Fuel System Issue
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4wd Low
Joined: Jun 2023
Posts: 13
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Fuel System Issue
Hi, I have a 1990 F150 standard cab with a 4.9. I was running my truck the other day and the rear tank started overflowing at the cap. Both tanks have new fuel pumps and lines that are two years old. I ended removing the rear tank because I wanted to replace it anyway and while I was running the truck with the front take fuel was squirting out of one of the lines that went to the rear tank. I capped it off and am just running the front tank until I buy a new rear one. My gas gauge also stopped working. Is there a reason why my truck is sending fuel from the front tank to the rear tank while I’m running the front tank? Do both tanks have to be connected for the gauge to work? Thanks for the help.
Hotshot
Joined: Jun 2015
Posts: 12,871
Likes: 2,445
I’d say the check valve in both pumps went bad. You don’t have it capped off correctly? No, each fuel delivery module has its own fuel sending unit. What is it doing? Is it reading empty, full or is it stuck somewhere in between?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Yes, the very common crossflow issue is caused by a bad check or shuttle valve in the rear fuel delivery module (for your scenario). Aftermarket versions tend to have a short life.
Fuel tank selector diagram for your 1990 model year gas engine truck.
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4wd Low
Joined: Jun 2023
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It will read around a quarter tank sometimes and past full at other times, but mostly stays at a quarter. Thanks for your response.
Hotshot
Joined: Jun 2015
Posts: 12,871
Likes: 2,445
I am thinking the rear pump check valve went bad. You removed the pump but didn’t plug the lines good enough for the amount of pressure. The sending unit in the front pump is now failing but don’t take my word for it. Rla is much more knowledgeable about this problem than I am.
Tuned
Joined: Feb 2022
Posts: 301
Likes: 30
From: Perth Ontario
Bad check valve in rear pump. I bought a new cheap pump from rockauto. It was a ultra pro or ultra power something like that and it was bad right out of the box. I read a couple weeks ago on hear that same pump and same thing happened to another guy. I put a Delphi pumps in. Hopefully I won't have to worry about them again. The cheap pumps would probably be ok if you only had one tank but there no good with dual tanks.
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4wd Low
Joined: Jun 2023
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Don’t think I’m dumb, but what is that? I’ve been working on my truck for awhile now and research before I do anything, but I don’t recognize that part.
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4wd Low
Joined: Jun 2023
Posts: 13
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Thank you. Where do I place the valve as far as location on the line?
Hotshot
Joined: Jun 2015
Posts: 12,871
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4wd Low
Joined: Jun 2023
Posts: 13
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Hotshot
Joined: Jul 2020
Posts: 10,533
Likes: 2,661
From: Near Salt Lake City
The fuel check valves issue was a recall
2 recalls in fact and affects 90-93 full size trucks
93S68 was the second one (I believe) where the fuel pressure regulator was also replaced.
2 recalls in fact and affects 90-93 full size trucks
93S68 was the second one (I believe) where the fuel pressure regulator was also replaced.
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4wd Low
Joined: Jun 2023
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I’m assuming it’s a little too late to get them fixed at the dealership. LOL.
Mountain Pass
Joined: May 2019
Posts: 204
Likes: 10
If it was a TSB, yes. A recall is forever until it is fixed. My 96 had the cruise control recall done in 2017 or 2018.
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