high pressure electric fuel pump. This pump is switched on/off by the ECU. A pressure regulator is used to maintain pressure at a specific #.

When the key is first turned on the pump should run for 2 - 3 seconds to build pressure, once cranking and running the pump remains on.

Remove the motor cover and listen as you turn the key on, can you hear the pump run?

You can get a high pressure fuel gauge that screws onto the fuel rail and check pressure, if none or lower than spec then the fuel pump may be suspect. Same when unable to reach WOT RPM, check fuel pressure.

Air in the system should bleed out at the VST pretty quickly.