Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Fuel Metering System
The function of the fuel metering system is deliver the correct amount of fuel to the engine under all operating conditions. Fuel is delivered to each cylinder by the fuel injectors. The fuel injectors are controlled sequentially by the powertrain control module (PCM). The PCM bases the control of the fuel injectors on several important engine parameters. These engine parameters include the following:
The two most important inputs for fuel control are the mass air flow (MAF) sensor and the fuel control heated oxygen sensors (HO2S). The MAF sensor provides the powertrain control module (PCM) with engine air intake quantity, while the fuel control HO2S provides the PCM with exhaust stream oxygen content information. Determining air density is critical to proper air/fuel management. Air density is primarily derived from the MAF sensor input. The MAF sensor measures the air volume and determines the air density. Larger volumes of air and denser air masses require additional fuel. The information from the MAF sensor is used by the PCM in order to modify the fuel injector pulse width.
The PCM modifies the air/fuel mixture by changing the injector pulse width signal sent to the injectors. By constantly measuring the air intake and the exhaust oxygen content and adjusting the injector pulse width, the air fuel ratio is kept very close to the optimal 14.7:1. This is the range at which the three-way catalytic converter (TWC) operates most effectively and at which the emissions of this vehicle are kept to a minimum. The constant tailoring of the air/fuel ratio is based upon feedback from the HO2S and is referred to as closed loop operation.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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