Ovation II - Erratic Fuel Flow Indications (Engine Otherwise Normal)

[G-SLOT]

While flying today, everything was initially indicating normally. At low power cruise, the Mortiz gauge was indicating roughly 10.6GPH while the Shadin gauge was around 10.2GPH (this has been the normal difference in the 12 or so hours I have put on the plane since purchase).

As soon as I switched fuel tanks, the Shadin fuel flow went a little crazy. Initially it was showing zero fuel flow, then it fluctuated pretty wildly, it settled back to normal for a few seconds and then showed somewhere between 0 and about 1.2GPH. During this time, the engine was operating completely normally and smoothly and the Mortiz gauge did not fluctuate at all.

I ran the Shadin gauge through its test function and it tested fine. Tried switching tanks, changing power, etc and nothing helped. The engine continued to run smoothly and normally and the Mortiz gauge indicated normally too.

I landed, uploaded some fuel and, when I started up to taxi back to my parking spot, neither the Shadin nor the Moritz gauges registered anything - both showed 0.0GPH fuel flow (engine was running fine during taxi and no other indications of anything amiss.

I'll be getting the mechanics to look at this asap but I wondered if anyone had any thoughts they could share in the meantime.

Do the Shadin and Mortiz gauges use the same transducers? Are there parts common to both units? The fact that the issue seemed to coincide with switching tanks makes me wonder if some piece of debris may have become caught up in the works (both tanks tested fine pre-flight).

Hopefully nothing too serious but keen to get sorted.

Best wishes to all for the holidays,

Tim

[ArtVandelay]

Did you try turning on the electric boost pump?

Could it just an air bubble in the lines? Did you do any work on the fuel system lately?

The fuel low transducer should be easy to find, just trace the fuel hoses back from the engine.

I believe the transducer should be mounted horizontally in a certain orientation for best results.

 

 

Tom

 

[G-SLOT]

Yes, I tried the low boost a couple of times. Registered an increase in fuel flow on the Moritz gauge but nothing on the Shadin. Didn't try the high boost in flight.

[tmo]

Do both gauges use the same transducer?  If so, I'd look for a ground or signal wire issue.

[alextstone]

Here's the solution to all avionics related problems....

[G-SLOT]

35 minutes ago, tmo said:

Do both gauges use the same transducer?  If so, I'd look for a ground or signal wire issue.

Yes, that's an excellent question and hopefully someone will know.

Given the Shadin and Moritz gauges both indicated a slightly different fuel flow reading, I'm wondering if they are different transducers, though perhaps there's just some internal K-factor setting that's different. 

[carusoam]

We have two threads going today regarding cleaning the fuel flow transducer...

The transducer signal can easily be shared by two displays...

They get dirty with time... the little wheel with a magnet on it gets stuck... and shows a lower than normal FF, or zero in this case... (update: some sensors are light based emitters/receivers on the paddle wheel set-up)

The two displays showing different numbers is a quirk... each device has a K-factor for calibration... one or both displays needs it’s cal checked....

PP thoughts only, not a mechanic..

Best regards,

-a-

[Niko182]

When i installed the JPI900 in my aircraft, i learned that my moritz showed 1.3 gallons per hour more than the JPI. I had 2 shops double check and both said the JPI was correct. If the shadin has only been installed for 10 to 12 hours, it wouldnt be a giant coincident that both are failing. One being the the moritz gauges arent veey reliable, and 2 being the shadin might have had an instalation area. The fuel tranceducers are in the same area, so it wouldnt be surprising that the issue for both of the gauges is caused by the same problem. Good luck. If you have the cash reserves, id get rid of the Moritz and the shadin and just install a jpi900. Mine installed was 7amu, and it can be a lot cheaper if you do a lot of the work yourself. You might get a grand or 2 for the moritz and the shadin fuel flow. Last i saw, a guy sold his old moritz gauges on ebay for 3 grand about 8 or 9 months ago.

Edited December 24, 2019 by Niko182

[G-SLOT]

From what I can tell through the POH schematics, there is just one transducer; however, the POH itself does not contain any sort of supplement for the Shadin (which I believe was factory installed) so it might have also omitted depiction of a second transducer from the schematic. No doubt the mechanics will establish that very quickly.

I'm hoping this is something simple but the medium to longer term plan is to replace the Shadin, Moritz gauges and EDM700 (which does not have any fuel flow data) with a JPI 900 or 930.

[hypertech]

Not a Shadin, but I had this on my JPI.  The fuel flow went a little crazy but the engine ran fine and no fluctuation in EGT or CHT, so I figured it was an indication problem, landed and made arrangements to install a fuel pressure sender so that if I ever get a wonky fuel reading again I've got something to compare it to.

Fortunately, the fix was very cheap.  The bolts holding the mounting plate to the firewall had gotten a little loose.  Tightened them up and its back to being rock solid.  Turns out, the senders can be very sensitive to vibration.  I'd check the sender mounting to make sure everything is tight before anything else.

[G-SLOT]

Quick update on this in case it's useful to anyone else:

I ended up replacing my transducer. Everything works well now.

Although, when the problem first presented itself, the fuel flow on the Moritz gauge continued to register whereas the fuel flow on the Shadin gauge did not, it is a single transducer (attached to the firewall) that sends information to both gauges.

I don't think I'll ever know precisely what the problem was but it wasn't a terribly expensive fix (though I haven't got the bill yet).

[Gagarin]

Remove the fuel flow transducer and spray carburetor cleaner on both ends. Blow by mouth to hear the spinning rotor. Problem solved

[jetdriven]

You should read what JPI says about their Floscan transducers, it has a big tag on it says NEVER BLOW AIR THROUGH in capital letters. And to top it all off, some carb cleaners can damage the turbine wheel inside there, you know it’s plastic.

[PT20J]

The transducers have a rated life of something like 16,000 hrs, so you would think they would last forever. But, when only run intermittently a few hundred hours a year, they don’t seem to last anywhere near that long. Tech at JPI told me that their experience is that they get flakey after about 20 years in service. 

You can try soaking them in Hoppes No. 9, or spraying them with carb cleaner. I guess you could even try WD-40 if that’s your thing. But my experience is that these shade tree mechanic ‘fixes’ only make it work for a little while, if at all. The things are bathed in gasoline which is a pretty good solvent. The transducers are not that expensive as airplane parts go. Just don’t spin a good one with air, and do follow the installation instructions. 

Skip

[ilovecornfields]

I had almost the exact same thing happen after the last annual. It was a loose cannon plug in the engine compartment just on the other side of the firewall. I tightened the plug and the problem went away. If you can find the fuel flow transducer I would trace back the electrical connections and make sure they’re tight.

[Guest]

8 hours ago, jetdriven said:

You should read what JPI says about their Floscan transducers, it has a big tag on it says NEVER BLOW AIR THROUGH in capital letters. And to top it all off, some carb cleaners can damage the turbine wheel inside there, you know it’s plastic.

You can restore the plastic with a good soaking in some WD40.

Clarence