The word Tune-up is an outdated and obsolete term. The need for tune-ups went away in the mid-1980s when fuel injection replaced carburetors and conventional spark plugs were replaced with long life platinum spark plugs. Yet many people think their engine still needs a tune-up.
What is needed is preventive maintenance. Or, if your Check Engine Light is on, what you need is a diagnostic scan to determine what is causing the emissions warning light to come on.
If your engine is hard to start, stalls, runs rough, gets poor fuel mileage, does not run right, or is experiencing any other kind of driveability or emissions problem, you do not need a tune-up. You need a scan tool diagnostic check to find out what's causing the problem.
The only engines that still need a tune-up today are old ones from the early 1980s and back that have carburetors and distributors. Yet the tune-up myth persists, and may people still think it is some kind of "cure-all" for what ails their engine.
To make matters worse, many new car dealers tell their customers they need a 50,000 or 60,000 mile "major" tune-up - which is totally unnecessary. Basically, all they do is inspect your vehicle's fluids and filters, and maybe do an oil change while charging you an inflated price for their "service." Most late model fuel injected engines require nothing more than regular oil changes and an occasional new air filter up to 100,000 miles. At that point, new spark plugs are usually recommended, and possibly a coolant change, new fuel filter and PCV valve). That's all that's needed as long as everything is working normally and the Check Engine light is off. Replacing any sensors (like O2 sensors) should NOT be necessary unless the Check Engine light is on, or there is a driveability or emissions problem.
There's no common definition of what exactly a tune-up includes, but most agree that it involves replacing the spark plugs and performing other adjustments to the idle speed, fuel mixture and spark timing that are necessary to maintain or restore like-new engine performance. On late model vehicles with fuel injection and computer engine controls, there is nothing to adjust or tune because the computer controls ignition timing, idle speed and fuel mixture. Base timing can be checked with a scan tool, but is not adjustable on most engines unless there is a factory software update for the vehicle. The same goes for idle speed, fuel mixture and various emission functions. A scan tool can reveal if the systems are functioning normally, but in most cases no adjustments are possible because the adjustments are programmed into the computer.
Preventive maintenance such as replacing the spark plugs can make a high mileage engine easier to start, improve fuel economy, lower emissions, restore lost pep and power if the old spark plugs are worn or fouled. But if the engine is not running well because of some other issue (such as dirty fuel injectors, low fuel pressure, a faulty sensor, worn piston rings or leaky valves), a new set of plugs alone won't help. A tune-up under these circumstances is a waste of time and money. The engine needs to be diagnosed to find out what is wrong.
An engine check-up should start with a scan for any current, pending or past fault codes. This requires plugging a scan tool or code reader into the vehicle diagnostic connector so the tool can communicate with the powertrain control module (PCM). The onboard diagnostic system does an excellent job of monitoring all the key systems, and on most 1996 and newer vehicles it can even detect engine misfires.
If no faults are found, and the engine is running normally, the check-up is not over because there are additional things that should also be checked (especially if the engine is NOT running normally or any fault codes were found with a scan tool):
In addition to these performance checks, hoses and belts should be visually inspected.
All fluids (oil, coolant, automatic transmission fluid, power steering fluid and brake fluid) should also be inspected to make sure all are at the proper level, and that the appearance and condition of each is acceptable. There should be no sludge in the oil, the ATF should not smell like burnt toast, the coolant should have the proper concentration of antifreeze and not be full of rust or sediment, the brake fluid should be clear and not full of muck, etc.
WHAT TO REPLACE
If the tune-up checks find no major faults, the following items can be replaced for preventive maintenance:
Oxygen sensors on late model vehicles should last 100,000 to 150,000 miles under normal driving and operating conditions (which does NOT include an engine that burns oil, or vehicles that have been under water!). The oxygen sensor is a key sensor that can hurt fuel economy if it is getting old or has failed. One EPA study found that up to 70% of high mileage vehicles that fail an emissions test need a new O2 sensor.
Does this mean O2 sensors should be replaced for preventive maintenance or as part of a high mileage major tune-up? Not unless they are defective or sluggish (slow to respond to rapid changes in the air/fuel mixture). Oxygen sensor performance can be verified with a scan tool, and a bad oxygen sensor will usually set a fault code and turn on the Check Engine Light, but not always. If an oxygen sensor fails or is getting sluggish, it will usually cause the engine to run rich. This causes an increase in fuel consumption and emissions. It usually does not hurt performance or cause other driveability issues.
Oxygen sensors are expensive to replace. They typically cost $35 to $70 each, and some may cost upwards of $200 or more depending on the application. Air/Fuel sensors (basically a more sophisticated type of oxygen sensor) are even more expensive to replace. In addition, V6 and V8 engines have one oxygen sensor for each cylinder bank, and some have two. There are also one or more oxygen sensors in the exhaust system to monitor the catalytic converter(s). So oxygen sensors should NOT be replaced unless there is a valid reason to do so (like poor fuel economy or an emissions problem).
Some manufacturers do recommend replacing high mileage oxygen sensors for preventive maintenance. The recommended replacement interval for unheated 1 or 2 wire wire O2 sensors on 1976 through early 1990s applications is 30,000 to 50,000 miles. Heated 3 and 4-wire O2 sensors on mid-1980s through mid-1990s applications should be changed every 60,000 miles. And on OBD II equipped vehicles (all 1996 and newer), some recommended replacing the oxygen sensors at 100,000 miles to restore like0new performance. Even so, as long as the original sensors are still working properly, there is no need to replace them.
CLEANING FUEL INJECTORS
Dirty fuel injectors are a common problem that can hurt engine performance, fuel economy and emissions. Many experts recommend cleaning the fuel injectors and intake system as part of a tune-up. The need for injector cleaning isn't as great as it once was thanks to improved fuel additives and redesigned injectors. But in areas that have gone to reformulated gasoline, injector clogging is more of an issue.
Fuel varnish deposits that form in injectors restrict fuel delivery, which has a leaning effect on the air/fuel mixture. The result can be lean misfire and a general deterioration in engine performance and responsiveness. Deposits can also build up on the backs of intake valves, causing cold hesitation problems in many engines. Intake valve deposits have been a problem with some newer engines that have Gasoline Direct Injection (GDI).
The cure is to clean the injectors and intake valves. Cleaning is recommended for any engine that is suffering a performance complaint or has more than 50,000 miles on the odometer. Cleaning the throttle body can also help eliminate idle and stalling problems that plague many of today's engines.
The spark plug replacement interval on most late model engines with platinum or iridium spark plugs is 100,000 miles. But that does not mean the engine requires no maintenance whatsoever for 100,000 miles, or that the original spark plugs will go the distance.
Regular oil and filter changes are still necessary to maintain proper engine lubrication. Many experts still recommend changing the oil and filter 3,000 miles or three to six months if a vehicle is used primarily for short trip city stop-and-go driving.
The oil change interval can be stretched to 5,000 miles or longer if a vehicle is used primary for highway driving. For longer oil drain intervals (7,500 miles or more), you should use a top quality synthetic motor oil that can go the distance without breaking down.
The best advice is to follow the vehicle manufacturer's service recommendations in your owners manual. Servicing a vehicle more often than they recommend won't hurt anything, but exceeding their recommendations might result in oil breakdown, sludge formation and expensive engine damage,
Today's 100,000 mile tune-up interval also skirts around the issue of fuel filter and air filter replacement. A number of new cars and trucks now have "lifetime" fuel filters, most of which are located inside the fuel tank with the electric fuel pump module assembly. These filters should last upwards of 100,000 miles -- unless the fuel tank becomes contaminated with dirt, sediment or rust.
The service life of an air filter depends more on environmental factors and exposure to dust and dirt than it does time or mileage. If a vehicle is driven on gravel roads, filter life may only be a few months or few thousand miles.
Many vehicles also have a cabin air filter for the passenger compartment. This filter also needs to be replaced at specific intervals (see your owners manual for the location and recommended service interval). The recommended replacement interval for cabin air filters typically ranges from one to two years, or 15,000 to 30,000 miles.