Question Fuel Pressure Fluctuation on mechanical fuel pump

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20 Feb 2024 08:56 #4219 by STEVE ELLS
Replied by STEVE ELLS on topic Fuel Pressure Fluctuation on mechanical fuel pump
Hi Robert,
Thanks for the update on the fuel tank vent line checks.

Have you flown it? 

Is the problem resolved?

Best,
Steve

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16 Feb 2024 11:58 #4214 by Robert Curry
Replied by Robert Curry on topic Fuel Pressure Fluctuation on mechanical fuel pump
Steve,

We tested the fuel tank vents and found one of the four was restricted. Checked the fuel lines and they are fine. Will be doing the pressure test soon. Thank you!

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27 Jan 2024 10:45 #4184 by STEVE ELLS
Replied by STEVE ELLS on topic Fuel Pressure Fluctuation on mechanical fuel pump
Hi Robert,
Have you made any progress on solving this issue??

Thanks,
Steve

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18 Jan 2024 18:21 #4182 by Robert Curry
Replied by Robert Curry on topic Fuel Pressure Fluctuation on mechanical fuel pump
Thank you Steve, it's a PA32-300 fuel injected.

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18 Jan 2024 10:45 #4181 by STEVE ELLS
Replied by STEVE ELLS on topic Fuel Pressure Fluctuation on mechanical fuel pump
Hi Robert;
I suggest you test the EI fuel pressure sender you got with your CGR 30. 
I don't know what model Piper you're flying, but the following test would be very simple to do on my Comanche because I mounted the fuel pressure sender on the firewall.

Disconnect the hose to the fuel pressure sender, or if it's screwed into a fitting, unscrew it. Leave the wiring attached. Rig up a test set up--probably wouldn't need more than a pipe union that your mechanic might have (or he could buy an expensive one at the local hardware store). Screw the sensor into one end of the union and a way to apply air pressure to the other end. Put an air pressure regulator in the "air in" end of the union.

Apply 3-5 psi if your engine is carbureted or and a pressure that's in the mid range of the fuel pressure limits of your engine if it's fuel injected. Then check the read out on the CGR 30. Turn on power to the CGR 30.
Is the FP reading solid? or does it jump around. If it jumps around, I'd get another sensor. 
If it does not jump around, I would look closely at the hose, if there's a hose connecting the sensor to the engine.

Since I don't yet know the model Piper you're flying, I'm doing a little guessing here, but if the FP is good with the boost pump on, that seems to indicate that the engine driven FP is glitchy or there's some kind of obstruction in the line. An obstruction could cause a higher than desired fuel pressure. I would temporarily plumb in what we call a direct reading fuel pressure gauge by "T" ing a fitting into the fuel pump "out" hose  so you can read the pressures the pump is producing when the engine is running. 

Let me know what you find.

Steve

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16 Jan 2024 16:43 #4178 by Robert Curry
New CGI 30 Combo installed January 2022.  Fuel pressure would fluctuate to yellow occasionally then in Feb 2023 would enter the red.  I had my A&P install a new Tempest mechanical fuel pump.  The fluctuations continued and after discussing with my A&P and reading an article on the electric boost pump check valve failures we installed an overhauled electric boost pump.  The fluctuations are continuing and have started to enter the red again occasionally.  The pressure is fine when the boost pump is on. Has anyone had similar problems?  Solutions? Thank you!

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