Although many people still hold the opinion that the engine needs a tune-up, actually, what is needed is preventive maintenance. And when the problem arises, what you need is using a diagnostic tool to determine the problem cause. The only engine that still needs a tune-up is one from the early 1980s and has carburetors and distributors.
Tune-Up Definition is Undefined
There’s no common definition of what exactly a tune-up should include, but most would 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. The problem is there is almost nothing that can adjusted or “tuned” under the hood on late model engines with computerized engine controls. Ignition timing is fixed and controlled by the engine computer, as is idle speed and the fuel mixture. Base timing can be checked with a scan tool, but cannot be adjusted on most engines. The same goes for idle speed 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.
A simple maintenance type tune-up (a new set of plugs) may make an 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 problem is due to something else, 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.
TUNE-UP CHECKS
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):
*Battery voltage
*Charging voltage
*Power balance or dynamic compression (to identify any mechanical problems such as leaky exhaust valves, worn rings, bad head gasket, bad cam, etc. that could adversely affect compression and engine performance)
*Engine vacuum (to detect air leaks as well as exhaust restrictions)
*Operation of the fuel feedback control loop (to confirm that the system goes into closed loop operation when the engine warms up)
*Check exhaust emissions (this should be a must in any area that has an emissions testing program to confirm the vehicle’s ability to meet the applicable clean air standards, and to detect gross fuel, ignition or emission problems that require attention)
*Verify idle speed (should be checked even if computer controlled to detect possible ISC motor problems); Idle mixture (older carbureted engines only, but injector dwell can be checked on newer vehicles to confirm proper feedback fuel control)
*Check ignition timing — if possible (should be checked even if it is not adjustable to detect possible computer or sensor problems)
*Operation of the EGR valve.
OTHER CHECKS
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:
*Spark plugs (gapped to the correct specs, of course). Consider long life platinum or iridium spark plugs on applications where plug accessibility is difficult or where longer service life may be beneficial
*Rotor and/or distributor cap (if required)
*Fuel filter; Air filter; PCV valve and breather filter
*Other parts on an “as needed” basis (things like spark plug wires, belts, hoses, fluids, etc.)
*Check and adjust (if required on older vehicles) ignition timing, idle speed and idle mixture; O2 sensor(s).
OXYGEN SENSORS
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.
So does that mean the oxygen sensors should be replaced as part of a tune-up? Not unless they are defective or are acting very sluggish. 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. 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 are not something you want to replace unless it is absolutely necessary.
Some manufacturers do recommend replacing oxygen sensors for preventive maintenance, however. 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 mile intervals.
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.
The cure is to clean the injectors and 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.
Is engine tune-up really outdated?
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