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twin flowscan needle float

S

slauder

Regular Contributor
I added flowscan a while ago. I sometimes see the needle float way up and then come back to stable level (matching other engine) without moving the throttle/rpm. I attributed to some air. Also when I throttle up to cruse at 3100 I see floating way up and then back down to stable. Air I think. Does this get added to my running total of GPH? Could it be gas and not air I see? It happens on port engine mostly. Both engines sound same.
 
You definitely are getting air sucked in. I had to relocate my sender unit BEFORE all of my fuel shut offs since the pump was sucking air in through them.

Jeff
 
Did you install pulsation dampers? I was told that for my application, the dampers would eliminate any needle fluctuation and the possibility of any bubbles in my system. I have Crusader 454’s with carbs and mechanical fuel pumps.
 
I had the exact same problem, as a matter of fact, I thought someone was replying to my old post when I saw the subject.

This is a really annoying problem, it took me two seasons to figure it out. Anyway, it is air and just because air is leaking doesn't mean fuel will. The problem is every boat is different and it's hard to track down. My setup looks like this:

Tank--->crossover--->10 micron pre-filter---->Floscan sensor--->Racor----->Hard line(s) to carb. Based on my setup, I didn't need pulsation dampers.

All of my fuel line was new/flex hose. The root cause for me was the copper line coming from the tank to the crossover valve. I replaced that with flex hose and it was instantly fixed. After trying everything else, I replaced it sort of taking a shot in the dark but I wanted to replace it anyway. My other side worked right out of the box and still has the copper line which I'll replace this winter. My engines are '88 454's.

Bob
 
bobct said:
I had the exact same problem, as a matter of fact, I thought someone was replying to my old post when I saw the subject.

This is a really annoying problem, it took me two seasons to figure it out. Anyway, it is air and just because air is leaking doesn't mean fuel will. The problem is every boat is different and it's hard to track down. My setup looks like this:

Tank--->crossover--->10 micron pre-filter---->Floscan sensor--->Racor----->Hard line(s) to carb. Based on my setup, I didn't need pulsation dampers.

All of my fuel line was new/flex hose. The root cause for me was the copper line coming from the tank to the crossover valve. I replaced that with flex hose and it was instantly fixed. After trying everything else, I replaced it sort of taking a shot in the dark but I wanted to replace it anyway. My other side worked right out of the box and still has the copper line which I'll replace this winter. My engines are '88 454's.

Bob
Click to expand...

Have 1991 Tiara, 454s with 1 260 gallon tank that splits with hard lines, then into flex to racor paper 10 micron filters, to floscan, to pump (exits back to hard lines), to separator/filters, to rochester.

so I'll see what I can do before the 10 micron racors.

Is the floating being added to the running total (sum GPH for both sides is displayed)???
 
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Personally, I wouldn't run a 10 micron filter BEFORE the fuel pumps. One load of bad fuel and you'd end up starving the fuel pumps, which would lean out the motors and cause burnt pistons. Much safer to run a coarse STRAINER (not filter) of 30 microns minimum before the pump, with a fine filter (10 microns) AFTER the pump.

The reason for the above is that gas is very volatile, meaning it evaporates easily (which is necessary for combustion). This same volatility also means that, if flow restricted on the way to a fuel pump. Instead of flowing it will flash to a vapor, and vapors will not pump. In the old days cars regularly experienced "vapor lock", which was usually cured by cooling the fuel line to the pump with water (or letting the car sit for a few hours to cool off).

Over the years, I've run into countless "mysterious" engine power loss problems that defied resolution: The pump was making good fuel pressure (in the slip), the ignition system was apparently working fine (no hot electronics failures), but the motors lost power now and then for no apparent reason. Guess what it often was!

Jeff
 
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I have encountered the "mysterious" power loss many times on the port engine after coming off plane, and trying to get back on plane after a few minutes of running slow. I never have the issue when planning the first time only on subsequent tries in the same trip. I have changed the pancake filter (113 micron) and water/fuel sep filter. The only thing I've not looked into is a strainer at the bottom of the tank intake, which seems like an impossible endeavor on a Carver 355 aft-cabin with twin 454 XLi.
 
fastjeff said:
Personally, I wouldn't run a 10 micron filter BEFORE the fuel pumps. One load of bad fuel and you'd end up starving the fuel pumps, which would lean out the motors and cause burnt pistons. Much safer to run a coarse STRAINER (not filter) of 30 microns minimum before the pump, with a fine filter (10 microns) AFTER the pump.Jeff
Click to expand...
Jeff, I double checked... I already took your wise advise 4 years ago and have 30's (red) before
 
The "float" will get added to the total...it is nothing more than a simple dedicated computer so it has not "smarts".... need to eliminate the float to get an accurate total. Their calibration procedure should be used after the float issue is resolved.
 
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