Rick's Free Auto Repair Advice

A bad battery can cause misfires

A bad battery can cause misfires and all kinds of other performance issues

The power requirements on older cars was quite low. The ignition and fuel system didn’t draw much power. But it’s a whole different story on newer cars. A C.O.P. ignition system, for example, uses up to 6-amps per coil at highway speeds (4 cylinder engine = 24-amps). The fuel injectors use 4-6-amps each. The electric fuel pumps use up to 12-amps. And that doesn’t even count the power used by the ECM, ABS, electric power steering, radiator fan, or even accessories. If your charging and battery system aren’t working properly, a bad battery can cause misfires and all sorts of other operating problems.

How a bad battery can cause misfires

Fuel Delivery Issues:

The fuel pump, which is responsible for delivering fuel from

low pressure fuel pump

Low pressure fuel pump

the tank to the engine, relies on electrical power. A weak battery might not provide sufficient power to the fuel pump, leading to inadequate fuel delivery. Insufficient fuel supply can result in a lean air-fuel mixture, causing misfires.

• Low power to fuel injectors — This is especially troublesome on direct injection vehicles. This would cause a lean fuel mixture.

Inadequate Spark Energy:

Low primary current to the ignition coils — If voltage/current is low, then firing voltage is also low and that causes misfires.

Electrical System Instability:

A weak battery can lead to an unstable electrical system, affecting the overall performance of various components.
Electronic control units (ECUs) that manage engine functions may not operate optimally, leading to misfires as the engine struggles to maintain proper timing and fuel-air ratios.

Sensor issues — The MAF sensor has a heated element that requires power and oxygen sensors have internal heaters that require power. If power/voltage is low, it can affect their readings which can affect the air/fuel mixture.

©, 2022 Rick Muscoplat


Posted on by Rick Muscoplat

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