Tweet
Since this forum helped me, I wanted to post this saga so that maybe it can help someone else. Bottom line: it was the check valve. Hat-tip to RODBOLT.
The story. 2004 F225 TXRC on 2004 Parker 25SE. Following a lengthy stay at the mechanics shop to install the famed exhaust kit (yes there was corrosion), I threw the boat into the water. Start-up was instant and she idled smoothly. After about 5 minutes at idle at the dock, the engine started to run rough and sputter; after another minute the engine stalled out.
After researching this forum, I believed the cause as either the LP pump, LP check valve, or air leaks or restrictions somewhere between the fuel tank and the LP pump intake, or a combination of any or all of the above.
My approach was to start with the easy and less costly stuff first. I proceeded to vacuum and pressure check each section of the fuel system (withdrawl tube, connection points, main fuel tank check valve, RACOR, pump bulb, on-engine fuel filter, et.) with a Mightyvac (purchased specifically for this project; well worth it). I found that the plastic fuel tank withdrawl tube leaked at the connection point of the tube and the aluminum elbow fitting, and at the NPT thread of the main fuel tank check valve, both of which I replaced. After the replacement, the fuel system from pick-up tube to engine fuel filter proved to be airtight (held vacuum (15 mm HG) and pressure (15 psi) constant for well over 30 minutes).
I then checked the ‘flow resistance’ of the fuel system by connecting an external 12 volt fuel pump to the engine side of the engine fuel filter. The external fuel pump, even when 3 feet above the fuel filter was able to draw fuel from the boat’s fuel tank with little problem. I used a small section of clear tubing to connect the external pump to the engine fuel filter; this let me watch for air bubbles coming through the fuel line; there were very few to no bubbles.
The next step was now to investigate the LP pump and check valve. I bypassed the entire fuel system upstream of the engine fuel filter by connecting a portable outboard fuel tank to the engine fuel filter. (As an aside, I did all this work in my driveway; I built an engine test tank because my engine just doesn’t like pumping water from ears; the test tank was definitely worth building as I can use it also in the future). During this test, I varied the height of the portable tank from above the fuel filter (to get a gravity feed) to roughly 3 feet below the fuel filter (simulating the vertical distance from the boat’s actual pick-up tube bottom to the fuel filter that the LP pump would have to lift). The engine seemed to idle fine in this configuration regardless of the tank height. Hence, this test seemed to indicate that the minor air leak at the withdrawl tube was the cause of the stalling. A difference I saw, though, was how full the engine fuel filter would maintain itself correlated to the height of the fuel tank.
So I primed and reconnected the entire fuel system, started the engine and watched as the engine started to sputter and unfortunately…stall.
I then removed the check valve and ordered a new one. Expensive component. Using the Mightyvac, the old check valve popped open at 10 psi, proceeded to rapidly leak down until the pressure was around 4 psi, then continued to leak (but at a slower rate) down to 1 psi. When I re-pressurized the old check valve, I could not even get the pressure up to 8 psi; the check valve just kept leaking back down to 1 psi. The point here is that the check valve operated somewhat correctly one time, then leaked the rest of the time. Also of note, there is a big difference in check valve response using air and liquid (I used water). The liquid gave a better response; air just leaked by. Upon arrival, the new check valve, using water to test, popped open very precisely and crisply at 11.5 psi then closed crisply at 11 psi with no subsequent leakage. Very noticeable difference between old and new check valves. Even checking the new check valve with air indicated a better response (open at 11 PSI; leak down to 4 PSI then close).
After installing the new check valve, she idled very smoothly. In the end, I should have started with the check valve, but I wanted to and did proof out the entire fuel line from tank to LP pump eliminating an air leak. Also, I am surprised the engine maintained idle with the portable fuel tank. In my mind, the fuel flow resistance (caused by length of draw) is much less using the portable fuel tank. Hence, I believe the poorly functioning check valve combined with the long fuel line with multiple resistance exacerbated the fuel starvation problem.
Hope this helps.
The story. 2004 F225 TXRC on 2004 Parker 25SE. Following a lengthy stay at the mechanics shop to install the famed exhaust kit (yes there was corrosion), I threw the boat into the water. Start-up was instant and she idled smoothly. After about 5 minutes at idle at the dock, the engine started to run rough and sputter; after another minute the engine stalled out.
After researching this forum, I believed the cause as either the LP pump, LP check valve, or air leaks or restrictions somewhere between the fuel tank and the LP pump intake, or a combination of any or all of the above.
My approach was to start with the easy and less costly stuff first. I proceeded to vacuum and pressure check each section of the fuel system (withdrawl tube, connection points, main fuel tank check valve, RACOR, pump bulb, on-engine fuel filter, et.) with a Mightyvac (purchased specifically for this project; well worth it). I found that the plastic fuel tank withdrawl tube leaked at the connection point of the tube and the aluminum elbow fitting, and at the NPT thread of the main fuel tank check valve, both of which I replaced. After the replacement, the fuel system from pick-up tube to engine fuel filter proved to be airtight (held vacuum (15 mm HG) and pressure (15 psi) constant for well over 30 minutes).
I then checked the ‘flow resistance’ of the fuel system by connecting an external 12 volt fuel pump to the engine side of the engine fuel filter. The external fuel pump, even when 3 feet above the fuel filter was able to draw fuel from the boat’s fuel tank with little problem. I used a small section of clear tubing to connect the external pump to the engine fuel filter; this let me watch for air bubbles coming through the fuel line; there were very few to no bubbles.
The next step was now to investigate the LP pump and check valve. I bypassed the entire fuel system upstream of the engine fuel filter by connecting a portable outboard fuel tank to the engine fuel filter. (As an aside, I did all this work in my driveway; I built an engine test tank because my engine just doesn’t like pumping water from ears; the test tank was definitely worth building as I can use it also in the future). During this test, I varied the height of the portable tank from above the fuel filter (to get a gravity feed) to roughly 3 feet below the fuel filter (simulating the vertical distance from the boat’s actual pick-up tube bottom to the fuel filter that the LP pump would have to lift). The engine seemed to idle fine in this configuration regardless of the tank height. Hence, this test seemed to indicate that the minor air leak at the withdrawl tube was the cause of the stalling. A difference I saw, though, was how full the engine fuel filter would maintain itself correlated to the height of the fuel tank.
So I primed and reconnected the entire fuel system, started the engine and watched as the engine started to sputter and unfortunately…stall.
I then removed the check valve and ordered a new one. Expensive component. Using the Mightyvac, the old check valve popped open at 10 psi, proceeded to rapidly leak down until the pressure was around 4 psi, then continued to leak (but at a slower rate) down to 1 psi. When I re-pressurized the old check valve, I could not even get the pressure up to 8 psi; the check valve just kept leaking back down to 1 psi. The point here is that the check valve operated somewhat correctly one time, then leaked the rest of the time. Also of note, there is a big difference in check valve response using air and liquid (I used water). The liquid gave a better response; air just leaked by. Upon arrival, the new check valve, using water to test, popped open very precisely and crisply at 11.5 psi then closed crisply at 11 psi with no subsequent leakage. Very noticeable difference between old and new check valves. Even checking the new check valve with air indicated a better response (open at 11 PSI; leak down to 4 PSI then close).
After installing the new check valve, she idled very smoothly. In the end, I should have started with the check valve, but I wanted to and did proof out the entire fuel line from tank to LP pump eliminating an air leak. Also, I am surprised the engine maintained idle with the portable fuel tank. In my mind, the fuel flow resistance (caused by length of draw) is much less using the portable fuel tank. Hence, I believe the poorly functioning check valve combined with the long fuel line with multiple resistance exacerbated the fuel starvation problem.
Hope this helps.