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Fuel Flow Calibration Creep

snopercod

snopercod

Well Known Member
I have a JPI EDM-700 with fuel flow and it seems like every few months when I check the calibration, I have to adjust the K-factor. The adjustments are all in the same direction - I'm using more than the JPI indicates. This last time, after a 43 gallon fill up, I'm down to 14 gallons actual and my JPI says I should have 19 remaining. Is it normal for fuel flow sensors to creep like this? I haven't been using the boost pump which I know will effect the readings. I'm pretty sure my sensor is a FloScan rather than the "Red Cube". Carbureted engine.
 
Dynon experience

Do not know about JPI but my experience with the flow sensor provided by Dynon with the EMS D120 is that it has stayed within 2/10 ths of a gallon for the last 10 years and 500 hours. I did adjust the K factor a couple of times (once after replacing the facet boost pump) but overall very stable.

I remember reading years ago that turbulent flow around the fuel selector valve and the actual flow sensor position could impact the accuracy of the readings.
FWIW
Figs
 
Where the sensor is located in the system and how it's mounted can make huge difference on it's accuracy. The installation instructions are not suggestions, they should be followed a close as possible. I've seen this happen.
 
FasGlas said:
The installation instructions are not suggestions, they should be followed a close as possible. I've seen this happen.
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I hear you, but the unit was (temporarily) dead-nuts-on for a couple years with the same installation. This is a long-term creep. I did NOT follow the instructions, because it was impossible to comply. I even called JPI. If you're familiar with carbureted Lycomings, it's just not possible to route the fuel line horizontally for 18" between the mechanical fuel pump and the carburetor. The fuel pump is right above the carburetor and back about 6". I did the next best thing and installed my sensor in a horizontal line between the Facet boost pump (right side of firewall) and the mechanical fuel pump (left side of engine). It's been working just fine except for the calibration creep. This concerns me because, having no fuel gauges in my wing tanks, I rely on the JPI for total fuel quantity. (I have a sightglass on my main tank which feeds the engine so I'm always good for two hours.) Thanks for your thoughts.
 
snopercod said:
I hear you, but the unit was (temporarily) dead-nuts-on for a couple years with the same installation. This is a long-term creep. I did NOT follow the instructions, because it was impossible to comply. I even called JPI. If you're familiar with carbureted Lycomings, it's just not possible to route the fuel line horizontally for 18" between the mechanical fuel pump and the carburetor. The fuel pump is right above the carburetor and back about 6". I did the next best thing and installed my sensor in a horizontal line between the Facet boost pump (right side of firewall) and the mechanical fuel pump (left side of engine). It's been working just fine except for the calibration creep. This concerns me because, having no fuel gauges in my wing tanks, I rely on the JPI for total fuel quantity. (I have a sightglass on my main tank which feeds the engine so I'm always good for two hours.) Thanks for your thoughts.
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If the sensor has been accurate for 2 years with no other changes to the installation I'd try another sensor or send yours back to JPI and have them do a long test on it. Floscans are pretty durable but any of them can get clogged or get some damage to the jewels. Checking your wiring to make sure you don't have an intermittent on any of the three wires would be a good place to look. Missing pulses will do just what you have a problem with. Look at the fuel flow with the JPI data program and see if there's drops.
 
Sender sends a pulse (possibly multiple) for every rotation of impeller. If the bearings start to go or you have junk build up, it creates a resistance to spinning. This would cause the impeller to spin fewer times for the same amount of fuel, giving you the readings you are getting.

I would try cleaning it first. If it doesn't improve, it is probably the bearings are going bad. The red cube uses jeweled bearings, so they must be resistance free to operate properly
 
It's hard to figure that a sender could wear out after four years, but I'll certainly consider that possibility. Thanks.
 
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