Lost Fuel Pressure on Engine Driven Pump

[WileEcoyote75]

Last Sunday I went up for a short flight, OAT was 18F, Tanks were both half full and the engine is an O-360 with a gascolator. I use the booster pump to prime only and then shut it off immediately after startup. I was on the ground for at least ten minutes for run up and back taxi with no fuel pressure issues. The booster pump was started for takeoff. I was climbing out through 2000 agl with around 5psi of fuel pressure when I shut down the booster pump. The pressure immediately starting dropping off and was down around 0psi within 30 seconds, when I restarted the booster. The pressure climbed back to around 5psi. The engine ran perfect the entire flight. I stayed close to the airport and continued to climb, at around 6500 agl I shut down the booster pump again with the same results. On the third attempt the pressure stayed at around 3.5psi using only the engine driven pump. Will the engine driven pumps start to act up before failure? Bad Pump? Fuel Pressure Sending Unit? Air in the system? Is a Vapor Lock possible when its that cold? Let me know what you guys think.

Chad

[rleffler]

Originally Posted by WileEcoyote75

Will the engine driven pumps start to act up before failure? Bad Pump? Fuel Pressure Sending Unit? Air in the system? Is a Vapor Lock possible when its that cold? Let me know what you guys think.

Chad,

I had similiar issues on my first flight. Idle RPMs and everything was OK. The problem didn't show itself until WOT. In the case of the RV-10, I found previous incidents that were caused by either a bad pump or vapor lock.

The two of the people I talked with that experienced vapor lock, replaced their pump multiple times before installing a cooling shroud, which resolved the issue.

I probably should have taken a more scientific approach than I did to determine the exact root cause, but I wanted to complete Phase I before the weather started to become problematic. Lycoming replaced the fuel pump under warranty and I installed a cooling shroud at the same time. It was a PITA to uninstall and reinstall, so I didn't want to do it twice. My problem was solved, but unfortunately I don't know if vapor lock was an issue or was it simply a failed pump.

bob

[rvsxer]

I've had the same problem since day one, 1150 hours ago. I have an 0-360, MA4-5 carb with the enrichment kit and Lycoming factory pump. On mine it only happens at WOT, above 4,000 ft, with OAT below 25-30F. I have a Piper cooling shroud and 2" SCAT (with some restriction to cut the airflow) feeding it. As soon as I move the throttle off WOT the pressure recovers right away even with the electric pump off.

[Flyingleap]

Please look at Lycoming SB 548A. I had an odd loss of fuel pressure
from engine driven pump and this might have been it.....not sure....

[WileEcoyote75]

Lycoming SB548A does not apply to the O-360.

Thanks,
Chad

[Kyle Boatright]

Low *indicated* fuel pressure is a common issue. Use the search function on the site and search on "low fuel pressure" and you will find an abundance of discussion on the subject.

[Flyingleap]

Chad
SB548A is worded a little odd but:
"models affected are O-235 ; O290 ; O-340 ; (L)O and IO-320,
-360"

I have a O-360 A4M with a LW-15472 pump dated "4900" "must be replaced"

Yes, just a mandatory service bull.......
It may be why I lost fuel pressure and used the aux pump, just saying.

[rvsxer]

I should have made it clear in my earlier post that I am actually experiencing a partial power loss, not just low pressure indication. It is very predictable so I just turn on the boost pump during WOT operation at low OAT's. I built up my engine in 1999-2000 or so, and installed a new Lycoming pump. I'm going to check on that SB right away. Thanks for the heads-up.

[WileEcoyote75]

Thanks John,
I will investigate the service bulletin.

[Flyingleap]

Don't thank me. I was told about this a few weeks ago on "Doug's" site
after someone else had similar problems. Missed this SB, but will try very hard to not miss another one, and pass it on to others.

"Stay safe" and I mean it !