low fuel pressure

Tom-D

Tom-D

Taxi to Parking
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Feb 23, 2005
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Tom-D


  • PA 28-140 less than 100 hours since major overhaul. new accessories at overhaul.
    symptoms mixture closed, throttle closed, master switch on, fuel pump switch on, electric fuel pump runs quickly for bout 10 seconds then slows to 1 click per second. runs that way for about 30 seconds then slows to 1 click every 30-40 seconds.
    After start and warm up, going to full throttle, the fuel pressure will drop from the middle of the gauge to near the bottom of the gauge (not at the bottom) engine continues to run normally.
    no leaks found either in the fuel system or the primer lines, primer pump works normally.
    This was discovered during departure climb, flight terminated, returned to the airport normally, as soon as power was reduced the fuel pressure returns to the middle of the gauge.
 
Are you sure no one put E-10 auto fuel in it? Wouldn't be the first time E-10 caused aircraft fuel lines to swell internally and restrict flow.
 
Capt. Geoffrey Thorpe said:
Are you sure no one put E-10 auto fuel in it? Wouldn't be the first time E-10 caused aircraft fuel lines to swell internally and restrict flow.
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I have no idea what fuel has been in it, but it doesn't have an auto fuel STC.
 
What does it do on the ground without fuel pump on? My PA28-181 has pump on to start. Pump comes off during warm up. Pump goes back on for takeoff. Mine tends to hang out at the white line or lower. Never seen it in the red.
 
Not sure about that plane, but most planes with an electric fuel pump also have an engine-driven pump. There are often check-valves. I had a similar problem in the Commander and it turned out to be a bad electric pump apparently due to a bad internal check-valve.

May be different on that plane/engine.
 
Where is the bottom of the green arc on the gauge? I seem to recall it being something like 0.5 psi. I wouldn't necessarily assume that anything is wrong if it is within the acceptable range, but certainly worth investigating.

The local flight school has an Archer that does pretty much what you describe. It seems to be fine, or at least nobody has found a problem with it when investigated.
 
Two fuel tanks? Does each have a vent? Is the fuel pressure different on one vs the other?
 
Any power setting below full power the gauge stays in the middle of the green, no real pressure readings just the green with a area each side of that.
I think we found the problem..
the fuel selector wasn't fully in the detent. the owner ran it up, but had not touched the selector after the flight when he discovered it. and showed me the discrepancy. When I asked him what it did on the other tank he switched and could not duplicate the discrepancy.
I had him switch back, and he could not duplicate it on the either tank.
You can push the selector a little off the detent, and duplicate it on either.
new selector will be on order Monday.
 
Tom-D said:
Any power setting below full power the gauge stays in the middle of the green, no real pressure readings just the green with a area each side of that.
I think we found the problem..
the fuel selector wasn't fully in the detent. the owner ran it up, but had not touched the selector after the flight when he discovered it. and showed me the discrepancy. When I asked him what it did on the other tank he switched and could not duplicate the discrepancy.
I had him switch back, and he could not duplicate it on the either tank.
You can push the selector a little off the detent, and duplicate it on either.
new selector will be on order Monday.
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crap falls onto the FS in the Cardinal series and the plate with the machined divots gets full of crap and the the feel of the detents gets weak.

Or the plate could be worn out with a groove worn between the detent divots.



This one has around 4500 hours on it, detents are still firm and sharp fafter cleaning the gunk off it.
 
How many gpm is the engine pulling the at WOT/climb power vs. cruise? I know with my O540 take off power drops the fuel pressure way down to just above the bottom of the green even with the boost pumps on, but as long as it's >.5 psi it's per book. Comes right back up to 6lbs at first throttle reduction. Gets your attention the first few times.
 
bnt83 said:
crap falls onto the FS in the Cardinal series and the plate with the machined divots gets full of crap and the the feel of the detents gets weak.

Or the plate could be worn out with a groove worn between the detent divots.



This one has around 4500 hours on it, detents are still firm and sharp fafter cleaning the gunk off it.
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That is DISGUSTING
 
sferguson524 said:
That is DISGUSTING
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Appears to be old enough to shave.

It's just dust and lint and old fuel or oil scum. Disgusting is mouse poop or dead mice. Or a thick layer of bird poop. Or puke. Puke stinks for a long time.
 
I don't have a single customer that has that much dirt in the entire aircraft.
 
Checkout_my_Six said:
did you check the fuel lines.....for a collapsed/clogged hose?
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the new teflon hoses this aircraft has will not collapse with the pressures in this system.
besides it is fixed. works great, lasts a long time now.
 
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