Thorp Air Command - T18.net

I think my mechanical fuel pump may be talking to me, but I'm not sure.......
My fuel pressure readings on a couple of flights would show in the 5-7 psi range for a couple minutes, then go back down to about normal.

So, I bought a new sender and visually checked and tugged on the ground wire from the sender (at both ends of the ground wire). Then I went flying and I was seeing the same fuel pressure of 5-7 psi range for a few minutes during flight, then back down to normal range.

Prior to one flight, I saw the 5-7psi range show right after start up while I was still sitting in front of my hangar.

Last flight, I was seeing more normal readings, but fuel pressure dipped to 1.5psi at one point. I turned on my electric fuel boost pump, which moved the fuel pressure up to about 3 or 4 psi, but after I turned the electric fuel boost pump off, fuel pressure dropped a little, but not back down to 1.5 psi.

I now am beginning to doubt an electrical/sender issue. Should I get that new fuel pump on order now, or am I missing something else?

Not sure what you mean by normal ? I have the mechanical pump and a boost pump and I get around 4-6 psi with boost pump on or off . You can tell the boost pump is working as I turn it on prior to engine start and I see about 5 psi . After T/O I turn the boost pump off and I still see around 5-6 psi on the fuel pressure gauge . EAA web site has a good write up by Tony B. with respect to basic fuel systems including mechanical/boost pump operation . RU seeing any fuel leaking out the "weep hole" on the mech pump ?

RB
The Man With The STAR

my normal psi seems to be in the 3-4psi range. Seeing 5-7 psi, and 1.5 psi are both definitely a change from what I have always seen for psi.

Now that you mention it, I cant recall seeing my electric boost pump make a difference like it has recently....especially when fuel pressure dipped to 1.5psi, I turned on the electric fuel boost pump, and the fuel pressure went up to 3 or 4 psi......hmmm

I see no fuel leaking from the weep hole on the mechanical fuel pump.

Am I seeing gremlins that aren't really there......kinda like that immediate roughness you feel in the engine once out over open water?

Don't go over open water !

RB

Check for diluted oil. One failure mode dumps fuel into the sump via the accessory case.

_________________
Bob Highley
N711SH
SN 835
KLAL

do you have a check valve in your system ? it may be not sealing at times. does your elect. pump have a screen built into the pump ? hint, if it is a round body elect. style pump the bottom cap may be removable and house a screen type filter. I have found many of these not looked at in many years and causing issues.
Phil
118BC

I'll check for diluted oil. I learned something there.

no check valve. My electric fuel boost pump does have a screen, which I just checked during the CI in October. It was clean.

What bothers me is that the fuel pressure was reading both high and low. If it was an electrical issue with a ground or sender, I would have thought the indication would have only gone either high or low.

Go to Vans Airforce site, there is a string on fuel pumps doing exactly the same, maybe you can find an answer

Bill is right . A butt load of very interesting articles on fuel pumps (electric/mechanical) . The care and feeding of the beast .

RB

found it. thanks for the tips.

What was causing your problem???
Phil

Phil, I just meant I found the thread over on VAF.....I haven't been back out to the airplane to look at my possible problem yet.

the culprit was a poor ground....sheesh, grounds can be frustrating.

Why are you running a fuel pump? John Thorp told me that a fuel pump can't fail if it is not installed. Gravity never fails.

Gary Green

I'll second that.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE