Fuel pump or circuit breaker?

DesertNomad

DesertNomad

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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?
 
DesertNomad said:
...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?
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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?
 
Do you have voltage at the pump?
 
James331 said:
Do you have voltage at the pump?
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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.
 
My vote goes to the breaker, since the pump started working after you cycled it.
 
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.
 
Dan Thomas said:
DC is far worse than AC that way, and switch ratings reflect that.
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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
 
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.
 
DesertNomad said:
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.
Click to expand...

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.
 
Brad Smith said:
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.
Click to expand...
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
 
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.
 
Seems like you knocked off a little corrosion by cycling the switch/cb. Use some electrical contact cleaner. I am a a&p.
 
Did it again today. Tapping the pump fixed it... for now. New pump on order and grounded till Tuesday.
 
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.
 
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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.
 
Dan Thomas said:
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.
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Yep —
 

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