Bump it back and forth
If it is jammed with grit, I think the best way to loosen it would be to jog it backwards by reversing polarity very intermittently. Flush with WD40 or similar, use a carefully controlled compressed air blowgun, and cycle back and forth by changing polarity.
Pump probably has a built in check valve for one way direction only, so if you run backwards for more than a brief moment, damage due to cavitation or other might occur.
Remove and get it on a bench so you have better control over this potentially dangerous procedure. You don't want to be stuck underneath your car with petrol, atomized solvents and 12vdc sparks. Safety glasses are always a good idea.
If it is jammed with grit, I think the best way to loosen it would be to jog it backwards by reversing polarity very intermittently. Flush with WD40 or similar, use a carefully controlled compressed air blowgun, and cycle back and forth by changing polarity.
Pump probably has a built in check valve for one way direction only, so if you run backwards for more than a brief moment, damage due to cavitation or other might occur.
Remove and get it on a bench so you have better control over this potentially dangerous procedure. You don't want to be stuck underneath your car with petrol, atomized solvents and 12vdc sparks. Safety glasses are always a good idea.