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Old 07-07-2011, 06:29 PM   #1
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Default Dual tank problem, what do you think?

Hi, it's 90+ degrees up here so I figured I'd see if someone could steer me the right direction before I went out there to roast. Here's the deal. 1989 F150 dual tanks. It sat for about 4 years before I bought it. Cranked up and ran OK on 4 year old gas though. I was impressed at least. I put some Seafoam in the front tank, changed the fuel filter and it's been running great but when I finally tried the rear tank out, (It was almost empty and I put 20 dollars of new gas in it) it didn't work. It acted like it ran out of gas. Which I'm sure it did, so to speak. I kept trying it every once in a while though and one time it ran for 15-20 miles, then quit. So I put some Heet and fuel injector cleaner and octane booster in it and it worked for a couple of days but then quit again. While I was driving it I might add. But I switched to the front tank and all was well. So what do you think is most likely? Bad switch? Bad pump? What's the best way to check this out?

Thanks in advance!

Oh, anybody got or know the wiring diagram for the switch and pumps?

Last edited by BLS; 07-09-2011 at 04:27 PM.
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Old 07-07-2011, 07:14 PM   #2
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Sounds like the pump to me man. Feel lucky two are still working, yes you have three.
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Old 07-07-2011, 10:46 PM   #3
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Yeah, I thought about that. I just always thought pumps either worked or they didn't. But who knows. Guess for starters the thing to do is check the voltage at the switch. If there's juice and the pumps not running... probably a bad pump. Now I just gotta figure the wiring diagram out. This is supposed to be it. Guess we'll see.

Front tank sending unit: Dark blue-yellow
Rear tank sending unit: Yellow-light blue
Fuel gauge: Yellow-white (or white-yellow)

Switch wires:
outer most (closest to edge of plug): Red
second wire in (next to red): Brown-white

Switch on front tank: Red wire
Switch on rear tank: Brown-white wire
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Old 07-07-2011, 11:44 PM   #4
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Sometimes they put up a fight in the end.
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Old 07-08-2011, 01:18 AM   #5
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It's a long shot but there is a filter in the tank at the pump that can clog. However you have to pull the pump to get to it anyway.
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Old 07-08-2011, 06:57 AM   #6
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Quote:
Originally Posted by BLS View Post
Hi, it's 90+ degrees up here so I figured I'd see if someone could steer me the right direction before I went out there to roast. Here's the deal. 1989 F150 dual tanks. It sat for about 4 years before I bought it. Cranked up and ran OK on 4 year old gas though. I was impressed at least. I put some Seafoam in the front tank, changed the fuel filter and it's been running great but when I finally tried the rear tank out, (It was almost empty and I put 20 dollars of new gas in it) it didn't work. It acted like it ran out of gas. Which I'm sure it did, so to speak. I kept trying it every once in a while though and one time it ran for 15-20 miles, then quit. So I put some Heet and fuel injector cleaner in it and it worked for a couple of days but then quit again. While I was driving it I might add. But I switched to the front tank and all was well. So what do you think is most likely? Bad switch? Bad pump? What's the best way to check this out?

Thanks in advance!

Oh, anybody got or know the wiring diagram for the switch and pumps?
Here is a wiring diagram for my 87, should be the same or very close.
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Dual tank problem, what do you think?-87-duel-tanks.jpg  
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Old 07-08-2011, 06:01 PM   #7
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Here is a wiring diagram for my 87, should be the same or very close.
Hey, thanks!
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Old 07-08-2011, 11:31 PM   #8
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Quote:
Originally Posted by tdcarter72

Here is a wiring diagram for my 87, should be the same or very close.
I have a dual tank on my 95 f150 and I think you have water in your tank, pump your tank out and put newer fuel in it
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Old 07-09-2011, 04:27 PM   #9
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I have a dual tank on my 95 f150 and I think you have water in your tank, pump your tank out and put newer fuel in it
Yeah, I thought of that too. It only had a little fuel left in it and so I put a can of Heet (supposed to get rid of any water) in it, along with some fuel injector cleaner, octane booster and $20 dollars of new gas. I figured I would be able to run the old stuff out of it that way and most of the time it runs really good off that tank. But once in a while it just dies completely. I switch to the other tank and all is well. Then the next time I try the rear tank it's fine... for a while. I agree with Just Call Me Sean that it sounds like a bad fuel pump but... do you still think it's water? I'm not disagreeing with you, just asking.
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Old 07-09-2011, 06:29 PM   #10
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Disconnect the fuel line and use the pump to pump the tank dry, then add fresh gas and try it. If you think it's water.
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