To diagnose a weak pump, start your car and listen for three things: 1. the relative rate at which the engine plays (too fast) to cold-start or run smoothly; One symptom of a weak fuel pump is its inability to provide enough pressure for the appropriate amount of fuel at the injectors. Most vehicles are designed to start with a fuel pressure between 40 and 60 psi. Conversely, a low-pressure pump that is only good for 30 psi will produce long crank times or no-starter at all. Using a fuel pressure gauge to check fuel pressure can confirm poor pump performance.
A sluggish throttle or sputtering when driving at freeway speeds can be another symptom of a worn out fuel pump. During acceleration, the engine demands more fuel, and as such the load on fuel pump increases in order for it to continuously provide fuel. When the pump is unable to produce enough, the engine could cough or hesitate. But a reduction in fuel flow of just 15 per cent can have a discernible effect on performance – particularly when it comes time to overtake or tackle the hills. For instance, in 2016 there was a recall issued for cars suffering fuel delivery issues thanks to faulty pumps which led to stalling and hesitation under load.
Another diagnostic step is testing the voltage of your fuel pump. The 12 volt supply to the pump needs to be reliable. You can measure the voltage with a multimer at the pump electrical connectors. If the voltage falls below 12 volts, power to the pump may be compromised; if it is correct but the pump remains weak, then internal components of the pump may be failing. A pump that draws only 4 amps instead of the normal 6, for example, is a weak pump that will produce insufficient pressure for effective fuel delivery.
A weak pump also effects fuel efficiency. The engine will compensate for the lack of power by running lean, and use more fuel. Decreased gas mileage by as much as 10-20 percent — could mean that the pump is not working at full capacity. Fuel consumption will gradually decline with pump degradation. Checking regularly could highlight this problem so you know to replace it in time.
Finally, one more low-tech way to diagnose a problem is to listen for unusual sounds. A properly functioning fuel pump should operate nearly silently, but a weak or failing one will make an unhealthy whining or buzzing noise. This noise is often exacerbated by low fuel, as the pump will work harder to move sufficient fuel flow. Noisy fuel pumps are hardly new in various vehicle recalls; it's worth noting for context that a bad pump caused breakdowns from inadequate fuel pressure in 2018.
Visit Fuel Pump for further advice on how to diagnose a Fuel Pump problem.