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Fuel Vapor - low fuel pressure

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Yesterday I changed the brake pads on my CTLS.  After completing multiple high speed taxi's for brake scrub in, I taxied back to the hanger to drop off the A&P, shut down, settled up and performed the starting checklist.  Engine was shut down 10-15 minutes.  after engine start, I proceeded to the before take off checklist.  and immediately began to get a Low Fuel Pressure alarm.  After subsequent shut down and re-start, then continued run-up, it eventually cleared.

It is the A&P's belief, and mine as well, that the fuel in the fuel lines inside the engine cowling was vaporizing due to the higher engine temps when shut down; beginning or partial vapor lock. I was running 93 Octane - 10% ethanol auto fuel.  I'm in Florida and it was maybe 82 degrees outside.  However, I'm told that winter blend fuels with lower vapor pressures are distributed in Florida also because they are cheaper to produce.

I've never experienced an issue with this before.  Likely this is because I have never attempted to take off shortly after activities that would cause higher temperatures to form under the cowling.  It got my attention.  I flew to Seabring and added 10 gallons of UL94 to the wings to blend and increase the Vapor Pressure of the Mogas that I still had onboard.

I really wish more airports would start carrying an aviation fuel that was unleaded.

Just thought I would share.

Gary

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"Engine was shut down 10-15 minutes.  after engine start, I proceeded to the before take off checklist.  and immediately began to get a Low Fuel Pressure alarm.  After subsequent shut down and re-start, then continued run-up, it eventually cleared."

 

This can be very normal and I have seen and heard of it hundreds of times. It usually clears as you taxi and get some cooler fuel up in the lines. When the planes sits after flying hoses can heat soak and there is no way for cooler fuel to get up into those hotter lines without circulating more fuel usually by starting the engine. I have never seen an engine quit because of this in a CT.

We fly out here when it's over 100F. This happens and usually isn't an issue. The carbs can run on a lot lower fuel pressure than the advertised 2.2 psi and where the alarm is set. I know I tested it.

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Roger-

Thanks for your reply.  The A&P I was working with had the same input.  He is very experienced w CT’s as well and echoed that he had seen it drop to alarm before but had never had one quit.  He also flies CT’s. And has for a very long time.

I trust what he tells me and also very much appreciate your input on all things CT.

Gary

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Gary,

I had similar experience while waiting/idling about 10 minutes after run-up prior to departure from a Florida airport last week.  I got the low fuel pressure warning about 50 feet above the runway.  By the time I was at 300 feet it went away.  I had about 35 hours on my new fuel pump (5 yr change) and was immediately concerned there could be an issue with the new pump.  I flew the plane about 8 hours the next two days and the issue never re-surfaced.  There was never any issue of decreased performance but it certainly got my attention.  Glad to hear this isn't uncommon as it had been moved to the front of my instrument scan the entire trip home.

thx

todd

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The low fuel pressure alarm goes off at 2.2 psi. The engine will run just fine at lower pressures. It will run even if the fuel pump quits (high wing head pressure) at about 5K rpm, but not full throttle. A fuel pressure sender can go bad or become clogged which will also lead to a low pressure alarm. Yes vapor can form after the engine is run and then turned off and as it sits the hoses heat soak. This should go away after the engine restart and running it at higher rpms to get cooler fuel back into the hoses.

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Unless you have a fuel injected engine.  Fuel pump quits in a CTLSi - engine quits - unless second fuel pump is on.

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Gary

 

Same as you... 93 w/10% ethanol 

Flown 3 more times back here in the cold and issue has never re-appeared.

 

Todd

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