Fuel pressure numbers

[Atanyspeed]

Just wondering what other IO-390 builds are getting for fuel pressure in cruise. I’m seeing 18-19 psi. An other aircraft with a 390 was showing 29-30 psi non thunderbolt Engine is running fine with good fuel flow. The engine manuals I’ve read are not clear on the psi coming out of the fuel pump as is set up by Van’s.

[Av8rRob]

Originally Posted by Atanyspeed

Just wondering what other IO-390 builds are getting for fuel pressure in cruise. I’m seeing 18-19 psi. An other aircraft with a 390 was showing 29-30 psi non thunderbolt Engine is running fine with good fuel flow. The engine manuals I’ve read are not clear on the psi coming out of the fuel pump as is set up by Van’s.

Yeah that’s low. You should be getting 25-30 or so. I had to get a warranty replacement of my fuel pump at around 200 hours, so it does happen.

[Jetmart]

I am getting 26 - 28 PSI in a Thunderbolt 390 at 75% power.

[Navy76]

Your pressure seems low to me. I typically see 28-30 psi in cruise and around 32 with the boost pump on. FWIW, I’m running an Airflow Performance boost pump and the Aircraft Specialty filters in the wing roots and no filter in the center console.

[Atanyspeed]

Thanks for the inputs. I’ll be contacting Lycoming on Monday.

[AlexC]

Originally Posted by Atanyspeed

Just wondering what other IO-390 builds are getting for fuel pressure in cruise. I’m seeing 18-19 psi. An other aircraft with a 390 was showing 29-30 psi non thunderbolt Engine is running fine with good fuel flow. The engine manuals I’ve read are not clear on the psi coming out of the fuel pump as is set up by Van’s.

Also make sure your G3X (or other EFIS) is configured for the correct pressure sensor, and that the sensor's pressure range matches what is configured on the G3X (e.g. if the sensor's pressure range is 0-50psi, and the G3X is setup to use a 0-75psi sensor, your pressure would be off by 1.5x). I had that problem with one of my sensors, and a config change solved my problem.

_Alex

[N49ex]

Agree with other's numbers - I see 26 to 28 PSI. And agree, should check sensor/G3X correct data. BUT - my brand new Lycoming I/O-390's fuel pump leaked oil from the get go, and subsequently the replacement at 350 hours failed on take-off: watched the pressure drop and engine start to stumble, saved by the electric boost pump! So, yes these do fail, and sometimes at a remarkably young age!

Finally, you might also want to check your fuel routing and vulnerability to heat related vapor locking, as that can cause pressure drops as well.

Reinhard

[Bavafa]

Plus 1 for the configuration check, I had misconfigured mine and I was getting 18-19 PSI, changed the type of probe in the engine page and now the reading is correct.