These days the word tune-up is still being used, but it is not actually what is happening . Yet many people think their engine still needs a tune-up. What they actually need is preventive maintenance. Or, if their Check Engine Light is on, what they need is a diagnostic scan to examine what is causing the fault. The same is true if their engine is hard to start, stalls, runs rough, gets poor fuel mileage, doesn’t run right, or is experiencing any other kind of driveability or emissions problem.
The only engines that still need a tune-up today are old ones from the 1970s and back with carburetors and distributors. These engines do not have computers that automatically make adjustments to timing and so forth.
No Definition for a Tune-Up
There’s no common definition of what precisely a tune-up should include, but most would agree that it involves replacing the spark plugs and performing other adjustments 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. In the past your average home mechanics had all the tools needed in thier tool boxes, but now this isn’t the case. 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 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 would be 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). This tool should be in every technician’s toolbox and if your mechanic says he doesn’t have this tool then you need to go to a different mechanic. 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).
THE 100,000 MILE “NO TUNE-UP” MYTH
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.
Regular oil and filter changes are still necessary to maintain proper engine lubrication. Most experts still recommend changing the oil and filter 3,000 miles or three to six months. The oil change interval can be stretched out to reduce maintenance costs if a vehicle is driven under ideal conditions (no extremely hot or cold weather, no short trip, stop-and-go driving, no excessive idling, no extremely dusty road conditions, no trailer towing, no turbocharging). But the average driver is more often than not a “severe service” driver so should follow the 3,000 mile change interval.
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. Such a filter might go 100,000 miles. Then again, it might not. A couple of tanks of bad gas or some erosion caused by accumulated moisture can cut short the life of any filter, even a so-called lifetime filter. Sooner or later even a lifetime fuel filter will have to be replaced.
As for air filters, the service life depends more on environmental factors rather than 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 also needs to be replaced at specific intervals (see your owners manual for the location and recommended service interval).
Repairs are also inevitable regardless of what the tune-up interval is supposed to be. It’s pretty unlikely that a set of front disc brake pads will go 100,000 miles in city driving — 20,000 to 30,000 miles is a more realistic figure. The same goes for belts, hoses, the battery, water pump, exhaust system and many other parts. No vehicle that’s yet been built can even come close to going 100,000 miles without needing some type of maintenance or repair.
THE 60,000 MILE MAJOR TUNE-UP
Many import dealers promote a 60,000 mile major tune-up that includes a long list of items they supposedly check, and may also include normal tune-up replacement parts such as spark plugs and filters. They may also do a coolant flush, transmission flush and/or brake fluid flush. The service is fairly expensive ($250 to $1000 or more!), and is likely unnecessary provided you have changed your oil regularly, you have kept your fluid levels full, and the engine is not experiencing any problems. I think people who spend this kind of money to have their engine examined should also have their head examined. But if you want to pay for a “piece-of-mind” check-up, your new car dealer will be more than happy to accommodate you.