Kyle Boatright
Well Known Member
On the way out to the runup area today, I had a low fuel pressure warning. The digital gauge showed 0 or even slightly negative fuel pressure, but the engine continued to run. I turned on the electric fuel pump and the pressure came up to the normal operating range of 5-6 PSI. I turned the electric pump off, and the low pressure indication returned. Restarting the electric pump raised the pressure to normal again. I returned to the hangar, pulled the cowl, and looked for any obvious issues - blue fuel stains, etc. No joy.
The engine is a 160 HP, carbureted O-320 with an electric fuel pump and mechanical pump in series.
Here are the possibilities I've considered:
-Sender/gauge problem: Since the electric fuel pump raised the fuel pressure both times I turned it on, I'm going to assume the sender and gauge are not the problem.
- Intermittent failure of the low pressure mechanical fuel pump. Sam Buchanan had this problem once upon a time, but as far as I can tell, his posts didn't explain how he diagnosed it.
- Leaky fuel fitting or line, allowing air to enter the fuel system somewhere upstream of the mechanical pump (but after the electric pump?). Should I be able to test this (at least the connections between the electric pump and carb) just by turning on the electric pump with the engine shut down and looking for leaks and/or seeps?
- Collapsing fuel line. The fuel lines are stainless braided with a Teflon liner and should be good for a lifetime, but there are no guarantees in life.
This is a potentially dangerous problem and I'd rather identify and fix it with certainty before I fly again.
So I'd appreciate any thoughts people have on the subject. In the meantime, I'm going to dig through my Sacramento Sky Ranch book...
The engine is a 160 HP, carbureted O-320 with an electric fuel pump and mechanical pump in series.
Here are the possibilities I've considered:
-Sender/gauge problem: Since the electric fuel pump raised the fuel pressure both times I turned it on, I'm going to assume the sender and gauge are not the problem.
- Intermittent failure of the low pressure mechanical fuel pump. Sam Buchanan had this problem once upon a time, but as far as I can tell, his posts didn't explain how he diagnosed it.
- Leaky fuel fitting or line, allowing air to enter the fuel system somewhere upstream of the mechanical pump (but after the electric pump?). Should I be able to test this (at least the connections between the electric pump and carb) just by turning on the electric pump with the engine shut down and looking for leaks and/or seeps?
- Collapsing fuel line. The fuel lines are stainless braided with a Teflon liner and should be good for a lifetime, but there are no guarantees in life.
This is a potentially dangerous problem and I'd rather identify and fix it with certainty before I fly again.
So I'd appreciate any thoughts people have on the subject. In the meantime, I'm going to dig through my Sacramento Sky Ranch book...
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