Tune-Ups: Spark Plugs, Fuel Injectors and Timing Belts

The definition of engine “Tune-up” has changed significantly with technological advances.   On older engines, setting the idle speed, fuel/air mixture, carburetor balance, spark plug and distributor point gaps, and ignition timing were regular “tune up” maintenance. On modern engines, equipped with electronic ignition and fuel injection, some or all of these tasks are automated, making a “tune up” on these vehicles as little as periodic fuel injector cleaning and changing spark plugs and wires.

Understanding when tune-ups are necessary and what is included in each tune up is essential for proper car maintenance and as noted above, can vary significantly based on the vehicle, so refer to your owner’s manual for guidance.  Newer model cars with electronic ignition will have typical preventive maintenance issues such as replacing filters, brake pads, engine belts, etc. being handled via routine “oil change/tire rotation” procedures and may only require a “tune up” of new spark plugs and wires every 100,000 miles.  Therefore it is important to have regular preventive maintenance and oil changes performed by experience technicians that will assess other maintenance issues based on your vehicle OEM recommendations.

Spark Plugs

Worn or damaged spark plugs can lead to a number of engine problems.  Misfires, hard starts, increased emissions, and poor fuel economy are all signs of possible spark plug issues.  Spark plugs should be replaced every 30,000 – 100,000 miles and be sure to check your owner’s manual for information specific to your automobile. You can replace them yourself or have an auto technician do it for you.  They are generally accessible but may be hard to reach without special tools. 

Spark Plug Wires

When replacing spark plugs it is common to replace the spark plug wires as well.  Whether you replace the spark plug wires or not, it is vitally important to label them so you know exactly which wire goes with which spark plug.  If you put the spark plug wires back in the wrong order, your car will not run efficiently. 

Fuel Injectors

If your vehicle is having hesitation, emission or performance problems, you may be having a fuel injector issue which can be caused by a buildup of fuel varnish deposits on the injectors. This reduces the amount of fuel that the injector sprays, which in turn may cause the engine to run lean and misfire, hesitate or stall.

A fuel injector is nothing more than spray nozzle. With mechanical injectors, a spring loaded valve allows fuel to squirt out of the nozzle when line pressure overcomes spring tension that holds the valve shut. With electronic injectors, a spring-loaded solenoid pulls open a pintle valve or ball type valve when the injector is energized by the car’s computer. This allows the pressurized fuel in the fuel rail to flow through the injector and squirt out the nozzle and into the engine.

Problems can occur even with a slight buildup of deposits. Because the injector orifice is so small, it doesn't take much crud to restrict the flow of fuel or to disrupt the spray pattern. For good combustion, the injectors must produce a fine cone-shaped mist of fuel vapor. Wear or deposits in the nozzle can create "streamers" of liquid fuel that vaporize and burn poorly. This, in turn, can cause hesitation, emissions and performance problems.

If you have fuel injector symptoms as noted above, injector cleaning can be done by a car care professional or there are do-it-yourself solutions available.  However, professional cleaning will generally provide longer lasting relief. 

Timing Belt – a high mileage vehicle issue you should know about 

One of the greatest dangers to high mileage cars is also one of the least well known. While we expect and try to prevent cases of engine or transmission failure with periodic preventive maintenance, the death of many older or high mileage cars is nothing other than a failure of the timing belt.  The timing belt is essential to your car’s engine as it runs around the camshaft and assists in allowing air into the engine and releasing exhaust from the engine.  An engine will not run without the timing belt.  If the timing belt fails, your engine will suddenly stop and it can be a catastrophic failure destroying the engine.  This is one area that you should refer to your owner’s manual on as recommended replacement intervals can vary widely.  However, a general rule of thumb is to get your timing belt replaced every 60,000 – 75,000 miles, however some OEM’s recommend changing at 100,000 miles.  The replacement should be done by a certified mechanic and costs can vary widely depending on the vehicle and what needs to be removed to get to the timing belt.  Many estimates can range from $250 - $750 but can go much higher so get several quotes.
Don't be intimidated by an auto service technician that is "trying to SELL you a service". 

Prepare and educate yourself to have an informed discussion at the Auto Service Shop.

Click here to learn more!