I have a 2008 Accent and it has 150,000 miles on it. Recently the car gives me problem when I try to start and has to pump gas to get it started. The spark plugs look ok. The battery was weak and so I replaced it but it still gives me problem. If I keep the car shut for say 5 minutes (when I shut it off at the gas station to fill gas), it gives me problem starting. If I shut the engine for longer time (15 minutes or longer) then it is ok. Can you suggest, what maybe wrong.
My best guess is that you have leaking fuel injectors.
Leaky injectors is probably the cause. You can try running a large bottle of Techron in a full tank of gas.
I don’t think “pumping the gas” is the best approach. Next time, just floor the gas pedal before starting. This shuts off the injectors to let you clear a flooded engine. If this helps, it also points to leaking injectors.
I too support the injector theory.
Pumping the gas (or, even better, holding the pedal down) provides an opportunity for a larger volume of air to move through the induction system to clear excess fuel in the cylinders. Letting it sit for a time also allows fuel in the cylinders to disperse through evaporation. My theory is that when you shut the engine off for a short time, like to fill the tank, leaky injectors are allowing the pressurized fuel in the lines to get into the cylinders as the line pressure drops. Fuel lines on modern cars are typically 40psi or higher. But that creates a “flooded” condition, which needs to be cleared via the allowance of high volumes of air, which the pumping accomplishes. It would work even better to keep the pedal down for a few seconds while the engine cranks.