Simrad Fuel Flow Sensor Calibration

[Thekaj]

I recently installed Simrad fuel flow sensors on both engines (325 Aft Cabin with 350 XL Crusaders), and took her out for the first time this season. On both the out and back, I had the port engine report using about 9.7 gallons of gas each way, while the starboard only reported about 3.5 gallons used each way. It'll be easy enough to conclusively prove this next time I fill up, but I'm about 98% certain that the starboard sensor was WAY off. The 9.7 gallons definitely seemed right for the distance and throttle I was at. And unless the tachometer, throttles, and my ears were all deceiving me, both engines were running at the same speed. Certainly not enough difference to only be sipping a third the amount of gas.

Next time I'm at the boat, I will be double-checking to make sure the sensor is pointing vertically as instructed, and I didn't do something stupid like install it backwards. But does anyone else have experience with these sensors (or others like it) to know if they can simply be that far off in terms of initial calibration? It's a rather simple matter to recalibrate it when I fill it up next time. But my concern is that it's so far off right now, that it might be a fundamental issue with the sensor, and no calibration will will make it better. Although the fact that it recorded nearly the same amount of gas used both coming and going seems to indicate that it's at least consistently inaccurate now.

[bud37]

Was there anything in the install instructions about distance from the engine fuel pump if you have the mechanical pump on the engine ? You will never get both engines the same as there many variables ( wind , current ,props ,state of tune etc ) but close is good. How do the real time gph numbers compare as you are running ?

[Thekaj]

I'll have to double-check the instructions, but I don't recall any distance from fuel pump rule. It was mainly make sure that it's on the inside of a fuel filter, and in a vertical orientation. I've got both sensors essentially in the same spot on the fuel line.

And yeah, I definitely don't expect them to be drawing the same amount of fuel. But if it's off by a factor of 3, with it claiming I'm using LESS fuel than it really is, that's worse than useless, in giving me a false sense that I've got way more gas in the tank than I actually have. I'll see if I can get the display to show both sensor GPH measurements. I had it displaying the port engine MPG on our trip, and only noticed the difference when I pulled up the after-trip numbers. But the port engine numbers were definitely stable the whole trip.

[tomschauer]

I believe the crusaders have a supply and return fuel line if they are fuel injected. If so you need two sensors for each engine and have to set up that configuration within the Simrad system. If this is the case, the one engine may have a return restriction giving you the errant readings.

[Thekaj]

Sadly, the engines aren't FI, so it's a fairly straightforward path from the tank to the filter and then to the pump.