Let's talk about electric fuel pumps

Chrisgoesflying

Chrisgoesflying

Cleared for Takeoff
Joined
Dec 7, 2018
Messages
1,105
Location
Too far north
Display Name
Display name:
Chrisgoesflying
The auxiliary electric fuel pumps (two of them) on my Piper Comanche 250 went kaputt. No more tic tic sound when turning them on. My mechanic checked if current is flowing to them and it was the case, hence the conclusion is, the pumps are done. I checked the parts catalog and found out I need the part number 481-666. Quick research shows that McFarlane has an STC'd pump to replace P/N 481-666 for $300 each. Quick search on Texas Air Salvage was showing several used ones with part number 481-666 for $125 each. So, I ordered the two best looking ones from Texas Air Salvage. Again, both indicated P/N 481-666 in the listing. Today I receive the invoice and now both indicate the P/N 478-360. One being from Bendix, the other one being from Facet (Gold Flo). I check P/N 478-360 and Facet Gold Flo and on the Facet website, they clearly say the pump is not for aviation use. I couldn't find anything about the Bendix one with the P/N 478-360 regarding use for aviation. Comanche parts catalog does not list P/N 478-360 as an eligible fuel pump. Is 478-360 and 481-666 the same? Can the Facet pump be legally installed in a certified airplane (it came off of a PA-28)? If they are the same pumps, why the different P/N? I'm close to just cancelling the order and pony up for the STC'd pumps (which look exactly the same by the way) just to be on the safe side. Would hate to give the insurance or an overzealous ramp check agent any reason to not cover or fine me.
 
A light rap will sometimes clear the issue with these type pumps.
 
They’ve busted IAs for signing off unapproved parts for as long as I can remember. My old mechanic got a 90 day license suspension for a not-approved LED light!
 
Doc Holliday said:
What's a ramp check agent? And why would they be opening your airplane and inspecting it?
Click to expand...

I’m north of the border. There are fines for sneezing the incorrect way lol. I guess they wouldn’t have to open the cowl to see they’re the wrong pumps. The logbook would give it away. Also, the bigger concern is insurance. If I happen to bend some metal due to a pump failure, couldn’t the insurance company say “too bad, those were the wrong pumps”?
 
Insurance wouldn’t care unless the pump caused the accident. In the States I doubt an IA would sign off unless they could verify the application on an AML.
 
Stewartb said:
Insurance wouldn’t care unless the pump caused the accident. In the States I doubt an IA would sign off unless they could verify the application on an AML.
Click to expand...

I’m not too sure about that. The Facet Gold Flo pump was on a certified U.S. Cherokee. I don’t see that pump being a legal part for the Cherokee or Comanche (despite the fact that it is the same pump as the “legal” ones) based on the parts lists of the airplanes. Plus, Facet writes that the pumps are not for aviation use, not because they are bad but simply because they didn’t go through the hassle of certifying them. So, either the owner installed them without a logbook entry or an IA signed off on it. Either way, it was in the inventory of TAS with the correct part number but then they clarified after my order that it’s actually a different part number.
 
Mtns2Skies said:
"pony up"? dude it's less than a $200 difference. That's less than it takes to fill one of your fuel tanks. Why was this even a question to begin with when you're talking about a critical component to your SINGLE engine?
Click to expand...

I need two pumps on the Comanche, plus shipping, plus import duties. The difference is around $600. That in plastic dollars is around $800. My rule of thumb, if the used part is less than half the price of the new part, I tend to buy used.
 
Last edited:
Mine went out and I had a hard time finding one, was on a 6+ month waitlist, bought one on eBay but then got a brand new one (I called the manufacturer and they sourced one for me within an hour) I think it was $1200, I want my fuel pump to work and now I treat my fuel pump better and only use her when needed.

I did find the exact part number, I would go for the same part number but you can see what will fit in the spot too. Sometimes it’s the angle of the inlet/outlets and I think mine is attached to the firewall and the space is tight in there you need it to be the right size.
 
Now, depending on the serial number of your airplane, the pumps are quite likely wired like this, as shown in the Comanche service manual:

1689873192146.png

If so, that is a really unfortunate arrangement. Since both pumps went out at the same time, that whole circuit is suspect. The pumps are fed off the bus through one breaker and one switch.

Ohm's Law has interesting things to say about this. If the mechanic disconnected the wires at the pumps and measured the voltages, he might have found them just fine. But if he had reconnected them and measured the voltage again, he might have found both with almost no voltage.

That's because, in old airplanes, the contacts in switches and breakers oxidize with age. That oxide represents a small amount of resistance. That resistance causes a little bit of heating, which accelerates the oxidation, which increases the resistance, and soon enough the circuit doesn't work anymore because insufficient current is getting to the components. Replacing the components won't fix this scenario. Replacing the defective switch or breaker will.

The key is knowing how to isolate the bad part. Master on, pumps on. Take a voltage reading between ground and bus. Should show 12V. Leave the meter's ground lead connected to ground. Take a reading at the breaker's bus terminal and output terminal. Both should read 12V. If the output is low, the breaker is bad. If it's ok, take the next readings at the switch. If the switch's input is low, the wire from the bus is bad. If not, and the output is low, the switch is bad. If it's ok, take another reading at the pump. If it's low, somewhere along that line there's a problem, maybe a corroded or loose crimp terminal.

This sort of thing causes unnecessary battery and starter replacements. Expensive. Much of the time it's a $40 master or starter contactor. Their contacts oxidize and burn, too. It takes very little resistance to cause a big voltage drop with huge currents like that.

In Cessna's restart airplanes, they demand master and avionics switch replacements at, IIRC, 1000 hours or four years, due to exactly this problem. They also want aux fuel pumps replaced at ten-year intervals. This stuff shouldn't be run to failure.
 
Last edited:
Dan Thomas said:
Now, depending on the serial number of your airplane, the pumps are quite likely wired like this, as shown in the Comanche service manual:

View attachment 119170

If so, that is a really unfortunate arrangement. Since both pumps went out at the same time, that whole circuit is suspect. The pumps are fed off the bus through one breaker and one switch.

Ohm's Law has interesting things to say about this. If the mechanic disconnected the wires at the pumps and measured the voltages, he might have found them just fine. But if he had reconnected them and measured the voltage again, he might have found both with almost no voltage.

That's because, in old airplanes, the contacts in switches and breakers oxidize with age. That oxide represents a small amount of resistance. That resistance causes a little bit of heating, which accelerates the oxidation, which increases the resistance, and soon enough the circuit doesn't work anymore because insufficient current is getting to the components. Replacing the components won't fix this scenario. Replacing the defective switch or breaker will.

The key is knowing how to isolate the bad part. Master on, pumps on. Take a voltage reading between ground and bus. Should show 12V. Leave the meter's ground lead connected to ground. Take a reading at the breaker's bus terminal and output terminal. Both should read 12V. If the output is low, the breaker is bad. If it's ok, take the next readings at the switch. If the switch's input is low, the wire from the bus is bad. If not, and the output is low, the switch is bad. If it's ok, take another reading at the pump. If it's low, somewhere along that line there's a problem, maybe a corroded or loose crimp terminal.

This sort of thing causes unnecessary battery and starter replacements. Expensive. Much of the time it's a $40 master or starter contactor. Their contacts oxidize and burn, too. It takes very little resistance to cause a big voltage drop with huge currents like that.

In Cessna's restart airplanes, they demand master and avionics switch replacements at, IIRC, 1000 hours or four years, due to exactly this problem. They also want aux duel pumps replaced at ten-year intervals. This stuff shouldn't be run to failure.
Click to expand...

He thoroughly checked to make sure it's the pumps and not the switch or breaker. He suspects that one pump must have been inop for a while (I only recently bought the plane) but since they're both connected to the same switch, I never really noticed because the operating pump still gave me tic tic tic and fuel pressure before startup. Then, the second pump failed and I noticed it obviously.
 
I should have elaborated a bit on why Ohm's Law matters here.

Disconnecting the wires at the pumps removed the load path to ground. The voltmeter needs only a few microamps to make it read, and it will show 12V at the ends of those wires. The resistances in the breaker or switch or bad crimp terminals won't drop the voltage perceptible with a low current draw like that. But those pumps want a few amps apiece, and that will cause major voltage drops across the bad stuff, and a big voltage drop means a big current drop, since voltage is the pressure that drives the volume, or amperage, and those pumps need the volume.

E + IxR. Voltage equals current times resistance. If we have a ten-ohm resistance in a breaker, for example, and we take a voltage reading at the disconnected pump wires, a 10-microamp draw will reduce the voltage 10 x .000001 = .00001 volts drop. Can't really see it. If the draw, pumps connected, is 10 amps (might be more or less), we get 10 ohms x 10 amps = 100 volt drop. A 100-volt drop in a 12V circuit is obviously impossible, but you get the point. The pumps don't run. It wouldn't take anywhere near a ten-ohm resistance to do it, either.
 
RyanB said:
Dude, fuel pumps are not something to try and cheap out on. Just buy the right one for your application and be done. Spruce should have them all.
Click to expand...
I gotta go with this assessment. To me, it just doesn't make sense to buy that kind of used part from Texas Air or others. The pump you're replacing is, maybe 40-50 years old, if the original. So, the used one runs, but maybe it's 39 years old? Sure, more money, and unfortunately, the McFarlane STC pump has a 5-year life limit, but, so be it.
Have you tried Kadex Aero? Don't know if they have what you need, but at least it would avoid customs/import fees.
 
Chrisgoesflying said:
The auxiliary electric fuel pumps (two of them) on my Piper Comanche 250 went kaputt. No more tic tic sound when turning them on. My mechanic checked if current is flowing to them and it was the case, hence the conclusion is, the pumps are done. I checked the parts catalog and found out I need the part number 481-666. Quick research shows that McFarlane has an STC'd pump to replace P/N 481-666 for $300 each. Quick search on Texas Air Salvage was showing several used ones with part number 481-666 for $125 each. So, I ordered the two best looking ones from Texas Air Salvage. Again, both indicated P/N 481-666 in the listing. Today I receive the invoice and now both indicate the P/N 478-360. One being from Bendix, the other one being from Facet (Gold Flo). I check P/N 478-360 and Facet Gold Flo and on the Facet website, they clearly say the pump is not for aviation use. I couldn't find anything about the Bendix one with the P/N 478-360 regarding use for aviation. Comanche parts catalog does not list P/N 478-360 as an eligible fuel pump. Is 478-360 and 481-666 the same? Can the Facet pump be legally installed in a certified airplane (it came off of a PA-28)? If they are the same pumps, why the different P/N? I'm close to just cancelling the order and pony up for the STC'd pumps (which look exactly the same by the way) just to be on the safe side. Would hate to give the insurance or an overzealous ramp check agent any reason to not cover or fine me.
Click to expand...

So for $600 (plus taxes, shipping, etc) you can have two brand-new pumps? Why are we even talking about this?
 
RyanB said:
Because he's wanting to be cheap on parts that he shouldn’t be cheap on. There, I said it.
Click to expand...
I mean - hell's bells, there's cheap then there's. well... something else.

To OVERHAUL the electric pump on mine was $1,100. If I could have bought a new one for less than the price of the overhaul it'd be right there.

These things are CRITICAL and not to be shortcut with sketchy used spares, labeled "not approved for aviation" or "for display purposes only" or whatnot.
 
Rgbeard said:
I mean - hell's bells, there's cheap then there's. well... something else.

To OVERHAUL the electric pump on mine was $1,100. If I could have bought a new one for less than the price of the overhaul it'd be right there.

These things are CRITICAL and not to be shortcut with sketchy used spares, labeled "not approved for aviation" or "for display purposes only" or whatnot.
Click to expand...

I fully agree. If you had read the thread, you would have seen that this is exactly why I posted this question. I ordered parts I assumed (because they were labelled as such) were original, authorized parts for my aircraft that had less hours and were newer than my pumps which have given up after 60 years and 3,000 hours in service. So my options were, buy two used original parts that may be good for another 20 years with no life limit on them for $250 or buy two STC’d parts for $600 every five years (due to the life limit on the STC). When I found out that the pumps actually had a different p/n than advertised, at that one that refers to a pump that is labelled “not for aviation use”, I came on here to seek advice about the correct part numbers. Call it cheap if you’d like but these pumps can last 60 years. My current ones did apparently. If I buy 30-35 year old, original parts, I can reasonably expect them to last another 20 years. Suddenly, we’re looking at a difference of $250 vs $2,400 plus shipping, tax and installation.
 
Rgbeard said:
I mean - hell's bells, there's cheap then there's. well... something else.

To OVERHAUL the electric pump on mine was $1,100. If I could have bought a new one for less than the price of the overhaul it'd be right there.

These things are CRITICAL and not to be shortcut with sketchy used spares, labeled "not approved for aviation" or "for display purposes only" or whatnot.
Click to expand...

I recommend:

Home - Aeromotors

aeromotors.azurewebsites.net aeromotors.azurewebsites.net

Overhauls take a week, plus shipping times…and cost runs about $500.
 
Chrisgoesflying said:
Call it cheap if you’d like but these pumps can last 60 years. My current ones did apparently. If I buy 30-35 year old, original parts, I can reasonably expect them to last another 20 years.
Click to expand...
Don't bet your life on it. Those pumps have switches in them too, and those switches oxidize and burn, which is maybe why yours quit. A 35-year-old pump ight have badly oxidized switches even with low hours if it's been sitting in some damp salvage depot warehouse, or in a derelict ramp queen, for years.
 
Those pumps that go tik-tik have a mechanism like this in them:

1689958006627.png

With the rod to the left, the contacts close, the solenoid is energized, and the rod is pulled to the right. It pulls on a diaphragm that sucks fuel in past the inlet valve. A plate on the rod compresses the return spring against the fixed plate nest to the solenoid. The contacts open, the return spring forces the fuel out past the exit valve at the right pressure until the contacts close again and the diaphragm pulls more fuel into the pump.

Those contacts oxidize and burn. They make a spark every time they open, and sparking is arcing that slowly destroys the contacts. The diaphragm is a fabric-reinforced rubber that ages and deteriorates like all polymers, especially in contact with gasoline.

Which is why Cessna, who use this sort of pump in a number of their airplanes, demands periodic overhaul or replacement.
 
Wow, that is remarkably similar to the S.U. pumps used on many British cars 1920s-1970s. I grew to despise them because I had to replace the points quite often on the unit in my 1960 SAAB. Like post #3 said, whacking them temporarily fixes them. Finally, my uncle gave me an NOS 6V unit which I installed with a dropping resistor; this worked for the rest of the time I had the car. When the pump on my 1969 MG Midget died, I replaced it with a non-S.U. type. Just a few years ago, I found out that the pumps have a failure mode which is very hard to detect. To reduce arcing of the points, they had a 90 ohm non-serviceable resistor in parallel with the solenoid coil, much like old mechanical voltage regulators. When the pump fails with the points welded together there is battery voltage across the resistor 100% of the time so it overheats and burns up. If you "fix" the unit by replacing the points there is now lots of arcing and it doesn't last long. Best practice is to replace the points and diaphragm every 5 years or so and it won't fail.
 
In 1975 I bought a nearly-new Ford Courier, one of the mini-trucks popular at the time. Made by Mazda. Good truck, except for that fuel pump. It went out three or four years after I bought the truck, and the Ford dealer sold me a different pump, similar to this one, since those original pumps were such a pain:

1689976806052.png

Pumps like that have an electronic oscillator that drives a solenoid that propels a plunger back and forth rapidly to move the fuel. No diaphragm, no contacts. That pump lasted me until I sold the truck years later.
 
I ended up buying two new STC'd pumps. One thing I noticed is, the FAA STC of the PMA pumps mandate a life limit of 5 years. The French STC of the exact same pump (that document is also available directly on the McFarlane listing of the pump) states "the pump has no life limit". Makes you wonder what in the French air allows these pumps to last more than five years lol. I wonder if I can get the pumps installed under the French STC on my Canadian registered airplane?
 
Ask TC if you can use the French data as an AMOC.

Personally I would think the 5 years would be about right to replace.
 
Chrisgoesflying said:
I ended up buying two new STC'd pumps. One thing I noticed is, the FAA STC of the PMA pumps mandate a life limit of 5 years. The French STC of the exact same pump (that document is also available directly on the McFarlane listing of the pump) states "the pump has no life limit". Makes you wonder what in the French air allows these pumps to last more than five years lol. I wonder if I can get the pumps installed under the French STC on my Canadian registered airplane?
Click to expand...
Are they installed under PMA or STC? 2 different paths with different data. If the original pumps are not life limited in TC specs, and you install as PMA, you should be good. You are only bound by STC if you install using the STC. Just the opinion of one guy on the internet, but I suggest a chat with your A&P.
 
Chrisgoesflying said:
I ended up buying two new STC'd pumps. One thing I noticed is, the FAA STC of the PMA pumps mandate a life limit of 5 years. The French STC of the exact same pump (that document is also available directly on the McFarlane listing of the pump) states "the pump has no life limit". Makes you wonder what in the French air allows these pumps to last more than five years lol. I wonder if I can get the pumps installed under the French STC on my Canadian registered airplane?
Click to expand...
Since you're in Canada you could make the argument that if the log entry was in French the French STC would be appropriate, eh?;)
 
Doc Holliday said:
Personally I would think the 5 years would be about right to replace.
Click to expand...

Murph said:
Based on what?
Click to expand...
Cessna has a Service Bulletin on replacement times for their pumps, SEB94-7. I can't find an online copy.

But I do see this:

We were told by users, maintenance shops and overhaul facilities that engine-driven and aux pumps routinely last to engine TBO. The manufacturers call for overhaul at engine TBO or at a calendar-year interval, most commonly 10 to 12 years.

From https://www.aviationconsumer.com/maintenance/fuel-pumps-overhaul-on-condition/
 
Having two pumps fail both at the same time would be extremely unusual. I would do some more digging and try to figure out why they failed before putting new ones on again otherwise the new ones are just as likely to fail as well. .
 
kmacht said:
Having two pumps fail both at the same time would be extremely unusual. I would do some more digging and try to figure out why they failed before putting new ones on again otherwise the new ones are just as likely to fail as well. .
Click to expand...

We don't know if both failed at the same time. Chances are one has been dead for a while. I bought the plane only 20 hours ago so couldn't ever really establish what two working pumps should sound like and what sort of pressure they should give me. My previous plane (Cherokee) had one of these pumps. During startup, it heard tic tic tic and the pressure gauge went up so all good. But chances are it was just one of them working. I'll see/hear if it's any different once two new pumps are in it.
 
Dan Thomas said:
But I do see this:
Click to expand...

I'm fairly new to airplanes but have some history with fuel pumps. 5 years just seems....wrong.....I'm really curious as what would have brought that about.
 
Murph said:
I'm fairly new to airplanes but have some history with fuel pumps. 5 years just seems....wrong.....I'm really curious as what would have brought that about.
Click to expand...

Maybe we should just fly them until failure, like so many owners like to do, or even better get an old used one out of the junkyard and hope for the best. :rolleyes:
 
Doc Holliday said:
Maybe we should just fly them until failure, like so many owners like to do, or even better get an old used one out of the junkyard and hope for the best. :rolleyes:
Click to expand...




As I said, I have a history with fuel pumps, and a failure in less than 5 years sounds more like a faulty batch of pumps that an excepted level of performance...Your personal preference was 5 years...why 5? why not 3? 7? My personal plane has an electrical and mechanical fuel pump, A failed fuel pump in flight means I'm going to land with one item not completed on the check list. I personally don't know of a person with a Cherokee thats changed a fuel pump prior to failure. Is it a good idea? Why not...change it every fifth annual. Why not change out cylinders before they show any sign of failure? We all know they fail.. lets get ahead of the curve.. My electric fuel pump spools up and sounds like it did the day I bought the plane, it hits the same pressure on the fuel pressure gauge as well. If it died tomorrow I'd look for some one that changes theirs out every 5 years for my replacement ..
;)


I do good to fly 60 hours a year...where as the same plane in a flight school is going to do what ? 1000 hours? Gallons of fuel pumped ( or hours ran) would be a better bench mark than a fixed time period in my experience.
 
Last edited:
You must log in or register to reply here.
Back
Top