Fuel pump or circuit breaker?

Discussion in 'Maintenance Bay' started by DesertNomad, Jul 16, 2018.

  1. DesertNomad

    DesertNomad Pattern Altitude

    Joined:
    Jul 5, 2013
    Messages:
    1,851
    Location:
    Northern NV
    Display Name:

    Display name:
    DesertNomad
    I had not flown in six weeks, but today I went out to do several approaches under the hood in my Piper Dakota.

    After turning the master on, I turned on the fuel pump switch but nothing happened. I checked that the breaker was not tripped and cycled the switch a couple times. No joy. I figured that perhaps the battery was dead so I tried starting it. It started immediately.

    So I taxied it over to our maintenance hangar on the other side of the airport and shut down. I left the master on and tried the fuel pump again - same result. I then cycled the breaker twice and tried again. It worked. I cycled the switch once more and the fuel pump properly turned off and back on.

    So I went out and flew. During the course of the flight, I probably had the fuel pump on/off six times. Each time the fuel pressure responded showing the pump was working. After shutting down and getting fuel it worked fine as well.

    It did sit for six weeks but could be a bad breaker, a loose wire, minor corrosion on the breaker (through the breakers are all new (Klixon 7277) from last October.

    Any ideas?
     
  2. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    6,132
    Display Name:

    Display name:
    Dan Thomas
    Loose connection or a bad pump switch. Any inductive load (like a motor or solenoid) generates a voltage spike when it is shut off, causing arcing at the switch contacts as they open, and after thousands of operations they burn enough that they get intermittent. DC is far worse than AC that way, and switch ratings reflect that.

    Or the pump motor's brushes and commutator are worn out. How old/how many hours on that pump?
     
  3. James331

    James331 Ejection Handle Pulled

    Joined:
    Apr 18, 2014
    Messages:
    20,311
    Display Name:

    Display name:
    James331
    Do you have voltage at the pump?
     
  4. DesertNomad

    DesertNomad Pattern Altitude

    Joined:
    Jul 5, 2013
    Messages:
    1,851
    Location:
    Northern NV
    Display Name:

    Display name:
    DesertNomad
    Yes - it started working again and cycled correctly about 8 times today after initially doing nothing. Really not sure if it it the switch, breaker or pump. A local mechanic also suggested that it could be that it stopped in such a position with the winding that it could not start without a bit of "Jostling" which it would have had from taxiing across the field.

    Big mystery.
     
  5. Raymo

    Raymo Pre-takeoff checklist

    Joined:
    May 29, 2018
    Messages:
    361
    Location:
    Richmond Hill
    Display Name:

    Display name:
    Raymo
    My vote goes to the breaker, since the pump started working after you cycled it.
     
  6. DesertNomad

    DesertNomad Pattern Altitude

    Joined:
    Jul 5, 2013
    Messages:
    1,851
    Location:
    Northern NV
    Display Name:

    Display name:
    DesertNomad
    I think 800 hours on the pump... same as engine. Are they replaced at overhaul? A brief flip through the logs didn't show anything back to the overhaul in 2005.
     
  7. dmspilot

    dmspilot En-Route

    Joined:
    Oct 20, 2006
    Messages:
    3,736
    Display Name:

    Display name:
    Display name:
    No need to pay attention to switch ratings. Just use AC switches like Cessna did for 20 years. They are cheap, so when they melt inside they can just be replaced for little cost.

    --Disgruntled Cessna owner
     
  8. Brad Smith

    Brad Smith Line Up and Wait

    Joined:
    Nov 26, 2017
    Messages:
    724
    Display Name:

    Display name:
    Brad Smith
    No offense to anybody, but I’d ground it until a licensed A&P mechanic familiar with the plane has a look at it. He’ll be able to tell you a lot more than all the “armchair mechanics” on POA. Like I said, no offense.
     
    Paulie likes this.
  9. Plano Pilot

    Plano Pilot Pre-takeoff checklist

    Joined:
    Oct 24, 2016
    Messages:
    335
    Location:
    KADS
    Display Name:

    Display name:
    Plano Pilot
    Like the mechanic I have seen it happen before. When it does it again tap the pump with a hammer/tool and see if it starts running.
     
  10. DesertNomad

    DesertNomad Pattern Altitude

    Joined:
    Jul 5, 2013
    Messages:
    1,851
    Location:
    Northern NV
    Display Name:

    Display name:
    DesertNomad
    It's hard to give it over to a mechanic when everything is working.
     
  11. weirdjim

    weirdjim Ejection Handle Pulled

    Joined:
    Jul 8, 2008
    Messages:
    3,978
    Location:
    Grass Valley, CA (KGOO)
    Display Name:

    Display name:
    weirdjim
    We licensed A&P mechanics familiar with the plane send our kids to college on intermittents.

    You will search for HOURS and not find anything. Next time it happens, take a spray bottle of "plastic friendly" contact cleaner and squirt (in order) the switch (most probable) and then the breaker. Then get out to the pump and squirt the connections. Try the pump in between each of these operations and when the sucker kicks in, you've PROBABLY found the culprit. Next time it happens make that last one the FIRST one and if it kicks off right away you've found the problem. Like somebody else said, Cessna electrical engineers (that rank right up there in my opinion with used car salesmen and preachers) that would use an AC rated switch on a DC fairly high current circuit should be taken out and horsewhipped.

    Jim
     
  12. Brad Smith

    Brad Smith Line Up and Wait

    Joined:
    Nov 26, 2017
    Messages:
    724
    Display Name:

    Display name:
    Brad Smith
    My apologies, my position is that loss of the pump at a critical time or an electrical fire in the air (which I’ve experienced) is reason enough to have an experienced eye look at the problem rather than an inexperienced pilot/owner. They will have much better luck at locating the problem even if it’s not currently acting up. Just my 2 cents.
     
  13. Paulie

    Paulie Line Up and Wait

    Joined:
    Aug 21, 2014
    Messages:
    751
    Location:
    Naples fl
    Display Name:

    Display name:
    paulie
    Seems like you knocked off a little corrosion by cycling the switch/cb. Use some electrical contact cleaner. I am a a&p.
     
  14. DesertNomad

    DesertNomad Pattern Altitude

    Joined:
    Jul 5, 2013
    Messages:
    1,851
    Location:
    Northern NV
    Display Name:

    Display name:
    DesertNomad
    Did it again today. Tapping the pump fixed it... for now. New pump on order and grounded till Tuesday.
     
  15. NordicDave

    NordicDave Cleared for Takeoff

    Joined:
    Oct 31, 2015
    Messages:
    1,362
    Location:
    San Jose
    Display Name:

    Display name:
    NordicDave
    Good you isolated the problem. Have a look at CJ Aviation fuel pumps.

    AJ is a direct PMA replacement for Weldon or Dukes. They have a longer warranty and they're brand new pumps are not much more than rebuild Dukes. Mx I know well say to stay away from Weldon.

    I just put a CJ in my plane and worked great. Also check your service manual for the proper pump. Not too shocking how many old planes have the WRONG pump, because that's what the FBO had on the shelf to get a going. CJ will take non-similar pumps as cores.
     
    Last edited: Aug 17, 2018
  16. Jeff Cutler

    Jeff Cutler Pre-takeoff checklist

    Joined:
    Apr 9, 2005
    Messages:
    152
    Display Name:

    Display name:
    Jeff
    New for me was north of $4k so I searched around for rebuild shops. Aeromotors overhaul $800.00, and you get the original back if you can wait about a week for turnaround.
     
  17. DesertNomad

    DesertNomad Pattern Altitude

    Joined:
    Jul 5, 2013
    Messages:
    1,851
    Location:
    Northern NV
    Display Name:

    Display name:
    DesertNomad
  18. Dan Thomas

    Dan Thomas Final Approach

    Joined:
    Jun 16, 2008
    Messages:
    6,132
    Display Name:

    Display name:
    Dan Thomas
    He likely has a vane pump, not a solenoid pump. Vastly different, and the pressures are much higher. Injected engine need those pressures to keep the engine running if the engine-driven pump quits. A carbed engine only needs 4 or 5 psi.
     
    Jeff Cutler likes this.
  19. Jeff Cutler

    Jeff Cutler Pre-takeoff checklist

    Joined:
    Apr 9, 2005
    Messages:
    152
    Display Name:

    Display name:
    Jeff
    Yep —
     

    Attached Files:

  20. NordicDave

    NordicDave Cleared for Takeoff

    Joined:
    Oct 31, 2015
    Messages:
    1,362
    Location:
    San Jose
    Display Name:

    Display name:
    NordicDave
    Brand new PMA CJ Aviation electric pumps are about $1300ish.