Some things never change, such as the need for periodic
preventive maintenance. But a tune-up is one job that's changed
a great deal over the course of automotive history. The outdated
term is still widely used by many people to describe a service
procedure that's supposed to make an engine run better.
There's no absolute 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 maintain or
restore like-new engine performance. The problem is there's not
much that can adjusted under the hood on many late model
vehicles. Ignition timing is fixed and controlled by the engine
computer, as is idle speed and the fuel mixture. You can still
check base timing (maybe), idle speed and various emission
functions to make sure everything is functioning within factory
specs and are functioning properly. But there really isn't much
of anything left to "tune." Yet motorists still want tune-ups
and believe tune-ups are an important and necessary service.
What most motorists really need when they ask for a tune-up,
though, is something other than preventive maintenance. Unless a
motorist is a rare bird who is actually following the scheduled
maintenance recommendations in his vehicle owner's manual, he's
probably asking for a tune-up because he's experiencing some
kind of driveability problem. His vehicle might be getting hard
to start, not getting the fuel mileage it once did, hesitating
or stalling, knocking or not running with the same zip and power
as before. Or, his vehicle may have failed an emissions test. So
what he probably needs is an engine performance analysis -- and
maybe a new set of spark plugs, too.
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, and so on provided engine
performance deteriorated because of worn or fouled spark plugs.
But if the problem lies elsewhere, a new set of plugs alone
won't do the trick. A "tune-up" under these circumstances would
be a waste of time and money. The first thing you should do,
therefore, when someone asks about a tune-up is to find out why
he thinks he wants one. If he gives any reason other than
scheduled maintenance, he has a performance problem that will
require additional testing to identify the cause (or causes) of
the problem. Only after the performance problem has been
diagnosed should any parts be replaced.
TUNE-UP CHECKS
Any tune-up today should start with a battery of performance
checks to base line or confirm the engine's overall condition.
These should include:
Battery voltage (very important with all of today's
onboard electronics).
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)
Scan for fault codes (to verify no fault codes are
present, or to retrieve any codes that may be present so they
can be diagnosed and eliminated)
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.
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 should be replaced for preventive maintenance:
Spark plugs (gapped to the correct specs, of course).
Consider long life 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).
Spark plugs need to be changed periodically because the
electrodes wear every time a plug fires. When high voltage
current jumps from one electrode to another, it wears away a
little metal from both electrodes. After 45,000 miles of
operation, the plug has fired 60 to 80 million times and wear
has increased the distance between the electrodes. At the same
time, the nice sharp edges on the center electrode have become
rounded and dull. All this increases the voltage required to
jump the gap. If the ignition system can't deliver, the plug may
begin to misfire under load. Accumulated deposits on the plug
tip may also be interfering with reliable ignition. So by the
time the average plug has seen 45,000 miles, it's getting close
to the end of its service life.
Long-life plugs, on the other hand, don't wear as much as
standard plugs. The electrodes are made of tough platinum or
gold-palladium alloys that resist erosion. Such plugs may go
100,000 miles under optimum conditions (no fouling). Of course,
no plug will last anywhere near its potential lifespan if an
engine is burning oil, experiencing abnormal combustion such as
detonation or preignition, or has a fouling problem.
OXYGEN SENSOR
Though most motorists don't even know what an oxygen sensor
is, let alone that their engine may have one or more of these
devices, the fact remains that sluggish O2 sensors cause a lot
of driveability problems. A recent EPA study found that 70% of
all vehicles that fail an I/M 240 emissions test need a new O2
sensor.
To prevent such woes, the O2 sensor can be replaced for
preventive maintenance during a tune-up. Unheated 1 or 2 wire
wire O2 sensors on 1976 through early 1990s applications should
be replaced for preventative maintenance every 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 '96 and newer), the recommended
replacement interval is 100,000 miles.
The O2 sensor is the master switch in the fuel control
feedback loop. The sensor monitors the amount of unburned oxygen
in the exhaust and produces a voltage signal that varies from
about 0.1 volts (lean) to 0.9 volts (rich). The computer uses
the O2 sensor's signal to constantly fine tune and flip-flop the
fuel mixture so the catalytic converter can do its job and clean
the exhaust. If the O2 sensor circuit opens, shorts or goes out
of range, it usually sets a fault code and illuminates the Check
Engine or Malfunction Indicator Lamp. But many an O2 sensor that
is badly degraded will continue to function well enough not to
set a fault code but not well enough to prevent an increase in
emissions and fuel consumption. So the absence of a fault code
or warning lamp doesn't mean the O2 sensor is doing its job.
Deterioration of the O2 sensor can be caused by a variety of
substances that find their way into the exhaust (such as lead,
silicone, sulfur, even oil ash) as well as environmental factors
such as water, splash from road salt, oil and dirt.
A sluggish sensor may not allow the computer to flip-flop the
fuel mixture fast enough to keep emissions within acceptable
limits. A dead sensor will causes the system to go back into
open loop with a fixed, rich fuel mixture. Fuel consumption and
emissions go up, and the converter may suffer damage if it
overheats.
The best way to check O2 sensor performance is with a digital
oscilloscope. A good sensor should produce an oscillating
waveform that flip-flops from near minimum (0.1 to 0.2v) to near
maximum (0.8 to 0.9v). O2 sensors in feedback carburetor
applications have the slowest flip-flop rate (about once per
second at 2500 rpm), those in throttle body injection systems
are somewhat faster (2 to 3 times per second at 2500 rpm), while
multiport injected applications are the fastest (5 to 7 times
per second at 2500 rpm).
When the mixture is made artificially rich by injecting some
propane into the intake manifold, the sensor should respond
almost immediately (within 100 milliseconds) and go to the
maximum (0.9v) reading. Likewise, making the mixture
artificially lean by opening a vacuum line should cause the
sensor's output to drop immediately to the minimum (0.1v)
reading.
OTHER STUFF
Something else that should be part of a tune-up today is
cleaning the fuel injectors and intake system. 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 on
the rise again.
Fuel varnish deposits that form in injectors restrict the
amount of fuel that's delivered with every squirt, 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
should be 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 100,000 MILE "NO TUNE-UP" MYTH
Some would say the auto maker's move to 100,000 mile
"tune-up" intervals on many new vehicles will finally kill the
tune-up as we know it today. Maybe, but what the car makers are
really talking about are 100,000 mile spark plug change
intervals -- which does not include the need for other
maintenance such as oil and filter changes or other repairs that
might be needed during the life of the vehicle.
If the average motorist fails to grasp the true meaning of
today's 100,000 mile tune-up and thinks he can get away with
gas-and-go driving for 100,000 miles without spending a dime on
maintenance or repairs, he'll find out the hard way that lack of
proper maintenance can be very costly. Today's vehicles don't
require as much maintenance as they used to because things such
as idle speed and mixture adjustments, timing adjustments, etc.
have been eliminated. So too has the need for chassis
lubrication thanks to "sealed-for-life" ball joints and tie rod
ends. Many OEM parts are also being built to much higher
standards of durability.
Even so, 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 and air filter replacement, too. 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 corrosion 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.
Does it make sense to replace a lifetime in-tank fuel filter
for preventative maintenance? Maybe -- if one considers what it
costs to have a vehicle towed because of a plugged fuel filter.
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.
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.
