If you have a problem with the fuel delivery system, it may not always be the fuel pump, relay or filter, though those are the first things that people think of when fuel is not making its way to the engine. The sensors on your vehicle’s engine play a significant part in fuel delivery. The engine requires a certain amount of fuel and everything from air temperature to speed affects fuel delivery. Without the proper air to fuel ration – usually 14.5:1 – the vehicle will not run properly and in many cases, will not run at all.

The Heart Of The System

At the heart of this system is the programmable control module (PCM) or engine control module (ECM), depending on the year, make and model of your vehicle. Certain sensors feed the computer information while others use the information to change the parameter in the fuel delivery system. If something goes wrong with the computer, many things could happen – the vehicle may run poorly, it may not run at all, or it may run well enough that you don’t notice anything wrong except a decrease in fuel mileage.

Sensors That Use Information

Some sensors change how the engine behaves when it receives information from the control module. The idle air sensor, coolant temperature sensor and EGR sensor all change things within the engine and fuel delivery system.

You may notice that some sensors are listed in both categories – that is because in some vehicles they have two purposes. For example, the coolant temperature sensor may not only tell the computer how hot the engine coolant is but may also turn the fan on.

  • Idle Air Sensor (IAC): This is not really a sensor, but a stepper motor. The IAC controls the idle of the engine. For example, when you step on the brake, the RPM drops, but the vehicle does not get enough fuel and air to keep it running. The IAC increases the RPM of the engine, which in turn requests more fuel to keep the engine running. Since the computer sends fuel based on the amount of air going through the engine and there is no air moving at a stop, the engine would stall without the IAC.
  • Coolant Temperature Sensor (CTS): This sensor tells the computer about the temperature of the engine so that it can adjust the fuel mixture, but it also uses the information to turn the fan on via the control module when the engine reaches a certain temperature. Once the fan is on, the engine cools down, and the CTS lets the computer know to adjust the fuel-to-air ratio for the cooler temperature.
  • EGR: The EGR system in newer vehicles is complicated. The EGR sensor tells the computer when the EGR valve opens and how much-unburned oxygen is flowing into the cylinders. The computer uses these parameters to change the injector on time for more or less fuel. The exhaust gas being recirculated cools the cylinders, plus burns any oxygen that was unburned in the first go-around through the engine. This affects fuel delivery system because it changes the engine temperature and amount of air in the engine.

Part 2 of this series talks about sensors with a more direct impact on the fuel delivery system. Before condemning the fuel pump or other parts of the mechanical fuel system, be sure all sensors are working properly, especially if the vehicle is having intermittent problems or using more fuel than it should.