Low Fuel Pressure immediately after startup

RhinoDrvr · #1 10-22-2018, 12:12 AM

Did a search here, but couldn’t find any posts with my specific issue;

My RV-8 has Airflow Performance fuel injection fitted to a Lycoming O-360-A1A and an Electronic International fuel computer that had fuel pressure reading and dual PMAG’s.

On engine start (cold), after priming with the electric boost pump, I’ll start the engine and the fuel pressure will be 10-12psi, tripping the red warning light. As the engine idles (around 800rpm) and I lean the mixture for taxi, the pressure will slowly start to build, until about 2 minutes after start it is at 23psi where it stabilizes.

The electric boost pump will bring the pressure up to 27psi immediately, but turning it off, pressure will drop again to where it was before.

Fuel pressure in flight seems normal; during climb it’ll hover between 22-23psi normally, then stay around 23-24psi in level cruise and descent.

Every once in a rare while (1 or 2 times per 100 hours) the pressure will drop down to 18psi or so in flight, then recover typically within 1 minute without the boost pump. The engine has always run fine.

Is this normal post-start behavior? The engine will not run well below 5psi on a hot start, but that seems like normal vapor lock; in addition, the pressure reads what I would expect during all phases of flight and reacts to the boost pump, so it doesn’t seem like an indication issue.

Thoughts? I recently cleaned all the fuel filters during annual and found no debris in them. All the fuel fittings I touched seemed tight, although I admittedly did not check every one in the system. I haven’t found any blue stains anywhere.

DanH · #2 10-22-2018, 07:08 AM

Evan, how old is that pump? Some recent dismantling of Lycoming pumps suggests they have an age limit.

RhinoDrvr · #3 10-22-2018, 10:44 AM

I?ll have to look in the logbooks to be certain, but around 600 hours or so.

Kyle Boatright · #4 10-22-2018, 10:58 AM

Quote:

Originally Posted by RhinoDrvr

I?ll have to look in the logbooks to be certain, but around 600 hours or so.

Might want to consider calendar time too. Mine failed at around 15 years, 900 hours.

RhinoDrvr · #5 10-23-2018, 10:39 AM

Took a look at the engine logbook today. The fuel pump was installed in 2012 at 983 hours.

So the pump is 6 years / 327 hours old.

Carl Froehlich · #6 10-23-2018, 11:19 AM

I'd start looking for an air leak - perhaps on a component that gets warm after engine start. That might explain the difference between pressure at start vs running.

Don't overlook the fuel pressure sender or it's connections as a potential culprit. If you can, connect a test gauge to the same place the fuel pressure sender is connected and see how it compares.

Carl