Mailing List flyrotary@lancaironline.net Message #67229
From: 12348ung@gmail.com <flyrotary@lancaironline.net>
Subject: RE: [FlyRotary] Re: Fuel pressure trending lower.
Date: Sun, 22 May 2022 09:08:56 +1000
To: 'Rotary motors in aircraft' <flyrotary@lancaironline.net>

Finn,

              Always the way with “diagnostics”.  You will not know until it is fixed.   If pressure is ok with both pumps going through the same filter? Then filters suggest are OK.   Main pump could be explained in that performance is marginal even when cold but when heated expands radially and efficiency drops just that fraction.

AS I said impossible to verify unless replaced.

Neil.  

 

From: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sunday, May 22, 2022 8:21 AM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Fuel pressure trending lower.

 

After maybe less than 75 hours in use?

Recently, during annual, I discovered I'd installed the pre-pumps filter the wrong way. Tried to clean the cartridge real well, but not impossible that some junk hidden under the edges could have gotten into the main pump input as I'm only running the backup pump for a few seconds during pre-flight checks. Actually that doesn't explain the long term decline. So back to the pump failing. Dang! But why full pressure when cold and then gradually dropping during flight (dropping more recently).

It's my understanding that the Walbro EFI pumps do not have check valves but acts as a valve when turned off. Thus no fuel off-valve in my RV-4.

Now I'm wondering if this is happening to others but just not visible when using the higher capacity GSL393, 392 or 391 pumps. They would have to degrade to below the fuel regulator setting before becoming noticeable.

For some reason the GSL393 is cheaper than the GSL414.

Finn
 
On 5/21/2022 5:58 PM, 12348ung@gmail.com wrote:

Finn,

            Once again the blind leading the blind, but it appears that wear and old age has gotten to your pump.  I suspect that as with the second pump all is normal, then that excludes filter and water etc, just needs a replacement pump IMHO.

                Easy when it is your money!

Neil.

            

 

From: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sunday, May 22, 2022 2:14 AM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: Fuel pressure trending lower.

 

Do EFI pumps have an internal check valve? Dirty fuel filter?  

 

Bobby


From: Rotary motors in aircraft <flyrotary@lancaironline.net> on behalf of Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net>
Sent: Saturday, May 21, 2022 9:30:30 AM
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: [FlyRotary] Fuel pressure trending lower.

 

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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