Jumper fuel pump relay to drain stale gas

WERK I · WERK I's Garage

Hi Everyone,
My engine is about to go back into the 930 after a long hiatus for an engine rebuild and other family matters that entailed the car being out of action for nearly two years. I was thinking of using the fuel pumps to drain the tank of stale gas before putting the engine back into the car.
Have any of you drain a tank using this method? What did means of jumpering to get the pumps to turn on? Or is there another method without buying some auxiliary hardware to do this? I did turn the ignition switch to "On" to see if this would activate the pumps because the connector to the airflow meter is of course disconnected.....No pumps.

full quack · 08-09-2017, 03:00 PM

I would not want to run old crap gas thru my filter/pumps/accumulator. I suppose you could break the fuel line fitting before the engine, and use just the front pump.

But why not just drain the tank via the drain plug???? The lines will syphon clear just by unscrewing the exit fitting on the front pump. This will drain 99% of your old gas.

Mark

WERK I · WERK I's Garage

Really don't want to drain the tank via the drain plug. I want a more controlled method of draining. Turning the pumps on and off via a switch while I switch gas cans seems a far safer approach. Not worried about the fuel filter. Changing it anyway. Disconnecting line in front of the tank pump since there's little chance of maneuvering a gas can in that area due to the mid-rise lift I'm using.
One possibility is disconnecting hard line that goes through the tunnel and connects to the flex line going to the second pump. But if it can't drain safely and cleanly, I'm back to my original question.

turbobrat930 · 08-09-2017, 05:37 PM

Remember, there is also a fuel strainer attached to that drain plug. If you are draining old gas out of there I would go ahead and do it via the drain plug. Take a look at the strainer and make sure that everything is good and clean. And, draining the tank via the drain plug is not as uncontrolled as one might think. Just have a couple of 5 gallon gas cans available and a funnel and go at it.

JFairman · 08-09-2017, 05:43 PM

I've done it by removing the fuel feed hose to the fuel head. Then stuff the end of it into a larger inner diameter hose around 4 feet long that can handle gasoline.
Then put the other end of that hose into a container and turn the pumps on.

T77911S · 08-10-2017, 03:15 AM

remove the connector on the top rear of the AFM, remove the fuel line to the FD, put a hose on it to what ever then turn the key on.
I would also put a battery charger on the battery, set on 10amp.

how much gas are you talking about?
the car been stored inside?

WERK I · WERK I's Garage

Quote:

Originally Posted by turbobrat930

Remember, there is also a fuel strainer attached to that drain plug. If you are draining old gas out of there I would go ahead and do it via the drain plug. Take a look at the strainer and make sure that everything is good and clean. And, draining the tank via the drain plug is not as uncontrolled as one might think. Just have a couple of 5 gallon gas cans available and a funnel and go at it.

Wasn't aware of the strainer. I'll take a look. Thing of note, I did attempt to rebuild the fuel distributor since the car has been in an ethanol blend environment for the past several years. I expected to see corrosion and/or deterioration of seals. The thing was spotless. The plunger slits and each individual injector feed orifice show no signs of sediment or varnish. So I'll be curious about the state of the strainer. Car has about 77K miles on it.

Quote:

Originally Posted by JFairman

I've done it by removing the fuel feed hose to the fuel head. Then stuff the end of it into a larger inner diameter hose around 4 feet long that can handle gasoline.
Then put the other end of that hose into a container and turn the pumps on.

I may wind up doing this. I preferred doing it without the engine in the bay, but once I realized it wasn't going to work with the engine harness disconnected from the rear fuse/relay panel, I came to you guys for your experiences.

Quote:

Originally Posted by T77911S

remove the connector on the top rear of the AFM, remove the fuel line to the FD, put a hose on it to what ever then turn the key on.
I would also put a battery charger on the battery, set on 10amp.

how much gas are you talking about?
the car been stored inside?

The car has been stored inside, never below 50* F. The amount of fuel in the tank is about 15 gallons, 91 octane 0% ethanol. Disposing of the gas is a real PIA. In the area where I live, the hazardous material site is 20 miles away and appointments are necessary for disposal. I'm going to take two 5 gallon containers there and dilute the remaining stale with a full tank of racing gas and a bottle of Techron.

Thanks all for your input.

Ken911 · 08-10-2017, 05:23 AM

i always used the stale gas from draining the tank in the pick up. dump in 5 or 10 gallons then top off the tank with fresh gas truck never noticed it.

RarlyL8 · RarlyL8's Garage

First drain the gas:

Then remove the bung and tank filter and clean:

RarlyL8 · RarlyL8's Garage

WERK I · WERK I's Garage

Thanks for the great illustrations, Brian.

JFairman · 08-10-2017, 05:56 PM

The screen around the fuel pickup is nylon or something like it. Don't use a metal fiber brush to clean it. The toothbrush is OK and Harbor Freight has inexpensive black nylon brushes good for scrubbing delicate things like that in solvent.
The rest is brass and can take a brass brush or whatever. Use compressed air for final cleaning.

When I restored the gas tank in the car I used to have I reused the rubber oring on the brass and screen fuel pickup and smeared some blue hylomar gasket dressing on it because hylomar is not disolved or thinned by gasoline. There's other gasket sealers that will also work and a new oring would probably work well dry or with just a little oil smeared on it first to lubricate the oring and brass threads while screwing it in.

I didn't have a 22mm allen head wrench for it so I used the head of a 22mm wrench size bolt and turned the shank of the bolt with a pipe wrench to loosen and then tighten the brass fuel pickup screen thing.

RarlyL8 · RarlyL8's Garage

The pictures were of my gray slant when I first got it and began bringing it back to life. Now with the restoration shop we go through this process quite often. Cleaning fuel systems is very time consuming if you are not changing out all of the lines. We have a setup that uses a fuel pump with filter to recirculate through all the lines up to the accumulator. We let that run for several hours while cleaning from the accumulator to the injectors. Once the engine side is clean you absolutely do not want any chance of recontaminating.

JFairman · 08-11-2017, 04:44 AM

At todays labor rates it's way cheaper to buy new fuel lines and replace them. Way safer too because the rubber outer layer of the 30 year old fuel lines will be dry rotted and the inner rubber of the hose will be compromised by the ethanol in todays gas and they should all be replaced by now.

audiadj · audiadj's Garage

I've removed the tank fuel sending unit and used a cheap plastic siphon bulb pump with a long tube to reach into the tank. The output tube was connected to a long hose that drained into a gas can. You may want to buy a new sending unit gasket interface to the tank. I've drained close to a full tank, 20 gallons, on my '79 930

If your car is old I would be a little leery of pulling the drain plug and scr****ing up the threads.