Modern cars feature a wide array of electrical and electronic parts to enhance their performance and your driving experience. However, their increasing dependence on electrical equipment renders them more vulnerable to electrical interference. In particular, EMI and RFI can cause issues with parts like the radio, instrument gauges, and even the powertrain control module. Knowing about EMI and RFI will help you better understand how to protect your vehicle from them.
EMI stands for electromagnetic interference. The term refers to a disturbance in an electrical circuit or path that disrupts the performance of electronics and electrical equipment.
EMI originates from an electromagnetic field (EMF), an area of invisible energy created by electricity and magnetism. EMFs can be natural or artificial. Natural causes of EMFs include lightning and static electricity. Examples of artificial EMF generators include cell towers, magnets, and radio towers.
RFI is short for radio frequency interference. It is an electrical disturbance caused by radio waves. Radio waves are a type of electromagnetic wave, making RFI a subset of EMI.
Some people use EMI and RFI interchangeably. However, RFI specifically applies to radio-based electromagnetic interference. While all RFI count as EMI, not all EMI can be considered RFI.
EMI and RFI disrupt the operation of electronic components. Digital gauges and displays might show inaccurate readings, operate erratically, or stop working altogether.
EMF generated by a partially shorted cooling fan motor in a vehicle engine compartment can create EMF that will saturate nearby wire harnesses with induced current that can dreadfully confuse the fuel injection system into doing very strange things. Bad cooling fan motors may pull more current without blowing the fuse and create EMF that will literally cause the engine to stall, misfire intermittently, lose power, etc.
Radios might work intermittently, and you’ll hear static in the speakers. In the worst-case scenario, the PCM might malfunction when exposed to intense EMI, leading to severe issues that affect how your vehicle performs on the road.
It might seem impossible to regulate EMI and RFI in your vehicle. After all, many things inside and outside your car or truck generate EMFs. However, there are ways to minimize EMI and RFI in critical car parts, such as the spark plugs.
Try the following approaches to improve EMI and RFI control in your vehicle:
Adding a ground strap to your vehicle is one of the easiest ways to prevent EMI. The ground strap is a metal strip that connects the engine with the chassis or negative battery terminal. Usually made of copper brazed with tin, the strap provides a common ground for every electrical part grounded to the engine block.
The ground strap helps prevent EMI by safely directing electrical current into the ground. It prevents the current from reaching places it shouldn’t go.
If your vehicle has a ground strap, inspect it regularly. Replace a damaged strap to keep your car or truck grounded
Spark plugs are a significant source of EMI. When a high-voltage spark leaps from the plug to the combustion chamber, it generates high-frequency electromagnetic waves. The EM waves are strong enough to cause electromagnetic interference in parts far from the spark plugs, such as the PCM and radio.
That being said, resistor plugs aren’t a good idea for every modern vehicle. For example, 1997 Explorers with 4.0L SOHC engines came from the factory with resistor spark plugs but the resistor plugs all had to be replaced on those engine platforms under a special program Ford issued because of too many issues with misfires.
Aside from installing resistor spark plugs, you can further reduce EMI by repairing or replacing bad spark plug wires or bad COP coils.
You can even reposition the spark plug wires to increase the distance between them and parts that might accidentally transmit their current and accompanying EMI elsewhere.
Two spark plug wires that are next to each other on the cap and fire adjacent cylinders should be separated in the plug harness loom by other wires. Examples of this would be older Chevy and Ford V8s. The firing order on an older Chevy V8 is 18436572.
Plug wires 5 and 7 are next to each other on the cap and cylinders 5 and 7 also are next to each other on the driver side bank of the engine where the odd numbered (1-3-5-7 on the driver side bank).
Spark plug wires carry high-voltage current to the spark plugs. Thick insulation covers the length of each wire, keeping the powerful current in the wire until it reaches the spark plug, but again, one plug wire can induce voltage in adjacent wires, including computer cam and crank sensor wires.
Further, damaged insulation exposes part of the wire, allowing the electric current to escape. When the powerful current jumps out of the wire, its strong magnetic field creates significant EMI.
Each end of the spark plug wire also features a rubber boot that keeps contaminants out of the wire, but when the wire is compromised at its terminal, ozone is created by the naked spark and causes issues with corroding the aluminum terminals at the cap or the coil tower.
If you find warning signs of EMI or RFI, check the spark plug wires for damaged insulation or boots. Afterward, examine the ignition wires and coils. Look for loose connections and damaged insulator jackets that allow electric currents to leak out of the wire or electrical part.
Are you installing an electrical part or component? Coat its connector with dielectric grease before plugging or screwing it in.
Dielectric grease is a viscous lubricant that keeps water out and insulates against electricity.
A spark plug terminal that is snapped dry (without dielectric grease) onto the plug tower can have micro-sparks that cause RFI. Since dielectric grease is an insulator, it prevents naked sparks by forcing the spark voltage to only travel from the terminal to the plug tower where the metal is actually touching rather than having a lot of little RFI-creating sparks. Dielectric grease also prevents moisture and mitigates the unpleasant “vulcanizing” of the plug boot against the ceramic of the plug, which makes it very difficult to remove.
Once applied to electrical connections, the grease coating serves as a protective layer against corrosion and contaminants.
A coat of dielectric grease keeps electrical parts and components like battery terminals, lightbulbs, and spark plug boots safe. It seals the connection and keeps moisture and contaminants out of the part. It also lubricates the surfaces of the connections, preventing direct metal-on-metal contact while allowing electric current to flow through it.
Like resistors, dielectric grease also has high resistance. The grease can reduce EMI by decreasing the voltage of the electric current passing through it.
Before applying dielectric grease, ensure the part fits tightly. Otherwise, electricity can still escape through the loose connection.
Last, you can use ferrite beads to protect individual electrical and electronic parts from EMI and RFI. Ferrite beads are a passive low-pass filter that increases the resistance of the wire to the electric current. The beads either send the high-frequency signals back up the cable or dissipate the electromagnetic energy as heat.
While you cannot eliminate all sources of EMI and RFI in your car, you can keep them within acceptable levels. Carefully check your vehicle’s electrical components for any signs of trouble and take the appropriate steps to mitigate electromagnetic disturbance.
Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.