Digital Fuel Flow Indications fluctuating

[Rick A]

The Insight G-2 engine monitor has shown a very solid and predictable fuel burn indication since installed around 8 years ago.

Recently I've noticed fuel flow fluctuates a couple of gallons per hour during climb-outs and leaning, then once leaned out during cruise occasionally fluctuates a few tenths of a gallon. The fluctuations have never occurred like that in the past.

Fuel pressure and true airspeeds are normal, and it sounds and runs fine. There are no noticeable leaks or fuel smells right after shutdown. Peaking around with a flashlight shows nothing unusual.

Could this be caused by a bad connection or a fuel flow sensor going bad? Or is it something that I should be concerned about and dig deeper before the next flight?

A retired A&P friend says don't worry about it. When the sender finally dies then replace it... says the fact the original performed normally for 8 years was great service. Says when it's de-cowled during the next oil change check the wires and any crimps for looseness.

What say you?

 

[StraightnLevel]

Check the ground connection. The Insight systems are sensitive to ground issues. [I have a G3 in my Bonanza and fought this battle last year.]

 

[Bell206]

Could this be caused by a bad connection or a fuel flow sensor going bad?

What type of fuel flow sensor does it use?

 

[Rick A]

What type of fuel flow sensor does it use?

It uses a Paddle Wheel Turbine type FF sensor. Without looking at the part, a little research shows it to be manufactured by Insight Avionics p/n 1000-004A-3.

 

[Let'sgoflying!]

My fuel flow indication started being intermittent this year, I did some connector and inspection cleaning b/c the FloCal was only 2 years old - then the display completely quit so I put in a new sensor/sender and it's fine again.

 

[Bell206]

Insight Avionics p/n 1000-004A-3.

Is your fuel pump(s) of similar age as the sensor? Turbine and vane type sensors tend to wear over time due to having mechanical parts. If the wiring is good on your next check, perhaps contact their tech support and see if you can have this one rebuilt or exchanged during the next annual.

 

[Rick A]

Is your fuel pump(s) of similar age as the sensor? Turbine and vane type sensors tend to wear over time due to having mechanical parts. If the wiring is good on your next check, perhaps contact their tech support and see if you can have this one rebuilt or exchanged during the next annual.

Good idea, I'll check with Insight. The new G2 monitor with sensor was installed eight years ago, replacing an Insight monitor (without FF) that lasted over 22 years before the display quit. Figured that was a good run and didn't bother shopping around, just gave them the business.

 

[Rick A]

The sensor can be serviced by Insight if they allow the return (which in my case is unlikely).

Insight Avionics manufactures all its sensors in-house and provides one year or 1,000 hours warranty coverage on probes, harnesses, and sensors from the date of purchase. The company offers factory authorized service and warranty center capabilities for its products, which includes repair or replacement of defective items. Insight provides bench service and re-certification to OEM specifications through their service centers. Pilots and mechanics are advised to consult Insight TECH Support or the specific Probe Support guidelines for diagnostic steps before initiating a return.
https://www.insightavionics.com/warranty.htm
Insight Avionics 1000-004A-3 failure causes
Based on owner reports and manufacturer documentation, the Insight Avionics part 1000-004A-3 (FT-60 Red Cube, Inline Mount, 201 Fuel Injected) has several well-documented failure modes:

Mechanical / Internal

• Turbine or impeller seizure — debris or fuel varnish can jam the paddle wheel on its jewel bearings, causing a zero or erratic reading.
• Optical sensor degradation — the internal light source or photocell can burn out, producing no output signal.
• Heat exposure — proximity to hot engine components accelerates failure; wrapping the unit in fire sleeve is a common mitigation.

Electrical / Wiring

• Intermittent or broken wire connections at the connector or solder joints, often caused by vibration. This is the single most commonly reported "fault" that turns out to be external to the sensor itself.
• Poor grounding — high resistance at the ground path can cause erratic or zero readings.
• Electrical noise from nearby ignition, alternator, or radio equipment falsely triggering the open-collector output.

Installation-Related

• Turbulence from elbows, valves, or pumps too close to the sensor (spec calls for ~5–6" of straight line on each side).
• Wrong orientation — the sensor must be mounted with the electrical wires pointing up to vent trapped bubbles.
• Upstream of the fuel pump — can cause vapor lock and jumpy readings.
• Thread sealant contamination — Teflon tape or pipe dope that migrates into the body can wrap around the rotor or clog an orifice.

Age / Wear

• While the rated life is 10,000 hours minimum, owner reports show units failing anywhere from ~15 hours to a few hundred hours, with the most common symptom being a gradual drift in indicated flow or an eventual complete loss of signal.

In most cases, the sensor itself is the least likely culprit — wiring, connectors, and installation geometry account for the majority of reported "failures."