While operating 89F150 4.9. dual tanks, pressure builds in front tank and overflows. What is the cause?
Driving on front tank, pressure builds in front tank and overflows. If you try to remove filler cap it gushes out fuel.
The fuel pump check valve is bad and allowing the other tank to fill it up. Ford had an inline valve that installed at the outlet of the fuel pump to prevent this. The other option is to replace the pumps as assemblies.
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