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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

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Old 11-10-2012, 09:46 AM
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33homerdoodle 33homerdoodle is offline
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Fuel tank vent valve question

1994 F350 460 dual tanks. My front tank float is bad so always reads empty. I run the front tank first until empty and switch to the back. When back is down low Ive noticed the front tank then has some gas in it enough to run several miles. I think I am pushing fuel from the rear into the front when the front is low.

My question is mine only seems to have a fuel pump for each tank and a vent valve on each tank. There is no other valve or switching unit until you get to the pressure regulator at the engine. So is it more likely I have a bad vent in the front tank, a bad fuel pressure regulator pushing fuel back through the return hose or could a weak fuel pump be the culprit?

I have the bed off so everything is easy to reach and I am changing the fuel pumps/floats now anyway because I have no idea how old they are other than they work, just being proactive. If I need to change the vents what are they called other than "vent"?

Thanks
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Old 11-10-2012, 10:05 AM
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As I understand it, the pressure & return lines from each tank are just Tee'd together. The FDM in each tank has all the valving. They have a check valve on the pressure line, and the return line valve is only open when switched to that tank.
Since you're changing out your FDMs, you should be good to go.
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Old 11-10-2012, 10:16 AM
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Tee, yes. FYI, there is no other selector valve in the line. It dawned on me to pull one of the vents and all it appears to do is push into the very top of the tank and allow vapor to bleed off it. I was thinking there was a way to siphon but if your tank is not 100% full there is an air gap between the vent and gas anyway...kind of hard to siphon that way. 10-4 I'll change the pumps and floats and see what happens. Thank you.
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Old 11-10-2012, 11:28 AM
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the way they work is that the pump that is working has a valve in it that opens to let fuel back to that tank, each pump has one, so unless the pump is running the return valve is closed. i have replaced both of my pumps twice in 180,000 miles. found out that if one pump acts up, say the return valve stick open, then i will affect both tanks, in other words if you get a bad pump then replace both. only other thing you could do if one pump was bad is to pinch off that return line so it wont affect the other. but replacing them isnt to bad, first time i removed my bed, second time i was able to lift it and angle it up more on the passengers side to get to both of them. ford OEM pumps lasted 105,000 miles and the aftermarket lasted 75,000. from what ive seen all you need is something small to get stuck in one of the pumps, say in the return or anywhere and your changing them out.
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Old 11-10-2012, 11:28 AM
 
 
 
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