Fuel Flow Transducer

[peevee]

Our has been fluctuating and now is just completely intermittent. 0 or normal and randomly decides to switch from one to the other. No word from the mechanic on a cause. 

Edited August 3, 2016 by peevee

[One Whiskey Hotel]

Don Muncy: how has your transducer been holding up since cleaning? I have a 231 with a likely failed transducer as well, considering neither my ships gauge nor EDM700 are registering fuel flow. Wondering if cleaning the transducer as Jose suggested is proving to be a sustaining repair.

[DonMuncy]

Unfortunately, the problem has persisted.

Right after I discovered the problem, my avionics guys found it in-op, and swapped to a different transducer. It then worked, so they deduced it was merely a bad transducer. That is when I got on the forum and began seeing where others got good results with carb cleaner. That is when I tried it. After the cleaning, I could blow through it and hear the "wheel" spin. (Unfortunately, I had failed to check that before I cleaned it.) 

Because it originally appeared the FF worked properly when I started an taxied, I thought perhaps it worked at low readings and failed at higher ones. So after I cleaned it, I ran a high speed taxi, up to about 26 GPH, and declared it fixed (on this forum). But then, the next flight, it was okay when I started, but failed in the air. I have concluded that we have no way of knowing whether it is the transducer or the instrument. I am leaning toward the instrument, as it seems unlikely to me that the wheel would turn freely after carb cleaner, and then immediately stick again. I am now learning the transducer (201BM) costs in the $6 and $7 hundreds. I am seriously considering sending the instrument in for a check-up. I still have not made a final decision.

[Zwaustin]

We goofed around with mine for almost two months. Cleaning the transducer didn't work so I ordered a new transducer thinking that was it and after install it would read normal, sometimes zero and sometimes just goofy numbers like 2.3 and 4.9 at normal cruise so back to square one and returned the transducer less a re stock fee . I then pulled the Hoskins FT101 unit and had it overhauled at instrument tech in Dallas for roughly $600.00 thinking this had to be it. They allegedly duplicated the problem and sent it back freshly overhauled with a one year warranty. After reinstalling it seemed to read fine and then on my next long trip it was back to the normal readings coupled with sporadic goofy readings of low numbers and some off the wall readings. I could tell when it was reading accurately for short periods knowing my fuel burn but it just wasn't reliable. We checked all the wiring and it seemed to be fine. Sent the unit back to Dallas for re examination since we know it was not the transducer. They flow tested it for hours and even facetimed me to show me the set up and what not. They also decided that they weren't working on these units anymore and said that after this last test they would have no one to warranty my unit which I was not happy about. I was at wits end now and thinking I didn't want to dump another wad of cash on a new fuel flow system when this one already sat nicely in the dash and I had spent nearly 700 total trouble shooting it. When the mechanic went back to re wire the connectors at firewall he said he found one that was suspect. Haven't had an issue since. With all this being said I feel yalls pain, double and triple check that wiring, might save you 700 and many headaches as I can't help but to think it was an unseen wiring issue all along. 

[DonMuncy]

1 hour ago, Zwaustin said:

We goofed around with mine for almost two months. Cleaning the transducer didn't work so I ordered a new transducer thinking that was it and after install it would read normal, sometimes zero and sometimes just goofy numbers like 2.3 and 4.9 at normal cruise so back to square one and returned the transducer less a re stock fee . I then pulled the Hoskins FT101 unit and had it overhauled at instrument tech in Dallas for roughly $600.00 thinking this had to be it. They allegedly duplicated the problem and sent it back freshly overhauled with a one year warranty. After reinstalling it seemed to read fine and then on my next long trip it was back to the normal readings coupled with sporadic goofy readings of low numbers and some off the wall readings. I could tell when it was reading accurately for short periods knowing my fuel burn but it just wasn't reliable. We checked all the wiring and it seemed to be fine. Sent the unit back to Dallas for re examination since we know it was not the transducer. They flow tested it for hours and even facetimed me to show me the set up and what not. They also decided that they weren't working on these units anymore and said that after this last test they would have no one to warranty my unit which I was not happy about. I was at wits end now and thinking I didn't want to dump another wad of cash on a new fuel flow system when this one already sat nicely in the dash and I had spent nearly 700 total trouble shooting it. When the mechanic went back to re wire the connectors at firewall he said he found one that was suspect. Haven't had an issue since. With all this being said I feel yalls pain, double and triple check that wiring, might save you 700 and many headaches as I can't help but to think it was an unseen wiring issue all along. 

Any details about that connector. I haven't started to look yet, but all hints are appreciated.

[carusoam]

The system is a simple pulse counter with memory and a display.

Since the little turbo wheel can get dirty and stick, it is always good to give it a cleaning.

Consider anything that can weaken or interrupt the pulses coming from the sensor.  Check to see if you can clean any connectors from the sensor to the panel unit.

A mechanic with an oscilloscope could be very helpful.  Not sure if your mechanic has an o scope.  Modern high tech voltmeters have these kind of skills nowadays...

PP thinking out loud,

-a-

[Zwaustin]

10 hours ago, DonMuncy said:

Any details about that connector. I haven't started to look yet, but all hints are appreciated.

I am no mechanic but mine told me it was at the firewall and there was a pin connector that was just ever so sightly loose. Once he "tweaked" this wire i haven't had an issue in a couple months or so. This was found as we were re wiring it all to start fresh based on recommendation from Instrument Tech in Dallas after they could not find anything wrong with the overhauled unit. Also possible that a solder has come loose inside your FT-101 Display unit assuming thats what you have. 

[DonMuncy]

My hangar elf took a look today. Wires traced back to the plug going into the firewall. It is a brass looking plug with about 6 wires into it. On the engine side, the plug seems to contain some black caulk looking stuff. The plug itself seems to be made in about three parts, and my elf was not smart enough to be able to disassemble it. Getting to the cabin side of the plug is really tough; either from the top or from underneath.

[carusoam]

That's got to be a plug that hasn't been cleaned in a while. 

-a-

[superfly1]

So my Mooney 231 Fuel Flow Sensor is operating radically.  The analog gauge bounces from 22+ gal down to 10 gal and all around.  The same input is tied to my JPI 830, which mirrors the analog which in this case, bounces around as well.  I had it replaced, and lasted about 3 hours before the same condition repeated itself.  Bouncing around all over the map.  However this time, it would radically read for about an hour in flight, then suddenly straighten out and read correctly.  I have been asking around, a friend of mine who is a mechanic, tells me he has seen this twice before.  It was a result of the fuel flow sensor being installed "backwards".  Anyone else have any experience with this concern?

[carusoam]

Installing a sensor backwards is hard to do when following the instructions...

Easy to check if the pilot can recognize arrows or the words in and out...

The sensor sends signal waves that are counted... a loose or dirty connection may have signals being dropped...

What sensor do you have installed in your plane?

What analog display do you have?

Are both displays reading the same erratic numbers?

Best regards,

-a-

[jetdriven]

On 9/9/2016 at 7:00 PM, DonMuncy said:

Unfortunately, the problem has persisted.

Right after I discovered the problem, my avionics guys found it in-op, and swapped to a different transducer. It then worked, so they deduced it was merely a bad transducer. That is when I got on the forum and began seeing where others got good results with carb cleaner. That is when I tried it. After the cleaning, I could blow through it and hear the "wheel" spin. (Unfortunately, I had failed to check that before I cleaned it.) 

Because it originally appeared the FF worked properly when I started an taxied, I thought perhaps it worked at low readings and failed at higher ones. So after I cleaned it, I ran a high speed taxi, up to about 26 GPH, and declared it fixed (on this forum). But then, the next flight, it was okay when I started, but failed in the air. I have concluded that we have no way of knowing whether it is the transducer or the instrument. I am leaning toward the instrument, as it seems unlikely to me that the wheel would turn freely after carb cleaner, and then immediately stick again. I am now learning the transducer (201BM) costs in the $6 and $7 hundreds. I am seriously considering sending the instrument in for a check-up. I still have not made a final decision.

The EI red cube is much cheaper.  Works just as well or better. 

[carusoam]

Pic of the EI red cube below...

Follow instructions for top and bottom... a gravity related issue.

-a-

https://iflyei.com/wp-content/uploads/FT-60-Info-Rev-F.pdf

[PT20J]

Yeah, I don't think much of the Floscan transducers. My'94 J came from the factory with one driving a Shadin Miniflow-L. It was intermittent when I bought the plane and I tried the "soak it in Hoppes No. 9" trick. Didn't stay fixed. So I replaced it and at the same time removed the Shadin to set the K factor. Hmmm. Original transducer was stamped 28.9. Shadin had a label on it that appears original (numbers were metal stamped into foil label) 33.06. I set the Shadin to 29.0 which was what the new transducer was marked and it read way off. I borrowed a known good Shadin and it read exactly the same as mine. I reset the Shadin to 33.06 and have been tracking it carefully and it varies a bit but is most consistently about 6% lower than actual consumption. Mooney mounts the transducer upside down from Floscan's recommendations and I went to some trouble to remount it and replace the 45 deg elbow on the inlet with a straight fitting. This made absolutely no difference. So, it's possible my brand new transducer is out of calibration, but I doubt it. They are calibrated at 16 gph and I usually run between 8 and 10. I just don't think they are very accurate at low flows. Interested in other's experience.

Skip

Edited January 26, 2020 by PT20J

[jetdriven]

If you have very smooth entry and exit from the transducer it really helps the accuracy at different fuel flows.

My flow scan transducer went bad a few years ago and I replaced it with a red cube. When I install the JPI 830, it came with a brand new flow scan transducer but I just kept using the red cube. So I still have a new flow scan in a box. Those things sell for over $500 now, probably because JPI bought them and now they have a monopoly on it

 

 

[moosebreath]

I ignored the stamped, labeled, and previously calibrated numbers on mine.  I calibrated it by adjusting the K factor until the total fuel usage matched what I had to put back in the tanks.  You of course must take care how you fill the tanks each time.  I parked in exactly the same spot and filled to exactly the same place in each tank by eye for each trial.

It is now accurate to approximately .5 gallons out of 40 repeatedly.  That is 1.25%.  I am not at home just now but I think the Shadin sensor spec is 2% so job done.  I normally run between 10 and 11 gph in cruise and my flow numbers are very close to book figures.

As I recall, my final K value was significantly different than the “calibrated” number also.  It took only two or three trials to calculate the final K value for my installation.  It is a very simple system and responds linearly to changing the K value.

Note to the usual lurkers:  No I am not an authorized instrument shop or have a note from my Mom or the FAA.  I just know how to calibrate the instrument in my installation.

I also put a piece of tape on the top of the Shadin box recording the current K value in case I had to reset it in the future.  It has kept the same accuracy for four years.

 

[PT20J]

K factor is so many thousand pulses per gallon. After the pinwheel, it's an all digital system. Therefore, if the things were accurate, you wouldn't have to mess with the K factor - just set it to whatever is marked on the transducer and DONE. But as the evidence mounts, apparently they are not very accurate (except they probably meet the factory spec of +/- 2% at 16 gph). Mine had a calibration tag that read 28.965. My college professor would have referred to that as being overly precise about something that is fundamentally inaccurate.

Skip

[skykrawler]

Some of these failure modes described imply a loose connection or a wire with an internal fatigue break.   Envision a single pulse being multiplied from vibration causing a poor connection to make-and-break several times.  That could explain crazy high flow rates from time to time.  Doesn't seem likely that a sticking vane would cause high indicated rates.

[Stormy]

I am five years late on this topic.  My fuel flow indicates high, about twice what I'd expect.  That makes the JPI think I have far less fuel than I do, along with dire warnings of impending doom.  I have verified that actual fuel flow is normal, and I am not losing fuel overboard. I am guessing transducer.  JPI and FF display are showing an identical number.  What makes a fuel flow transducer indicate too high?  I wondered if air is being sucked into the fuel line through the selector valve.  But, if the leak were big enough to allow air in, surely it would be allowing fuel to leak out when the aircraft sits.  

[LANCECASPER]

5 hours ago, Stormy said:

 JPI and FF display are showing an identical number.  

My bet is that you have one transducer and your installer split the wiring so they are each getting the same reading. What did they put in for a K factor on the JPI?

[carusoam]

Welcome aboard Stormy!

When a FF system gets installed in a plane...  the K-factor gets adjusted...

It is a precision adjustment that corrects the FF read out to the actual FF...

If your numbers are off by 2X... a quick review of the entire installation might be a good idea...

Best regards,

-a-

[Stormy]

Thanks.  It was working perfectly for the first two years I owned the plane.  On occasion, I have seen it change to a reasonable number for a minute.  So, I don't think the K factor is off.  Once set, it should stay set - I think.  That is why I am looking for failure modes of the transducer that would change the value.  If it were a bad electrical connection, I would expect it to go to zero, not 2X.  I wondered if there is a return FF transducer that might be going to zero, perhaps doubling the indicated FF.  But, I think my 1984 M20K has only one transducer downstream of the fuel pump.  

On 4/21/2021 at 11:18 PM, carusoam said:

Welcome aboard Stormy!

When a FF system gets installed in a plane...  the K-factor gets adjusted...

It is a precision adjustment that corrects the FF read out to the actual FF...

If your numbers are off by 2X... a quick review of the entire installation might be a good idea...

Best regards,

-a-

 

[carusoam]

6 minutes ago, Stormy said:

Thanks.  It was working perfectly for the first two years I owned the plane.  On occasion, I have seen it change to a reasonable number for a minute.  So, I don't think the K factor is off.  Once set, it should stay set - I think.  That is why I am looking for failure modes of the transducer that would change the value.  If it were a bad electrical connection, I would expect it to go to zero, not 2X.  I wondered if there is a return FF transducer that might be going to zero, perhaps doubling the indicated FF.  But, I think my 1984 M20K has only one transducer downstream of the fuel pump.  

 

I see what you are saying...

FF sensors are typically a paddle wheel in the fuel stream...

The sensor is often a beam of light that gets broken each time the wheel rotates...

The gauge counts the pulses and converts it to gph using the K factor...

 

Two common failures for FF sensors... around here.

1) They get dirty and start missing the count... decreasing the FF seen...

2) There is an air leak drawing air into the fuel line... increasing the FF seen...

Often, the FF sensor gets removed and cleaned, and reinstalled...

If you are getting higher than usual FF numbers be on the look out for blue staining around the fuel selector valve and areas like that...

When an air leak is suspected... the mechanic will often take the fuel line off near the engine and run the pump... watching for air bubbles coming through the line...

PP thoughts only, not a mechanic...

Best regards,

-a-

[PT20J]

If it were me, I’d just replace the transducer. That’s the most likely culprit and these things don’t last forever. It would seem unusual for it to read high, but it would be difficult to rig up a test and these things are not that expensive as aircraft parts go. 

I have not been able to get my Floscan 201B transducer to be better than about +/-3% accuracy and I have gone to great lengths to get the plumbing, orientation and electrical noise within specs. I think they are pretty sensitive to fuel flows. They are calibrated at 16 gph and are probably accurate at that flow. If they were accurate, the engine monitors using them would not have procedures for adjusting the K-factor to get the fuel consumption to agree with actual. 

Skip

[carusoam]

Possible name and manufacturer of a FF sensor often used around here... Red Cube, EI?

+1 for horizontal mount, wires up, long straight entry and exit when able... in a place that isn’t hot or vibrating...

PP thoughts only, not a mechanic...

Best regards,

-a-