Since it's a positive displacement pump, pumped volume should be very similar (at the same supply voltage) whether the engine consumes any fuel. Temp is obviously a variable. RV4 floors get hot; at least when powered by a Lyc. ;-)

On 5/22/2022 7:44 PM, Finn Lassen finn.lassen@verizon.net wrote:

Thanks Steve.

From your March/April 2017 posts it was a GSL392 that failed (high current draw/low pressure, even after you removed the insect you found in the inlet).

So this afternoon I ran the pump for about an hour. Amp draw from 3.04 to 2.86 depending on voltage. Pressure between 43 and 40 psi (also depending on voltage). No noticeable degradation. Of course the difference with this test is that no fuel went to engine -- all recirculated through pressure regulator and back to tank. But no signs of a failing pump in terms of higher current draw and less pressure.

I guess I should put a temp probe on the pump and see what it reads during flight to see if that could be a factor.

Finn

On 5/21/2022 9:01 PM, Stephen Izett stephen.izett@gmail.com wrote:

Hi Finn

I had from memory a 393 fail. Can’t recall the symptoms sorry.

I test before takeoff and then run both pumps below 2ooo ft incase of failure.

I plan to instal a comparator relay board in fuel pressure circuit to automatically bring on backup pump and failure indicator.

So testing before flight becomes - switch off and back on main engine pump. This will save amps and wear of backup pump.

When I switch off a pump at WOT the engine dies pretty much instantaneously and don't want to be fiddling with a restart in the Glasair which glides like a brick with the gear out in the breeze.

Regards  

Steve Izett

On 21 May 2022, at 10:30 pm, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:

Recently I noticed my fuel pressure being low. Noticed because engine did not come up in power when advancing to full throttle. Noticed mixture real lean. Checking fuel pressure as low as 28 psi (normally 35 and up to 40 at full throttle).

Going over my engine logs since first flight I now see that fuel pressure has been trending lower through each flight -- more pronounced on longer flights (40+ minutes). More and more pronounced over the months and became really noticeable over last month. Could explain why mixture tuning appeared to have changed. Nice to have engine logs from practically each flight.

But why? Pump getting weaker?

My primary fuel pump is a GSL414. I figured it was wasted energy to push way more fuel than needed through the pressure regulator back to the tank.

My secondary (backup) pump is a GSL393. When turning that on, fuel pressure comes back up to where it needs to be.

Anyone have experience with failing or weak EFI pumps, particularly the GSL414?

Finn

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