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speaking of floscans

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bobct

Advanced Contributor
I installed floscans last year and have a nagging issue. BTW, I went with the 0-32 twinscan unit on my carb'd 454's.

My issue is the port side needle randomly floats all over the place so I've never gotten an accurate reading. Sometimes it'll settle down and I think it's close to the port side consumption. The Stb side is fine. I called Floscan and they sent me another sensor but that didn't make any difference.

I think the general consensus is a tiny air leak somewhere between the tank and the sensor. Obviously no fuel leaks. I have copper line from the tank to the crossover valve and then everything past that point upstream to the engine is new. I plan on replacing the copper with flex line but wasn't going to until the fall when I come out. In the meantime, is there anything I could use to try and seal all of the joints from the outside in the meantime? I was thinking of trying rescue-tape?

I've checked and tightened everything. This would be a lot easier if it was a fuel leak, air is hard to detect :)

The only other variable is the way the Racors are mounted. Flo-scan calls for the sensor to be mounted so that it's always full of fuel and pumping slightly "uphill". Instead of using another 45 degree fitting to accomplish that, I have the Racors mounted with a slight tip to one side. This setup has worked fine on the Stb fine since I did the install but thought it was worth mentioning.

Thanks!
Bob
 
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how much variation and for how long equates to "floats all over the place"?

As far as sealing the copper lines, you could try a couple coats of paint or some air duct mastic compound. Copper should be flared and they usually don't leak when assembled properly.

I'm guessing you have alread swapped the sensor-gauge connections to verify the issue is in the plumbing and not the electronics?
 
Try a short length of clear pvc tube just before the sensor to check for bubbles. How close is the mechanical fuel pump? You might need the pulsation dampner, although it does sound more like air.
 
yes, I did swap the electronics from side to side and verified it's a plumbing issue. At idle, it will range from 0 to around 12 GPH. At cruise speed, it will sometimes go all the way to 32 (max) and then float back down. There doesn't seem to be a real pattern

I have a big 232 micron pre-filter on each side before the sensors so I don't believe I need pulsation dampener(s). The sensor is sandwiched between the pre-filter and the Racor.

I could try the clear tube test. What about some silicone sealant if I cleaned the joints with acetone?
 
Nope. RTV is a no-go with gas. If you see air, keep moving the hose towards the tank to find out where the air leak is. Crossover and shutoff valves are notorious for this (stem packing I think).
 
Make sure you put some oil on the fuel filter gaskets (all of them) - you can get tiny air leaks from this also - says so in the floscan manual

Not sure about the single unit - but the twinscan with a totalizer - if you hit the reset switch twice the instrument goes into test mode. If both needles are the same - the problem is probably an air leak
 
I had to remove a shuit of valve upstream (before) my flowmeter to get it reading correctly. The fuel pump would suck enough air through the valve to mess up the readings--hard to believe but true. You might have to relocate yours before ANY shut off or other valves to get air-free readings.

Jeff
 
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