just the other day I noticed after startup my fuel pressure gauge would fluctuate when it used to hold steady around 5 psi lycoming 0-360 after about 10 minutes in flight it stabilized at 4 and worked its way back to 5 psi. on the ground before start up you can hit the aux pump and no fluctuations goes between 5-8 . Called lycoming they Said its your fuel pump is starting to go. Eventually you will have to replace it. He said it shouldn't be a problem to fly it because of the aux and it will get worse. Has anybody have this problem before. I'm think I should replace it ASAP if this is the problem
Fuel pump going bad
- Thread starter Xcfire
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SoCal RV Flyer
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SoCal RV Flyer
How many hours on the pump? It could be a sender issue as well.
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Aztec Flyer
It pays not to jump to conclusions, and diagnose through investigation. The electric boost pump is usually in parallel with the engine driven pump, but it usually has a check valve on the downstream side so when it is off the engine driven pump isn't driving fuel backward through the boost pump to the suction side. If that check valve is not holding completely it may create the same symptom you describe. This is just one example of what might be happening. Suggest you go through the fuel system schematic for your airplane and identify every possible cause, then test for each to get an accurate diagnosis before starting to replace [expensive] parts.
comanche pilot
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Be aware that in some installations the new replacement pumps are larger than the original A.C. produced pumps and can cause contact between the pump body and motor mount. This was an issue on my Comanche and I purchased a rebuilt original style pump rather than modify the engine mount. There was room to install the later style pump, but upon start up and shut down the pump would strike the mount. Pretty common knowledge among the 0-360 powered Comanche owners, not sure if this applies to other aircraft. And yes, my observation of fuel pressure was identical to your circumstances. Rebuilt pump and steady fuel pressure along with heart rate continued. :0)