Fuel Flow gauge fluctuation

[KenFlo]

I throw this out there to the community to see if anyone has any ideas.  My LH fuel flow gauge fluctuates after about 10 minutes into the flight at fuel flows above 200 PPH.  This has been an on-going problem and seems nothing can resolve it.  I think the previous owner's shop struggled with it, Byerly fixed it temporarily during the pre purchase 150 hour, and now my shop has done all of the trouble shooting again and yet it will not go away.  We have swapped gauges, swapped sending units, tried a working ECU, Byerly even replaced the wire (that temporarily fixed it) but nothing seems to permanently fix it.  Any ideas from the Commander gurus out there?

[donv]

By "fluctuate" what do you mean?

Mine sometimes drop to zero and come back. They never go above the actual fuel flow, however.

Do you have any other ways to read the fuel flow? In my airplane, the Garmin units are connected to the fuel flow, and I can read it on them (in my case, they never wobble). Another thing to check is the behavior of the fuel counter. It should reflect the reading of the fuel flow gauges, unless the gauge itself or the associated wiring is the issue.

On my airplane, it usually does it after the airplane hasn't flown for a few weeks. After an hour or two, it works normally from then on.

[KenFlo]

Yes, never above the actual fuel flow but from there down to zero.  And usually when fuel flows are above 200 PPH.  The fuel counter is not accurate anymore, it reads low totals.  I think I have a wiring issue that I plan to address during annual.  Thanks for the info....

[donv]

If the fuel counter reads low, that tells you it's either a transducer problem or something in the wiring from the transducer to the cockpit. Cannon plugs are often the culprit for this sort of thing.

Generally speaking, what you are seeing is that the resistance somewhere is just a bit too high, and that can be really hard to track down.

[KenFlo]

Thank you Don...I will have them replace the cannon plug with new and then wiring at my annual.  I appreciate the insight.

[Bruce Byerly]

Ken - if we fixed it, albeit temporarily, then we are on the right track. I do know a lot of time was spent on it. I would fear paying to have someone else try to learn the system, then potentially starting over with a Service Center.

[KenFlo]

Thanks Bruce...I am waiting until annual and having them replace the wire again.  That was the fix last time.  It must be crimping somewhere in the fuselage.  It works great for the first five minutes, then it starts the fluctuation.  Could be a heat problem and the wire needs shielding.

[Bruce Byerly]

Thanks Bruce...I am waiting until annual and having them replace the wire again.  That was the fix last time.  It must be crimping somewhere in the fuselage.  It works great for the first five minutes, then it starts the fluctuation.  Could be a heat problem and the wire needs shielding.

I understand that’s frustrating Ken.  Sorry you’re chasing that ghost but I’m sure it can be resolved.

[donv]

When mine gives me issues, it's usually a sign I haven't flown the airplane in a while! Once I fly a few legs, it settles down.