Here Are The Signs Of A Bad Fuel Pump

Most people never think of their cars' fuel pumps until they fail, but they actually play a major role in moving you around: If gasoline is your vehicle's lifeblood, the fuel pump is its beating heart. With that in mind, a failing fuel pump can be flat-out fatal to your ride if it's not caught early. The good news is that a faulty pump can often let you know when it's nearing the end of its usable lifetime, and it does so in two basic ways. 

The obvious one is that it can prevent enough gasoline from getting to your engine, reducing power and leading to problems starting the car, difficulty accelerating or maintaining a steady speed, and hearing assorted disturbing noises from under the hood. These can range from backfires to popping and coughing, and they are all sounds your motor makes when it is struggling with a lean air-fuel mixture. Of course, another way you can know when a fuel pump is faulty is that the check engine light may come on — and return after you've cleared it.

Yet some fuel pump problems create the opposite situation, where your engine gets too much fuel. A case in point would be an issue with the pump's fuel pressure sensor. Now you may be dealing with a rich air-fuel mixture that can cause sudden spikes in speed or engine revs, as well as a sudden drop in fuel economy as the excess fuel goes to waste. Needless to say, if your fuel pump stops working entirely, so will your engine.

To be clear, we're focusing on the modern electric fuel pumps found in nearly all new vehicles sold today. There's nothing tricky about how these work, since they're literally electric pumps that, well, pump the fuel from the tank to the engine. What controls them, though, is a little more sophisticated. They're tied in with a fuel pump control module, which regulates their pressure based on signals from the ECU, which, in turn, are based on the demands from the engine. The result is that the more work the engine is being asked to do, the longer the fuel pump will run in a given scenario.

However, before Bosch introduced electric fuel pumps in 1966, the pumps operated mechanically by running off the engine's camshaft. As the cam lobes rotate, they push against an activating rod connected to a diaphragm, moving the diaphragm back and forth. When the diaphragm is drawn back, it creates a vacuum that's used to suck fuel from the tank -– think of a doctor pulling back the plunger of a syringe to get medicine into it. Anyway, a notable drawback of these systems is that a mechanical fuel pump only changes speed as the engine rpm changes. Meanwhile, before mechanical pumps made the scene, most cars didn't have fuel pumps at all. They had fuel tanks mounted above the level of the motor, which allowed gravity to work its magic. Unfortunately, this often meant storing highly flammable gasoline fairly close to the hot engine — a sometimes explosive combination.

Fuel pumps are relatively robust components that can easily last more than 100,000 miles. This means a lot of drivers may never have to worry about fuel-pump problems at all. But they don't last that long by accident. Many of the most common reasons for fuel pump failure can be avoided by following a few tips. One of the most important is to never let your gas tank get below a ¼ full. The issue here is that modern electric fuel pumps are actually located right in the tank, and they rely on the surrounding gasoline for coolant and lubrication. Without enough, then, the pump is at risk of overheating. Knowing how often to change your fuel filter can also make a difference. After all, a clogged filter makes the pump work harder to force the fuel through, again raising the risk of overheating. The stuff capable of clogging your filter can clog the pump, too, as any contaminants in the gas would have to go through the pump first to get to the filter.

All that said — and despite their potential to last 100K miles — fuel pumps can simply wear out through regular use. Nor can they usually be repaired. Most experts recommend a complete replacement if your fuel pump is going bad. For one thing, a single pump is made of many smaller, complex, and interdependent parts, and a problem with one of them can immediately put damaging stress on the others. In fact, they're often engineered from the start to be replaced as a single unit — with costs on modern cars typically running $1,000 to $1,300.