What Causes Fuel Pump Not to Prime?

If the fuel pump relay is not the culprit, and the fuel pump still doesn't prime when turning the key on, it could be that there is a broken wire in the electric motor. In this scenario, it would be necessary to remove the electric motor cover and check for damages or missing wires. If any are found, they will need to be replaced.

If your self priming pump does not prime, there could be many reasons. Replace the check valve. If you have a ball check valve on your discharge line, it may not be functioning properly. The check valve should prevent water from backflowing through the discharge line while the pump is in operation. If the check valve is not functioning properly, fluid may bypass it and continue to circulates through the pump causing it not to prime. Inspect the tubing for kinks or breaks. kinks and breaks can cause air to enter the pump and cause it not to prime. Inspect the output flange for clogs or leaks. A clog or leak at the output flange can prevent fluid from entering the impellers and causing them not to spin, leading to a lack of priming. Replace the pump motor. If your pump runs slowly or doesn’t seem to be pumping as much fluid as it used to, it may be time to replace the pump motor

If the fuel pump relay is activated but the load side switch contact (30 and 87) is not closed, power is supplied to the fuel pump for priming. In the event of a faulty ECM, it may not send pulses to the pump relay so you may notice that the pump isn't priming unless the ECM issue is fixed.

If the fuel pump won't start and you've tried jumping the relay and replacing the fuel pump, your best bet is to have a mechanic diagnose and fix the problem.

Without a working fuel pump, your car will not be able to start. If the pump is failed completely, you may also see smoke or flames coming out of the tailpipe.