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Practicing Infidel
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15,299 Posts
Discussion Starter · #1 ·
I pulled my relay (fuel pump) out yesterday when I was moving my underhood toolbox around.

Never got back to plugging it in and forgot about it.

This morning I fire it up, drive to the back of the property and shut her down.

I mow the grass and then fire up the Bronco to move it (for to cut under it) and it starts to run rough but still runs.

Then I remember I'd pulled out the relay harness yesterday.

How come it still runs ?????

Sixlitre
 

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Satyr of the Midwest
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17,738 Posts
How long did you let it run, though? There may have been enough pressure in the rails for a short time, plus the pressure in the tank above the fuel might've helped.
 

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Registered
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163 Posts
Aren't there two pumps on an '86? Do they both run off of the same relay or are they separate? Maybe the high pressure one was still running, pulling gas through the low pressure one in the tank...
 

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Enjoy my
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6,054 Posts
Aren't there two pumps on an '86? Do they both run off of the same relay or are they separate? Maybe the high pressure one was still running, pulling gas through the low pressure one in the tank...
If so that puts a ton of strain on the other pump...
 

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House of Windsor 4ever!
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10,565 Posts
Somehow, you're getting cross-fed power to the pumps. When your truck was waylaid a few months back, didn't your mechanic have to do some electrical work having to do with the pumps?
 

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Practicing Infidel
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15,299 Posts
Discussion Starter · #7 ·
Great ideas from everyone

I'm going to check and make sure;

1.) that's the right relay

2.) If Dave did anything to them

3.) if only one pump is running when the relay is unplugged.

4.) how long it will run for. It only really ran for 200 yards and one more start up.

Thanks

Sixlitre
 

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224 Posts
Your BKO was not really running, but rather being pulled by a magical team of unicorns (only theory I hadn't heard) :)

Maybe that's a good sign? Kinda like you'll never be able to kill the thing?
 

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Zombie Hunter
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13,687 Posts
One relay no matter how many pumps. If it was getting power elsewhere, it never would have run rough.

What's the temperature up there? If it's fairly warm, then it was probably vapor pressure in the tank that was pushing the fuel up. Fords will run on VERY little pressure (though not very well under a load) compared to GM & Dodge.

A nearly-empty tank will also generate significant vapor pressure because a little slosh REALLY increases the fuel's surface area. How much is in yours?
I gotta question for you, and it kind of relates to this.

A friend and i got into a discussion about fuel pumps and the amount of gas you keep in your tank. Seeing that gas prices are phenomenal around here, i fill up as needed, but rarely have anything more than a half tank.

He on the other hand, never lets his drop below a half a tank. He jumped into my Bronco and started yelling that i was going to blow my fuel pump up because i was running with less than a quarter tank. I went ahead and told him that i rarely have more than a quarter tank, and never have more than a half, and three quarters to me is full.

His theory was that the lack of gas will cause the fuel pump to fail. The fuel pump is cooled by the fuel, and when you run it near empty it gets so hot that it's more prone to failure.

I told him if that was truth, my pump would have failed years ago (knock on wood), that i run my tank to "E" and then fill it and i have run it for days at a time, well below one quarter of a tank and have yet to have my fuel pump "blow up" which would be quite a spectacular event. The fuel pump really doesn't care how much fuel is in the tank, it's going to pump irregardless until it can't pump anymore. However if there is crap in the bottom of your tank, you have the potential to clog your filter.

So my question to you is, who is right? Does the fuel pump actually care how much fuel is in the tank?
 

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Satyr of the Midwest
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No.
 

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penis
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So my question to you is, who is right? Does the fuel pump actually care how much fuel is in the tank?
The intank pump is insulated and is cooled as fuel passes through it that and since it sits in the bottom of the tank well below the 1/4 tank mark it is cover with gas. Yes the fuel pump cares on how much fuel is in the tank once it is all gone it will stop working. May run on vapor for a day or two.
 

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Practicing Infidel
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15,299 Posts
Discussion Starter · #14 ·
One relay no matter how many pumps. If it was getting power elsewhere, it never would have run rough.

What's the temperature up there? If it's fairly warm, then it was probably vapor pressure in the tank that was pushing the fuel up. Fords will run on VERY little pressure (though not very well under a load) compared to GM & Dodge.

A nearly-empty tank will also generate significant vapor pressure because a little slosh REALLY increases the fuel's surface area. How much is in yours?
Temps were up there Steve

High 80s, in the sun on the hot tarmac driveway. Other conditions that fit the theory are a pile of sloshing as the side road is really a side lawn/path. Also it didn't take me more than a minute to get from front to back and parked.

Tank was just about half or slightly below as the trip meter was about 230 miles (my gauge only reads the top half of the tank, when it reads empty, there's really half a tank left in there{yes I've checked many times}).

Thanks

Sixlitre

p.s./
SJBronco these unicorns sound like a renewable resource. Next time they show up I'm gonna see baout getting some bridles onto them:toothless

I figure if I harness about 200 of them horned horses I'll be drivin' fer free !
 
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