DEFUNCT MOTOR

[nomad 11]

i know this has nuthing to do with metal detecting. but so what right ? its still tech talk. and its puzzling so i need to know. the motor quit. so what id like to know is ? can i check the resistance of the two terminals to possibly determine what went wrong internally ? brushes wore out ? which is the most likely ? so if the brushes wore down to nuthing i should get 0 resistance ? is that right ? or it seized ? also just want to say this is a fuel pump motor about 7 inches long and if it lasted almost 27 years in my old van then it was a good run huh

 

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[djackson7348]

0 ohms resistance is a dead short. An open circuit will show infinite ohms or at least an extremely high number of ohms.

 

[smokeythecat]

Bottom line is - try to find a new one. No one fixes these anymore that I know of. Kudos on getting it out!

 

[A2coins]

If the pump is in your tank its easier to cut an access panel then to drop the whole tank not sure how yours is set up just 2 cents

 

[Toecutter]

Its a DC motor inside, if you can get it apart you might be able to get a new motor...

 

[SD51]

0 ohms resistance is a dead short. An open circuit will show infinite ohms or at least an extremely high number of ohms.

Like djackson stated, if your getting 0 ohms, the motor is shorted and would have blown the fuse in the circuit. If your reading an open with the ohmmeter, the motor is shot. I'm assuming you confirmed that the fuel pump relay is working properly and proving 12 volts to the fuel pump motor when the car is started.

Here's a wiring diagram for a fuel pump...

 

[boogeyman]

Take it down to pick a part with a 12v motorcycle battery to test. Cheaper easier & more fun. Used to buy fuel pumps for VWs for $3. A pair of needlenose pliers, a new O ring & a piece of thread topped off with a spritz of paint. They sold like hotcakes at the VW clubs.

 

[nomad 11]

Bottom line is - try to find a new one. No one fixes these anymore that I know of. Kudos on getting it out!

its all ready done. i just want to know why it failed. the only way to open it up would be tear the metal casing. which would mean not being able to reuse it. theres no way to rebuild the motor itself and reuse it. it was definitely a nail biter getting it out and back together. still trying to recuperate 2 months later. cant wait for warmer weather to have a couple brews and catch a quicky buzz.

 

[nomad 11]

so before i tear it apart ? the wider prong would be what the positive post right ? and if i check it with a multimeter if the brushes are worn all the way down that would mean a short then correct ? and i should get what reading ? now if the brushes did not wear all the way down ? which i think is improbable because as i said its almost 27 years old. and the way the lock ring was rusted in it has to be the original from the factory. just to let u know this is a Walbro pump. so if anybody was ever on the assembly line that assembled these ? thanks. and rest in peace Lee Iacocca a job well done

 

[nomad 11]

If the pump is in your tank its easier to cut an access panel then to drop the whole tank not sure how yours is set up just 2 cents

well if anybody offers me their 2 cents i prefer indian heads

 

[nomad 11]

Like djackson stated, if your getting 0 ohms, the motor is shorted and would have blown the fuse in the circuit. If your reading an open with the ohmmeter, the motor is shot. I'm assuming you confirmed that the fuel pump relay is working properly and proving 12 volts to the fuel pump motor when the car is started.

Here's a wiring diagram for a fuel pump...

View attachment 1800613

yeah i'm long past all this. thank God. thanks though

 

[DDancer]

Several things come to mind, one is that the brushes are worn out~ this would mean no electrical contact between the brush and the armature and an open circuit or the contacts of the armature are worn causing the same condition. Excessive carbon and or arcing deposits on those areas can do the same thing but on a multimeter they may show continuity or high resistance but the contacts wont be good for power transmission. Then it could be that the windings of the armature have opened, again no continuity so an open circuit. There could be and internal short either to the brush, armature or windings and my last thought would be that the internal bearings for the armature are shot creating enough resistance that the motor can not turn properly or at all.
Lots of things can make a motor go bad. Electrical testing and tear down and inspection are the only way to know what happened. Rebuilding those type's of motors is likely to be more of a problem then just replacing it but if you want to take the time and try have fun.

 

[nomad 11]

ok. I finally mustered up the will or ambition to get my multi meter out and check for resistance of my little kaput motor. I asked if the large prong earlier if the large prong was the positive side and nobody told me. now I looked and it wasn't marked either. so I just had to presume it was. not red or black either. so I got a reading of about 250 ohms. so I guess this means the brushes aren't completely worn down that that would be shorting out. would that be correct ? so ?

 

[releventchair]

Not saying it's right....We theorized that "flat" spots in a winding could stop a fuel pump.
The sporadic ,couple times after initial fail they would run was part of why we thought that.
They are good. Or bad.
One might run when power is applied after removal from tank , but that does not mean it is "good".

 

[nomad 11]

Not saying it's right....We theorized that "flat" spots in a winding could stop a fuel pump.
The sporadic ,couple times after initial fail they would run was part of why we thought that.
They are good. Or bad.
One might run when power is applied after removal from tank , but that does not mean it is "good".

no i tried that. presuming the wide terminal was positive ? must be a big secret ? i hooked it to my car battery with jumper wires. maybe that would be exposing to much current directly ? but it wouldnt even attempt to spin or even growl ? if i was to say ? hook it to a 9 volt battery and the motor was in good shape would that be enough to turn it over ? or would it still be lacking the amps ?

 

[SD51]

You stated you read 250 ohms across the terminals. Per Ohms Law, I (current in Amps) equals Volts divided by Resistance (Ohms).

In your motor, current draw is 12 Volts divided by 250 Ohms which equals .048 Amps or a current draw of 48 milliamps, which is no problem for your car battery to supply.

 

[nomad 11]

You stated you read 250 ohms across the terminals. Per Ohms Law, I (current in Amps) equals Volts divided by Resistance (Ohms).

In your motor, current draw is 12 Volts divided by 250 Ohms which equals .048 Amps or a current draw of 48 milliamps, which is no problem for your car battery to supply.

ok good answer. but what i was wondering was ? if directly applied to the motor itself. not going through the relays and all the wiring like it normally would all the way back to the gas tank. maybe that would be overload ? huh ? maybe ?

 

[SD51]

Good question, here's a video that shows what the typical current draw is for a electric fuel pump.



The video shows a good electric fuel pump is drawing just over 5 amps.

If there was an overload, the fuse for that circuit would blow.

Your pump should have a resistance just over 2 ohms. Afraid it's time for a new pump.

 

[nomad 11]

Good question, here's a video that shows what the typical current draw is for a electric fuel pump.



The video shows a good electric fuel pump is drawing just over 5 amps.

If there was an overload, the fuse for that circuit would blow.

Your pump should have a resistance just over 2 ohms. Afraid it's time for a new pump.

ok another fine answer. new pump was installed almost 3 months ago now. as soon as i work up the ambition to tear the old pump apart. i'll assess what went wrong with my old one ? i know the suspence is killin some of ya ? ya have to cut a zombie some slack. cuz i know some of ya have about as much patients as some of these doctors. HA ! HA ! not that they dont deserve it. thanks for the help

 

[DDancer]

To answer your question as to whether the motor hooked directly to the battery of your car would over load it, it would not unless it was directly shorted out. There is no difference in wiring it directly or thru the vehicles wire harness unless there is a resistor somewhere in the line~ typically not~ and it would show up in the wiring diagram. Also a 9v battery may not have the potential to run a 12v motor and if it did it would not run very long.
SD51 made the observation that your motor should have a resistance of around 2 ohms, most good motors have a very low resistance, so at 250 ohms its definitely burnt out as the increased resistance lowers total current required to drive the motor. My thoughts.