Reverse polarity on fuel pump to unstick it

[Iconic]

I just joined and this is my first post.
I'll try to make it short.
How bad (or good) of an idea is it to send current through the fuel pump in opposite polarity than it is supposed to be (for the purpose of unsticking it).
It is a new style (1970 280 SL). Theoretically, hasn't run in 3 years. Fuel tank is almost full, so I'm hoping no rust, just "gelled" up.
Bad idea, or good idea?
Thanks.

[al_lieffring]

I think there is a check valve in the discharge port of the pump, so reversing the polarity could possibly break free a stuck impeller, but it wont backflush the system. If you dont hear the pump whirring when the key is switched on turn it off, it will over heat quickly without fuel circulating.

most likely the strainer in the tank drain plug is clogged up and will need cleaning.

[scoot]

I think there is a check valve in the discharge port of the pump, so reversing the polarity could possibly break free a stuck impeller, but it wont backflush the system. If you dont hear the pump whirring when the key is switched on turn it off, it will over heat quickly without fuel circulating.

most likely the strainer in the tank drain plug is clogged up and will need cleaning.

I ran mine in reverse recently, but it wasn't gummed up.   I just put the wires on the wrong way.    But the OP has 3 year old gas -- not nice.  I don't think you want to run the fuel pump if you can help it, at least not until you get the gas of the tank.  I would try draining the tank from the hose that goes to the fuel pump, into multiple big gas cans.  (nasty stuff, what can you do with it?!)     I would try draining the gas tank and then reversing the polarity and see if it unsticks the pump, and I agree, you should turn on the key and hear the pump.  If you don't, turn off the key.

I assume you have checked that power is going to the pump, right?

Don't run the 3 year old gas through your injector pump if you can help it.  That could be kind of bad.

[glenn]

The pump impellor is about 2" in dia with 1/4" teeth.  It gets gummed up and sticks to the end cap(held on by 6 screws) that it drops on to when the pump is not running.   Drain the tank, remove the pump, take off the in and out pipes.  Fill the impellor cavity with solvent to dissolve the gunk.  If that doesn't work, take the end cap off(a thrilling task!) and free up the impellor.   Mind the safety considerations around gasoline.

[Iconic]

Fill the impellor cavity with solvent to dissolve the gunk.   Mind the safety considerations around gasoline.

All good comments (from all of you). Thank you !
What solvent should I use to dissolve the gunk that is created from old gas?
Will I be able to see the impeller through the input or output of the pump?
I'm not thrilled about dealing with ~15 gallons of old fuel, so I am taking this very slowly.
I don't have power to the pump, but that is a different story.... I'm bringing power straight from the battery (carefully), but so far, only with the correct polarity.....
Mark

[scoot]

I think we need a new thread called "How to safely and greenly dispose of 15 gallons of old gasoline".

[glenn]

I think we need a new thread called "How to safely and greenly dispose of 15 gallons of old gasoline".

Add 2 filtered gallons of it to your other car when it is 2 gallons low, run til empty.  Repeat 7 and a half times.   Gasoline doesn't alchemize to gold or    Old gas may be less of a polutant than today's corn crap.

[scoot]

Add 2 filtered gallons of it to your other car when it is 2 gallons low, run til empty.  Repeat 7 and a half times.   Gasoline doesn't alchemize to gold or    Old gas may be less of a polutant than today's corn crap.

I didn't think of it as being less of a polutant.  I thought of it is being sort of laquery goo that might really mess up fuel injection and other expensive things.   I would feel safer running it in an old carburated car than in a "modern" car...

[Peter van Es]

Add 2 filtered gallons of it to your other car when it is 2 gallons low, run til empty.  Repeat 7 and a half times.   Gasoline doesn't alchemize to gold or    Old gas may be less of a polutant than today's corn crap.

Alternatively: Add 2 filtered gallons of it to your other neighbour's car when it is 2 gallons low

Peter

[glenn]

Key word-'filtered'.   Run it in your lawnmower, etc.   Remember, all the gunk, junk, crap has already settled out.  It is on the bottom of the tank, in the electric pump welding the impellor to the body, in the FI pump grabbing the pistons, in the hoses plugging them.   Seems like what's left in the remaining gasoline might be pretty good after all. 

PPP  Piddling Pagoda Persiflage

[Iconic]

FYI: You have all convinced me, I will not send that gas through my fuel injection.
The county I live in takes old gas at the Hazardous Waste facility. So, now that I know that, it is no big deal to drain the tank and dispose of it properly, with no risk to my other vehicles/mower.
As it turns out, maybe I am lucky that the pump didn't pump because of what it would have pumped into the rest of the system.
Thanks for all of your help.
Mark

[joao210]

I have had considerable experience in this area  Remove the cover over the pump Take the hose off the pump that goes to the tank and drain the tank Remove the plug in the centre of the tank A little more fuel will come out  Use a bolt head stuck into the hexagonal hole and grab the threaded part with a pipe wrench or large vice grips The correct size I believe is 22mm allen which is uncommon Clean the screen It will have either a yellow gum which is best removed with oven cleaner or red orange powder residule best removed with carburetor cleaner You could drop the tank and remover the fuel sender and clean the tank but it is not necessary Discard the hose that goes from fuel tank to pump and replace with new neoprene hose[ from parts store] Place  a clear opaque  in line fuel filter  half way in the  line to pump[the old hose if original may throw junk through as it disintegrates ]Save the hose that goes away from the pump and cut off the swaged fitting so that that line can also be replaced with a generic hose using clamps  Disconnect the metal line at the INJECTION pump that goes to the fuel pump and blow compressed air through it[you might get away with carb cleaner if air isnt available] On the intake side of fuel pump there is a large threaded fitting remove it and clean the screen On the exit side there is also a fitting with a check valve put carb cleaner into fitting and tap gently with a screwdriver You shouldnt be able to blow into it with your mouth when it is clean Apply electric  and the pump it should turn freely If not put the positive wire  onto the negative  terminal and  tap the negative wire onto the positive terminal Do this for about 100+ times  If it doesnt free up remove the screws from the bottom of the pump DO NOT MESS WITH THE IMPELLOR BLADES remove the impeller using a pick and the small holes in the middle Clean the chamber and replace the impeller cover Retest pump  and make sure to use a hot battery If you want to wet test it use a 5 gallon bucket 1/4 full of diesel NOT GASOLINE Dunk the hose on the intake side in the fuel let it bubble and raise it  up   several times  to let fuel into pump   the new slyle  pump has to be primed [the old style pump is self priming] Replace the pump onto vehicle When the pump is working you will need to crack open the fuel lines at the injectors and crank the engine till a little fuel comes out of each one Once the car starts keep an extra in line fuel filter in the trunk and check frequently If you dont have a filter between the tank and pump you will have to remove the pump each time the tiny filter in the pump plugs up

[Benz Dr.]

Add 2 filtered gallons of it to your other car when it is 2 gallons low, run til empty.  Repeat 7 and a half times.   Gasoline doesn't alchemize to gold or    craOld gas may be less of a polutant than today's c.orn p

Where did you get that from? Ethanol is a lot cleaner burning that gasoline.

[Benz Dr.]

Contary to popular opinion, you can run the pump dry. I wouldn't leave it running for a long time but a short test won't hurt it. I put a bit of oil in the pump while I test them.

Changing polarity won't get the pump to move it it won't turn to begin with. Once you get all that old spooge in there it's going to stay stuck until you take it apart and clean it out. Depending on how long it was sitting you might need to do a lot move cleaning. That old stuff with continue to desolve and may jam the pump later on.

I usually dress the upper side of the pump cover cover if I take it off. It's also a good idea to mark the position before removal.
Take a piece of flat glass and get a round piece of sand paper with a sticky backing and place it on the glass. Take the bottom cover of the fuel pump and place it on the sand paper and move the cover in a swirling motion. Check the cover to see how it looks and keep swirling until all the marks are gone and there are no high spots left. This procedure will make the cover perfectly flat which is very important. This will also make the pump tighter inside and it will pump almost like a new one.

Start with 220 grit and then go to 400 for a nice finish.

I use a spark plug socket to remove the drain plug from the fuel tank. Get a socket that has a 1/2 drive on it and remove the rubber grommet that holds the spark plug in place. Place the socket into the drain plug open end down. Get a long extension and fit it through the bottom of the socket. It will remove it no problem.