Why does the gas pump’s auto-shut off activate before my vehicle is filled?

When filling the truck with gas the auto-shut off will not stay on.
The fuel does not go down like it should.
I could not find any blockage in the hose when I removed them.
Any help will be great. Thank you.


Answer:
We have had several reports of this problem. Reports of this situation apply to the full range of vehicle manufacturers.
The problem results from the controlled filler necks mandated on all vehicles including light trucks, SUVs, and cars. In order to meet anti-pollution guidelines, control gasoline fumes and internal overflows, there are EPA mandated filler neck specifications. These specifications make filler necks more restrictive than they were in the “old days”.
Restrictive flow through the filler necks puts limits on the rate of flow.
Consider gasoline pumps: These devices have automatic safety shut-off valves in the handles to prevent overflow when the vehicle’s tank is full and prevent uncontrolled flow if the pump’s handle were to be locked in the “on” position and fall out of the filler neck.
These situations combine to create a delicate balance between the flow pressure of the gasoline, the speed gasoline can flow through the vehicle’s neck, and the sensitivity of the automatic shut-off valve in the pump handle.
When the situation described in the above question occurs, it indicates that the rate of gasoline flow from the pump exceeded what was allowed by shape and specification of the vehicle’s filler neck.
A solution is to “hand-meter” the pump handle to try to ensure that gasoline does not flow too quickly for your vehicle’s filler neck.
Another solution is to locate a gas station where the pumps are set to flow somewhat slower when the handle is turned on. This will may mean the gasoline will flow down the filler neck faster than the pump supplies gasoline. This situation will prevent the auto shut-off valve from being triggered.
Also, a problem may arise following routine maintenance of gasoline pumps. Sometimes the mechanism is reset to be more sensitive and shut off with less back pressure than it had before. Sometimes following maintenance, gasoline will flow somewhat faster than it had previously. In this case the same vehicle that received a one-stop fill previously, may now start activating the auto shut-off mechanism. To resolve this, find a new pump and / or gas station that works — until it doesn’t.

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