BruceMe
Well Known Member
I have two problems, and they are likely related.
Background: RV4, IO-320, 160HP, C/S Prop, all fuel line is fire sleeved, but the mechanical pump is exposed.
My engine baffling is marginal. I can't sustain a max power climb for more than two minutes without overheating concerns. Even a 75% cruise climb at 110kias will generate CHTs in the 410 range. In the 110F typical summer temps in KC area, cruise CHTs can edge into 400 at power settings over 60%.
Second/new problem: Mechanical fuel pump losing pressure in cruise. The mechanical fuel pump always "fluctuated" it cycles from 20-25psi on about a 0.5hz cycle. About 18mo ago on a cross country the range of fluctuation dropped lower until the engine started to sag (12psi), I flipped on the electric and "limped home". The pump was old, I figured it was warn out, so I replaced it. Now I have a new Tempest AF15473 installed and it's been running for over a year, still fluctuates, but never dropped below 18psi.
Well yesterday was 100F on the ground, not much cooler at 4,500' and the mechanical pump fluctuations dropped below 15psi again. I turned on the electrical boost and it went away. I left it on for a while, turned it off and the sensors showed the mechanical did ok for about a minute, then started fluctuating and dropping again.
I see a couple different options, I wanted to know if anyone on here has seen this and how they solved it?
1 - Cool the engine better (drop the CHTs)
2 - Shroud the fuel pump and give it it's own plenum air feed
3 - Get Lycoming fuel pump and see if that works better
What else? Thoughts?
Background: RV4, IO-320, 160HP, C/S Prop, all fuel line is fire sleeved, but the mechanical pump is exposed.
My engine baffling is marginal. I can't sustain a max power climb for more than two minutes without overheating concerns. Even a 75% cruise climb at 110kias will generate CHTs in the 410 range. In the 110F typical summer temps in KC area, cruise CHTs can edge into 400 at power settings over 60%.
Second/new problem: Mechanical fuel pump losing pressure in cruise. The mechanical fuel pump always "fluctuated" it cycles from 20-25psi on about a 0.5hz cycle. About 18mo ago on a cross country the range of fluctuation dropped lower until the engine started to sag (12psi), I flipped on the electric and "limped home". The pump was old, I figured it was warn out, so I replaced it. Now I have a new Tempest AF15473 installed and it's been running for over a year, still fluctuates, but never dropped below 18psi.
Well yesterday was 100F on the ground, not much cooler at 4,500' and the mechanical pump fluctuations dropped below 15psi again. I turned on the electrical boost and it went away. I left it on for a while, turned it off and the sensors showed the mechanical did ok for about a minute, then started fluctuating and dropping again.
I see a couple different options, I wanted to know if anyone on here has seen this and how they solved it?
1 - Cool the engine better (drop the CHTs)
2 - Shroud the fuel pump and give it it's own plenum air feed
3 - Get Lycoming fuel pump and see if that works better
What else? Thoughts?