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Heat and mechanical pump woes

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?
 
Thumb typing. Pardon the brevity

Standard responses are abundant regarding sealing baffling.

Re problem 2 What fuel are you burning?

I’d verify there’s no “new” pressure losses up to the MFP. May/may not be a vapor pressure issue but it doesn’t sound good based on the limited data.

Blast cooling will help (to the potential detriment of other components) but Don’t shroud the pump. It will heat up quickly on the ground and compromise it’s life.
 
I agree with Freemasm
-Baffling work is in your future
-& a 3/4" or 1" scat tube directed to the fuel pump housing might help you fuel pressure issue. Heat is the culprit. Also look & see if any heat shrouds on exhaust pipes runners near fuel lines might help.
 
Thanks everyone, I'll look into all those. I do already have a heat shroud on the exhaust, and I may have hoses running a bit closer. This wasn't an issue until after I did my overhaul... maybe I routed fuel lines a bit closer?
 
In my experience a small air leak on the suction side of the mechanical pump and downstream of the boost pump generated similar — although more severe —symptoms. Perhaps worth checking for any kind of minor, perhaps intermittent, air leak (fittings, hoses, filters, etc).

And do work on your baffling …

Peter
 
Fuel pump shroud

If you figure a good fuel pump shroud on RV4 …please post pictures …..very tight on room …so I ended up with just a blast tube pointing right at fuel pump ( tube pretty much touches pump ) held in place with adel clamp on firewall foot wells . Couldn’t figure a shroud the would fit ….bought commercial ones and ended up returning
 
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