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  #1  
Old 11-28-2020, 09:15 PM
Bsquared's Avatar
Bsquared Bsquared is offline
 
Join Date: Mar 2018
Location: California
Posts: 140
Default High Fuel pressure

I did my first flight today in my 14A (went great) but I am home this evening reviewing the data download from the first 2 flights. With the engine at idle and no boost pump my fuel pressure is steady around 35 PSI. When I turn on the boost it spikes up to 42-45 PSI. As soon as I go to full power for take-0ff the pressure drops down to the mid 30's and when I shut off the pump it drops to 30. the Lycoming manual says 45 PSI is the high limit for the fuel servo. Are these pressures typical?
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  #2  
Old 11-29-2020, 08:59 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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I believe that 25-30 PSI is considered a relatively normal range of operation with MOST mechanical pumps being closer to 25 (sometimes lower in cetain conditions) and the elec pumps in the middle to upper end of that range. Yours seem quite a bit higher than normal, but not outside of what the servo can handle. I would be looking for an instrumentation issue. Possibly you have the wrong calibration curve for your sensor EMS combination or possibly high resistance on the ground. Is the FP sensor style a transducer (i.e. three wire) or resistive (one or two wires)? A ground issue would be limited to the resistor style for your symptoms.

Larry
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Last edited by lr172 : 11-29-2020 at 09:43 AM.
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  #3  
Old 12-04-2020, 10:16 AM
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Bsquared Bsquared is offline
 
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As a follow up...I contacted Andair and they gave me a simple procedure to adjust the output pressure without removing the pump. I will do it this weekend and report on the results
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  #4  
Old 12-04-2020, 01:15 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Bsquared View Post
As a follow up...I contacted Andair and they gave me a simple procedure to adjust the output pressure without removing the pump. I will do it this weekend and report on the results
With the boost pump off, you are still getting 35 at idle and 30 at full power in the mechanical pump. That is a good bit high for the norm on a mech pump. I still suggest that you verify your FP sender/instrument.

Larry
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  #5  
Old 12-04-2020, 06:55 PM
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Bsquared Bsquared is offline
 
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Quote:
Originally Posted by lr172 View Post
With the boost pump off, you are still getting 35 at idle and 30 at full power in the mechanical pump. That is a good bit high for the norm on a mech pump. I still suggest that you verify your FP sender/instrument.

Larry
Swapped the oil and fuel senders (latest version Kavlico unit..... identical units with 0-150 pressure range) and had same readings. After speaking with Lycoming support I am not concerned with 30 psi cruise fuel pressure.
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  #6  
Old 10-29-2021, 01:02 PM
Bgill Bgill is offline
 
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Location: Douglas, GA
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Default High pressure readings as well

I am seeing the same high pressure as Bsquared. I had assumed that it was a calibration issue and would deal with it when I opened up the cowl. Well today I did.

With engine off and mechanical pump on. I am seeing 42 psi. I put a dial pressure gage on the extra port and both the same 42 psi. In reading the Andair spec, it looks like it should be 30-33 psi max - no flow. So I am now confident in the gage but need to resolve the actual pressure issue.

Bsquared, did you ever adjust the Andair pump to reduce the pressure? Results?
And could you send me a copy of the adjustment procedure?

Thanks,
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  #7  
Old 10-30-2021, 09:01 AM
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Bsquared Bsquared is offline
 
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Quote:
Originally Posted by Bgill View Post
I am seeing the same high pressure as Bsquared. I had assumed that it was a calibration issue and would deal with it when I opened up the cowl. Well today I did.

With engine off and mechanical pump on. I am seeing 42 psi. I put a dial pressure gage on the extra port and both the same 42 psi. In reading the Andair spec, it looks like it should be 30-33 psi max - no flow. So I am now confident in the gage but need to resolve the actual pressure issue.

Bsquared, did you ever adjust the Andair pump to reduce the pressure? Results?
And could you send me a copy of the adjustment procedure?

Thanks,
Yes, Andair sent me a procedure for adjusting the relief valve on the pump and I was able to lower it by about 5 PSI. I still see occasional fuel pressures around 45 PSI with the boost pump on and the engine at slow idle but it is much better than it was. I could not adjust the relief valve any lower because I was worried about thread engagement on the adjusting screw. Contact Andair for the procedure…..it is pretty simple.
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  #8  
Old 10-31-2021, 05:29 AM
design4p design4p is offline
 
Join Date: Jul 2018
Location: CORWEN
Posts: 64
Default High Fuel Pressure

Hi,

I had exactly the same problem.

Andair explained how to adjust the pressure but with only a single thread remaining on the adjuster with not much reduction in pressure.

The result was that Andair replaced the pump free of charge (great service).

They said the pressure sensor assembly needed re calibrating.

Hope this helps - Regards John (In the UK)
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  #9  
Old 10-31-2021, 04:42 PM
Bgill Bgill is offline
 
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Default Thanks for the info

Thanks for the info. I will call them tomorrow and see what they say.
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