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FlyBoyM20J

Fuel flow/pressure transducer

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My Shadin (I believe it is a Shadin, pic below) has been flaking out for months, usually reading close to 0 GPH.  I've searched for this and found a few threads on here but everyone seems to have an actual fuel flow transducer in a loop fed from the port on the side of the fuel distribution unit.

Mine would seem to be a pressure transducer on a dead-end line from the servo.  Can anyone tell me more about this sensor?  (These are pictures from last year - there's a new muffler and a lot of cleanup since then!)

image.thumb.png.ba2211ed0880d63abbc160205ce3b7f3.png

The supply goes back around to the servo here:

image.thumb.png.2f1421853b22a2e6c9ac5b5f3a0f7c71.png

Here's the FF computer in the panel.

image.png.4919e0a118c9e10babfe197b4dfa2229.png

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That’s your fuel pressure transducer, the fuel flow transducer will be on the opposite side in the hose between the fuel pump and the injection servo.

Clarence

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38 minutes ago, M20Doc said:

That’s your fuel pressure transducer, the fuel flow transducer will be on the opposite side in the hose between the fuel pump and the injection servo.

Clarence

Thanks, Clarence!

So, I've been thinking about this backwards...this signal goes to the FP gauge in the cluster set at eye level...and the FF transducer that I'm looking for has yet to be found...by me.  I'll look through more of my past pictures.  I have a habit of taking lots of pictures from many angles almost every time I have the cowling off.  Turns out to be helpful in times like this to go back and browse through them.

Cliff

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I also would pull off the cowl flaps bar hardware and clean it up and repaint it. It’s a bit rusty. You must be very clean when doing oil changes.


Tom

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it may look something like this....usually wrapped in a big fat bundle of orange firesleeve.

 

https://www.aircraftspruce.com/catalog/inpages/edm700transducgrav.php?clickkey=50353

 

might be located on the top of the engine in the line running to your flow divider.  I run a bunch of these in a fleet of aerial survey 172s, every once in a while one will go bad and start to read 0 gph.

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Thanks, Steve!

I guess it must be in this fat bundle of orange firesleeve under C4 running right next to the exhaust riser.

image.thumb.png.75b32f0c8a377143a8dd3013fd3967f1.png

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11 minutes ago, Steve2 said:

 I run a bunch of these in a fleet of aerial survey 172s, every once in a while one will go bad and start to read 0 gph.

sometimes they just get gummed up and an overnight soak in carb cleaner will free the little internal wheel up. YMMV but my last one ran fine until I sold the plane after a soak.

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15 minutes ago, ArtVandelay said:

I also would pull off the cowl flaps bar hardware and clean it up and repaint it. It’s a bit rusty. You must be very clean when doing oil changes. emoji1.png


Tom

It's cleaner now, Tom!  This is all from last year when I was looking under the cowl for the first time.  But yeah, this plane needs paint in more than one place.

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1 hour ago, FlyBoyM20J said:

Thanks, Steve!

I guess it must be in this fat bundle of orange firesleeve under C4 running right next to the exhaust riser.

image.thumb.png.75b32f0c8a377143a8dd3013fd3967f1.png

It should be within the large section of firesleeve with the safety wire wraps. On another note I would not stand the lower cowl on the cowl flaps, it’s hard on the hinges.  Also you might want to add some form of stand off to provide some spacing between the JPI wires and the ignition wires.

Clarence

 

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6 minutes ago, M20Doc said:

It should be within the large section of firesleeve with the safety wire wraps. On another note I would not stand the lower cowl on the cowl flaps, it’s hard on the hinges.  Also you might want to add some form of stand off to provide some spacing between the JPI wires and the ignition wires.

Clarence

 

Wow, thanks for all the help!  My A&P stood the lower cowl up like that one time and I just decided to copy how he did it.  I can see in the picture that it is forcing the cowl hinges to bear a lot of the weight, so I will not do that again.

I also see what you mean about the JPI CHT and EGT probe wires being zip-tied to the ignition wiring.  Chance of inductive coupling is probably high.  I'll correct that.   Is there a standard kind of "stand off" that would go into a bundle like that or should I just find a way not to zip-tie the JPI wires to the magneto wires?

Cliff

 

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1 minute ago, FlyBoyM20J said:

Wow, thanks for all the help!  My A&P stood the lower cowl up like that one time and I just decided to copy how he did it.  I can see in the picture that it is forcing the cowl hinges to bear a lot of the weight, so I will not do that again.

I also see what you mean about the JPI CHT and EGT probe wires being zip-tied to the ignition wiring.  Chance of inductive coupling is probably high.  I'll correct that.   Is there a standard kind of "stand off" that would go into a bundle like that or should I just find a way not to zip-tie the JPI wires to the magneto wires?

Cliff

 

I use Stanley metal drawer corner reinforcers from Home Depot.  Drill one hole to 1/4”, radius the corners with a file and secure them to a rocker cover screw, then use an Adel clamp on the leg to support the JPI wires.

Clarence

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Sensor fun...

FP, fuel pressure... The sensor is connected to the fuel system by a hose...or directly on a port.  Wet on one end, wires on the other end...

older mechanical systems, have a small tube filled with fuel delivering pressure to the back of the gauge in the instrument panel... a pressure sensitive diaphragm moves the needle....

Electrical systems, have a piezo-Electric sensor that sends a voltage signal to gauge... fuel stays on the front of the firewall, less fuel line, more wires...

FF,  Fuel Flow... has fuel flowing through it... Expect a hose in and a hose out... the sensor itself is a paddlewheel and senses the rotation of the wheel. Often a magnet does the work and a small computer does the counting...  PIC is responsible for calibrating the K factor...

Fire safety is important so the hoses and tubes are usually wrapped in a fire sleeve for protection.

FF sensors come with instructions to follow, with guidance on how long the hose should be, both in and out of the sensor... it is good technique to follow a successful install when the guidelines can’t be followed perfectly.

 

EGT and CHT... thermocouple wires are carrying tiny amounts of voltage in them... putting them anywhere near the extremely high voltage ignition wires can accidentally induce unwanted signals into the temperature measurements...

JPI has some instructions to use when the instrument gets installed.  same as above... it is good technique to follow a successful install when the guidelines can’t be followed perfectly.

PP thoughts only, not a mechanic...

Best regards,

-a-

 

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1 hour ago, FlyBoyM20J said:

Thanks, Steve!

I guess it must be in this fat bundle of orange firesleeve under C4 running right next to the exhaust riser.

image.thumb.png.75b32f0c8a377143a8dd3013fd3967f1.png

One last thing, the cabin heater inlet Scat duct normally goes through the cylinder number 2 intake tube, you can see the rub marks. 

It should be secured with Adel clamps.

Clarence

4F31BA59-554E-44CE-A454-423D93F3FCCA.jpeg

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2 minutes ago, M20Doc said:

One last thing, the cabin heater inlet Scat duct normally goes through the cylinder number 2 intake tube, you can see the rub marks. 

It should be secured with Adel clamps.

Clarence

4F31BA59-554E-44CE-A454-423D93F3FCCA.jpeg

Fantastic advice, thanks as always!  I often wonder if the way this engine was maintained by the previous owner's A&P was quite correct.  I've found a number of oddities...some more serious than others.

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38 minutes ago, M20Doc said:

One last thing, the cabin heater inlet Scat duct normally goes through the cylinder number 2 intake tube, you can see the rub marks. 

It should be secured with Adel clamps.

Clarence

We bow down to you, Clarence! :D

I'm also kind of scratching my head about the heater outlet SCAT hose.  on my 86 J, when the hose is routed according to the diagram, it just barely clears the torque tube that controls the cowl flaps, to the point we had to squash it pretty good.  I can't tell how @FlyBoyM20J has so much clearance in his

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I also see what you mean about the JPI CHT and EGT probe wires being zip-tied to the ignition wiring.  Chance of inductive coupling is probably high.  I'll correct that.   Is there a standard kind of "stand off" that would go into a bundle like that or should I just find a way not to zip-tie the JPI wires to the magneto wires?

My JPI wires are inside and ignition wires on the outside:

 

653643eb9ab816f4af537413aeffe428.jpg

 

 

Tom

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2 hours ago, jaylw314 said:

We bow down to you, Clarence! :D

I'm also kind of scratching my head about the heater outlet SCAT hose.  on my 86 J, when the hose is routed according to the diagram, it just barely clears the torque tube that controls the cowl flaps, to the point we had to squash it pretty good.  I can't tell how @FlyBoyM20J has so much clearance in his

Yes, that one is questionable as well.  Normally it’s Adell clamped to the eyelet on the copilots footwell step.  I like to add an additional Adel clamp to the intake tube for cylinder 3 to keep it out of the cowl flap mechanism.

Clarence

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59 minutes ago, M20Doc said:

Yes, that one is questionable as well.  Normally it’s Adell clamped to the eyelet on the copilots footwell step.  I like to add an additional Adel clamp to the intake tube for cylinder 3 to keep it out of the cowl flap mechanism.

Clarence

That's what I saw as well.  He must have his adel-clamped or ty-wrapped to follow the #3 intake tube.

IMG_2086.PNG

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Here's a better view of the heater scat tube.  Please keep in mind that the plane came from the previous owner in this configuration and these pictures were from last year, when I'd had the plane in my possession for about 4 months and hadn't done much work or cleaning.  I think this might have been from the first oil change I did myself.  Historically, the plane was leaking a fair amount of oil from the old rocker cover gaskets, so this was just after I'd had them replaced with silicone ones and some of the old leaking oil is still everywhere.

Cliff

 

image.thumb.png.af0df5f3e12f6cc78644daea7ef53e2f.png

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Where can I find some large Adel clamps to get the scat ducts secured properly?  I'm going to obsess about this now...

Cliff

 

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Cliff, don't take it personally- this is what we do when someone posts pictures of their engine installation.

I will add that the clamp holding the scat tubing to the intake tube might be a cause for concern and perhaps should be clamped using different means.  You can ask your mechanic to use actual Adel clamps instead, that would be a more appropriate method.

Try Aircraft Spruce for your aviation needs:

https://www.aircraftspruce.com/catalog/appages/ms21919clamps.php

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12 minutes ago, Andy95W said:

Cliff, don't take it personally- this is what we do when someone posts pictures of their engine installation.

I will add that the clamp holding the scat tubing to the intake tube might be a cause for concern and perhaps should be clamped using different means.  You can ask your mechanic to use actual Adel clamps instead, that would be a more appropriate method.

Try Aircraft Spruce for your aviation needs:

https://www.aircraftspruce.com/catalog/appages/ms21919clamps.php

Thanks, Andy...I'm only a little self-conscious about the setup under the cowl...I know it needs some attention and I'm more interested in getting advice than I am worried about looking like I don't know what I'm doing (because that part is true).

I found the part #'s in the M20J parts catalog just now...looks like a couple of MS21919DG26 and -34.  I'll get a few smaller ones for the JPI wires.  I'll slowly get this mess sorted out.

Cliff

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Regarding the fuel flow transducer: I heard that cleaning it sometimes fixes it and tried that. Tried running some carb cleaner spray through it and that didn't help so I took it off and soaked it in Hoppes. That made it better, but it was still intermittent. The transducer is made by Floscan which was purchased by JPI a year or so ago. I bought a new transducer and that fixed it though I'm still puzzled that the K-factor setting on the Shadin had to be tweaked so much to get the right flow indication. At the time, it was cheaper to buy the transducer from JPI than Spruce, so check both prices.

Regarding the tubing: I changed all mine to SCEET and got the SCAT out. The SCEET is double walled and much stiffer. Guy Ginby at GeeBee Aero N77GB@msn.com will make them if you send him the diameter and length. If you need a sharp bend NOT near the exhaust, you can get some short lengths of large diameter heat shrink tubing on eBay to shrink over it to hold a bend.

Skip

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26 minutes ago, FlyBoyM20J said:

Thanks, Andy...I'm only a little self-conscious about the setup under the cowl...I know it needs some attention and I'm more interested in getting advice than I am worried about looking like I don't know what I'm doing (because that part is true).

I found the part #'s in the M20J parts catalog just now...looks like a couple of MS21919DG26 and -34.  I'll get a few smaller ones for the JPI wires.  I'll slowly get this mess sorted out.

Cliff

Yeah, sorry about all the peanut gallery comments, but sometimes we just don't know when to stop :) 

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4 minutes ago, PT20J said:

Regarding the fuel flow transducer: I heard that cleaning it sometimes fixes it and tried that. Tried running some carb cleaner spray through it and that didn't help so I took it off and soaked it in Hoppes. That made it better, but it was still intermittent. The transducer is made by Floscan which was purchased by JPI a year or so ago. I bought a new transducer and that fixed it though I'm still puzzled that the K-factor setting on the Shadin had to be tweaked so much to get the right flow indication. At the time, it was cheaper to buy the transducer from JPI than Spruce, so check both prices.

Regarding the tubing: I changed all mine to SCEET and got the SCAT out. The SCEET is double walled and much stiffer. Guy Ginby at GeeBee Aero N77GB@msn.com will make them if you send him the diameter and length. If you need a sharp bend NOT near the exhaust, you can get some short lengths of large diameter heat shrink tubing on eBay to shrink over it to hold a bend.

Skip

Thanks, Skip - I've read about soaking in Hoppes in other threads (e.g., "Hoppes comes in a plastic bottle...so no worries about your plastic impeller"), but I'm not sure which Hoppes product to get at this point. 

Cliff

 

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