Finn,

It seems to me that the problem you’re seeing is consistent with the capacity of the pump not being sufficient for the max flow required by the engine and the pump flow capacity is decreasing with use.  You appear to have checked everything but the flow capacity of the pump under normal system pressure which is what you really need to know.  If you can divert the returning fuel flow from the pressure regulator to a measuring vessel and and collect that fuel for an accurately measured time, the pump flow rate can be calculated.  This flow rate should be greater than the maximum required by the engine by a comfortable amount.  

My apologies in advance if this is obvious.

Steve Boese 

On May 22, 2022, at 8:05 PM, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:



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Hi Finn

Thanks for the reminder of my pump issue. 

Yes, you chose more wisely the pump capacity. Mine were way overkill.

So I’m thinking options are:

1. Fuel Pressure transducer fault - No - as this was confirmed by the mixture monitor and tune going out.

2. Power supply to pump via fault in termination or switch current path - Unlikely, given the slow reduction - I would imagine a faulty connection would create a less uniform symptom.

3. Alternator Battery voltage/current reduction over time - No - You would see this in the log.

4. Significant Fuel leak - No - Would think this would have become obvious on inspection and not intermittent. 

5. Fuel Regulator - They are pretty simple but unsure if they can fail with this symptom?

6. Fuel filter blockage - Certainly this would have to be an obvious, but I take it you swapped this out.

7. Pump internal failure -

Electrical - ?

Mechanical breakage - ?

Flow Path - blockage - unlikely if filtered effectively

Where is your pressure transducer in relation to Reg/Any post pump filtering/Flow Transducer/Rail?

If fuel regulator and filters can be discounted, I’m struggling to trust the pump. But your test had it sounding in good shape and to spec.

So frustrating.

Cheers

Steve

On 23 May 2022, at 8:44 am, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.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 286 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