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high fuel pressure

nedricher

Well Known Member
I am running an O-320. The type certificate data sheet specs the fuel pressure at .5 psi to 8 psi. It has always been in that range. Last flight it went up to 10.5 psi. Any ideas what would cause that other than a pressure sending unit. The pressure was with the engine driven pump only. With the electric pump turned on it went even higher, like around 12 psi.
 
I am running an O-320. The type certificate data sheet specs the fuel pressure at .5 psi to 8 psi. It has always been in that range. Last flight it went up to 10.5 psi. Any ideas what would cause that other than a pressure sending unit. The pressure was with the engine driven pump only. With the electric pump turned on it went even higher, like around 12 psi.

A bit of extra circuit resistance.
 
These pumps use spring pressure on the diagram to build pressure, the engine just “re-cocks” the pump. Springs don’t get stronger with age so I don’t know it can build more than design pressure. I have been told excess crank case pressure can cause an increase, and that makes sense, but I would test your pressure gauge first. If it’s a single wire design the ground path needs to be looked at, I’ve seen them mounted in an anodized fitting and that can cause problems.
Tim Andres
 
Gauge or wire problem is the 99.9% probability. Start by checking it with a know good analog gauge.
 
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