Bad Fuel Pressure gauge - please help

Datadriver

Datadriver

Line Up and Wait
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Datadriver
The fuel pressure gauge in our Arrow has big problems, as you can
see in this video:

http://www.youtube.com/watch?v=AJctupDS6kA

Details:
1) happens on either tank
2) only occurs with engine running (stable w/electric before start)
3) a fuel snubber fixed it for about 30 minutes, then it started again

Any ideas on how to fix this? The local A&P is out of ideas.:dunno:
 
One time I saw similar the fuel line was delaminating inside and a piece was flopping inside.
 
Datadriver said:
The fuel pressure gauge in our Arrow has big problems, as you can
see in this video:

http://www.youtube.com/watch?v=AJctupDS6kA

Details:
1) happens on either tank
2) only occurs with engine running (stable w/electric before start)
3) a fuel snubber fixed it for about 30 minutes, then it started again

Any ideas on how to fix this? The local A&P is out of ideas.:dunno:
Click to expand...

Ruptured Diapham in manual FP (anything blue ****ing out of the FP overflow line?. Does FP changing with altitude?
Crap in the spider/divider line going to the FP/FF gauge. BTW; what Arrow is this??
Bad gauge. You didn't mention if the engine was affected by this abnormality...if not a faulty gauge is a suspect.

Chris
 
It is a 1975 Arrow 2 with a Lyc io-360. Engine has about 100hrs on it after a factory overhaul to limits. Engine seems unaffected. Problem not related to altitude. Gauge dances faster the higher rpm.
 
Datadriver said:
It is a 1975 Arrow 2 with a Lyc io-360. Engine has about 100hrs on it after a factory overhaul to limits. Engine seems unaffected. Problem not related to altitude. Gauge dances faster the higher rpm.
Click to expand...

I watched the video and my guess is..................................................



It is that god awful music causing the needle to be erratic..:D:wink2:
 
Datadriver said:
It is a 1975 Arrow 2 with a Lyc io-360. Engine has about 100hrs on it after a factory overhaul to limits. Engine seems unaffected. Problem not related to altitude. Gauge dances faster the higher rpm.
Click to expand...

Where are you?
 
N801BH said:
I watched the video and my guess is..................................................



It is that god awful music causing the needle to be erratic..:D:wink2:
Click to expand...

Yeah, not my favorite tune. Xm radio channel 8
 
Datadriver said:
Gauge dances like that on ground during run-up. Video was shot at 3000msl.
Click to expand...

:rofl::rofl::rofl: in the country, airport. I always like solving interesting problems with machines. Just trying to figure if it could be practical to look at. If you don't want to make that public feel free to PM me.

Anyway, the suggestion to put another gauge on it is the quite appropriate next step thought I suspect it will show the same result, that looks like a sender side pulse.
 
Last edited:
Henning said:
:rofl::rofl::rofl: in the country, airport. I always like solving interesting problems with machines. Just trying to figure if it could be practical to look at. If you don't want to make that public feel free to PM me.

Anyway, the suggestion to put another gauge on it is the quite appropriate next step thought I suspect it will show the same result, that looks like a sender side pulse.
Click to expand...

The plane is based in Central Texas. I should add that originally we took it in for a steady low pressure reading...it would barely climb into the green by runup, and would no longer tick to the right when the electric pump was engaged. While troubleshooting that issue the electric fuel pump seized and was replaced. After that we got a good indication prior to start (jumps to middle of green arc and stays there). This is why we thought there was a bad pulse from the engine side or something as opposed to the gauge needing overhauling or something.

The electric pump was ancient and definitely needed to go. It seems like we have experienced some other failure with the gauge or engine sending side almost simultaneously.:mad2:
 
Datadriver said:
The plane is based in Central Texas. I should add that originally we took it in for a steady low pressure reading...it would barely climb into the green by runup, and would no longer tick to the right when the electric pump was engaged. While troubleshooting that issue the electric fuel pump seized and was replaced. After that we got a good indication prior to start (jumps to middle of green arc and stays there). This is why we thought there was a bad pulse from the engine side or something as opposed to the gauge needing overhauling or something.

The electric pump was ancient and definitely needed to go. It seems like we have experienced some other failure with the gauge or engine sending side almost simultaneously.:mad2:
Click to expand...

I'm looking more and more to a hose issue with that tidbit.
 
Air bubble or crap in the gauge line...?

Electric pump is a vane pump that puts up a good (non-pulsing) amount of pressure; even with a compressible bubble it doesn't "thump" the bubble like a surge pump. The engine driven diaphram pump will show a pulse when there is an air bubble in the line and it WILL change cadance with RPM.
At this point I'm with Henning (not in the literal sense :goofy:) ...burp the line at the gauge and see if the indication changes.
While you're on the gauge end look for any crap that may have been introduced during the engine swap and just now causing a problem.

Chris
 
Shop called today. They cleaned out the line from the engine pump to the gauge, ran it up and could not recreate the issue. They also said the line made a sharp turn and was almost kinked. They are going to make a longer line with a more gentle arc.

Lycoming told them sharp turns are a no-no.
 
I've seen something similar on direct reading gauges, and found bits of fuel lube in the line. With that cleaned out the problem went away.

It would be best to test it with a calibrated gauge to ensure that you're getting the fuel pressure you should. It would be a real tragedy to have a stable gauge reading and poor fuel flow. A blockage in some systems can create that, too, trapping pressure which reads as good, but isn't.
 
Datadriver said:
Shop called today. They cleaned out the line from the engine pump to the gauge, ran it up and could not recreate the issue. They also said the line made a sharp turn and was almost kinked. They are going to make a longer line with a more gentle arc.

Lycoming told them sharp turns are a no-no.
Click to expand...

Just for my own "need to know" archive; is this the same shop that put the motor in 100 hours ago?

The reason I ask is the gauge line doesn't come from the fuel pump to the gauge it comes from the fuel spider/divider on top of the motor...and that's a damn near straight shot from the divider thru the baffling to the firewall (as assembled by Piper) fitting.


Chris
 
Hiperbiper said:
Just for my own "need to know" archive; is this the same shop that put the motor in 100 hours ago?

The reason I ask is the gauge line doesn't come from the fuel pump to the gauge it comes from the fuel spider/divider on top of the motor...and that's a damn near straight shot from the divider thru the baffling to the firewall (as assembled by Piper) fitting.


Chris
Click to expand...

Different shop. I did a test flight with mechanic and all was well, then after the hot start problem reoccured :mad2:

Taxied back to shop. They cleaned some debris out of gascolator and finger screen. Run up was ok as was flight home. Going back out today for another test.
 
Datadriver said:
Shop called today. They cleaned out the line from the engine pump to the gauge, ran it up and could not recreate the issue. They also said the line made a sharp turn and was almost kinked. They are going to make a longer line with a more gentle arc.

Lycoming told them sharp turns are a no-no.
Click to expand...


Lol, yeah, that one just looked like a hose problem, good they found it quick.
 
Update: it was fine for 5 hours then the problem came back with a vengeance today. :mad2:I'm going to recommend we do the calibrated gauge test next.
 
My guess would be the engine driven fuel pump has a bad valve in it and is allowing some back pressure to go back up the fuel line causing the pressure to fluctuate. Sounds like it is sticking only sometimes. Could drive you crazy among other things. Theres my 2cents worth.

Randy
 
Looks like the hairspring needs adjustment, or you have a broken jewel at the instrument. Is that a Rochester gauge?
Instruments technician here, 25 years experience.
:wink2:
 
Henning said:
Ok, so what part that was built wrong before that caused this condition again? What's shaking? This may come down to an Adell clamp.
Click to expand...

Shop B thought that one of Shop A's lines had too much of a turn and might possibly kink. Lycoming concurred. That line was replaced and lengthened so there was a gentle turn. Obviously they were guessing cuz that didn't fix it.

Shop A was the one that did the install of an overhauled engine.:idea:
 
WarriorPilot said:
Looks like the hairspring needs adjustment, or you have a broken jewel at the instrument. Is that a Rochester gauge?
Instruments technician here, 25 years experience.
:wink2:
Click to expand...

I'm not sure. I'd really like to see a calibrated test gauge say for sure if the pressure from engine is ok or not.
 
Vaflier said:
My guess would be the engine driven fuel pump has a bad valve in it and is allowing some back pressure to go back up the fuel line causing the pressure to fluctuate. Sounds like it is sticking only sometimes. Could drive you crazy among other things. Theres my 2cents worth.

Randy
Click to expand...

The engine pump was replaced at overhaul so that would be a shame - another thing to check...:rolleyes2:
 
Datadriver said:
The engine pump was replaced at overhaul so that would be a shame - another thing to check...:rolleyes2:
Click to expand...

Has it been disassembled and cleaned? These are simple as pumps and if there is a piece of crap stuck under a flopped valve you get this interesting stuff.
 
Datadriver said:
Shop B thought that one of Shop A's lines had too much of a turn and might possibly kink. Lycoming concurred. That line was replaced and lengthened so there was a gentle turn. Obviously they were guessing cuz that didn't fix it.

Shop A was the one that did the install of an overhauled engine.:idea:
Click to expand...

Jeez...... The "ol" blame game with the owner paying the admission fee.:yesnod::sad:....

It is either the gauge or the check valve in the fuel pump.... :idea:
 
Any updates/solutions to this thread?

I was reminded of this thread when I replaced a fuel pump on an IO-360 in a friends RV-8 a few weeks ago...procured a rebuilt pump from ACS (a Tempast rebuild).
Installed it with the lines going to the same ports (inboard from the electric pump and outboard to the fuel servo) and tried to start the motor. She refused to light off. No fuel pressure on the gauge. Even using the electric pump to prime the motor didn't work.
I unhooked the line coming from the electric pump to the manual pump input and turned the pump on...fuel went everywhere. Reattached the manual pump input line and removed the line going from the manual pump to the servo. Turned on the electric pump and nothing! Something inside this newly rebuilt pump was keeping fuel from going thru it.
Long story short; this "rebuilt" pump (complete with test card) had the entire bottom end of the pump on 180 degrees out so the check valve blocked the flow of fuel from the supply line.

After re-rebuilding the rebuilt pump everything worked great and everyone is happy...
I just include this to note that not all "rebuilt" pieces-parts are worth a ****e...don't dismiss the fuel pump because it was rebuilt...:yes:

Chris
 
Hiperbiper said:
Any updates/solutions to this thread?

I was reminded of this thread when I replaced a fuel pump on an IO-360 in a friends RV-8 a few weeks ago...procured a rebuilt pump from ACS (a Tempast rebuild).
Installed it with the lines going to the same ports (inboard from the electric pump and outboard to the fuel servo) and tried to start the motor. She refused to light off. No fuel pressure on the gauge. Even using the electric pump to prime the motor didn't work.
I unhooked the line coming from the electric pump to the manual pump input and turned the pump on...fuel went everywhere. Reattached the manual pump input line and removed the line going from the manual pump to the servo. Turned on the electric pump and nothing! Something inside this newly rebuilt pump was keeping fuel from going thru it.
Long story short; this "rebuilt" pump (complete with test card) had the entire bottom end of the pump on 180 degrees out so the check valve blocked the flow of fuel from the supply line.

After re-rebuilding the rebuilt pump everything worked great and everyone is happy...
I just include this to note that not all "rebuilt" pieces-parts are worth a ****e...don't dismiss the fuel pump because it was rebuilt...:yes:

Chris
Click to expand...

This case screams for someone to advise the FAA /FSDO of that failure... How can a yellow tagged fuel pump have a passing test card with that error during the rebuild /test phase..... :dunno::dunno:..
 
N801BH said:
This case screams for someone to advise the FAA /FSDO of that failure... How can a yellow tagged fuel pump have a passing test card with that error during the rebuild /test phase..... :dunno::dunno:..
Click to expand...

I thought the same thing. Then I had a second thought. Ever hear of Kelly Aerospace???:yikes:

Chris
 
N801BH said:
It is either the gauge or the check valve in the fuel pump.... :idea:
Click to expand...

Yep.
Either the gauge is right, or it's wrong. As another poster said, get a gauge directly on the engine and determine if the gauge is right or not.
Troubleshooting is much simpler after that.

I had an oil pressure problem. First question was "Is the gauge right?"
The answer was no, and that made fixing it easier.
 
While digging through ancient emails, I found the eventual resolution and wanted to post it here to close out this thread. In our case, the fuel bowl had been over tightened, which had damaged the assembly allowing air to bleed in. Prior to this, the gauge had been replaced, air blown through on the ground, adjusted the snubber, etc.
 
cool. I fly with mine behaving similarly, but the swing is not that wild. It's more of a high-frequency oscillation no larger than one needle width. Fast enough that the mean position of the reading is still "burn-captured" by your eye. No problems with the engine. Mine is probably an electric gremlin somewhere. No an uncommon thing with these indicators.
 
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