spark plugs for modern vehicles can be a demanding experience for
today’s parts professionals. Not only have spark plug designs changed,
the ignition systems that create the spark have changed as well.
Because modern engines run so well for so long, many customers have
either forgotten or fail to understand the need for periodic spark plug
replacements. For that reason, many spark plug replacements have become
a major repair that often require two or three hours of time and a wide
array of tooling to complete.
illustrate, four years ago I recommended to a regular customer that he
have the spark plugs changed in his Ford Expedition at the recommended
100,000-mile interval. Unfortunately, the engine continued to perform
well and the spark plugs were never replaced as recommended. Last month
at 155,000 miles, the customer reported that his check engine light had
begun flashing and that the engine was losing power. Given the advanced
mileage, it was nearly certain that the spark plugs were seized tightly
into the engine’s aluminum cylinder heads.
first step was to recover a diagnostic trouble code (DTC) from the
powertrain control module’s (PCM’s) diagnostic memory. The only DTC
contained in the memory was a P0303, indicating a misfire on number
three cylinder. The flashing check engine light indicated that the
misfire on number three cylinder was a “type A” misfire that required
immediate attention because, if raw fuel from the misfiring cylinder
was passing into the exhaust gas stream, the catalytic converter would
eventually fail due to overheating.
some exceptions exist, most manufacturers of 1996 and newer vehicles
specify replacing spark plugs at 100,000-mile intervals. The exceptions
might include 30,000-mile intervals on some domestic and import
vehicles and 140,000 intervals on some hybrid vehicles.
a technician becomes involved with a special set of conditions when a
vehicle like our Ford Expedition rolls in with 155,000 miles on the
odometer. Without a doubt, all of the spark plugs will need
replacement, all spark plug wires will be seized to the spark plugs,
and the spark plugs will be seized into the aluminum cylinder head.
SPARK PLUG REPLACEMENT TIPS
selling spark plugs, keep in mind that spark plugs are now designed to
not only last 100,000 miles, but also to be successfully removed at the
same mileage. Unlike the Expedition’s standard original equipment spark
plugs, modern spark plugs are plated with metals that resist seizing to
aluminum cylinder heads.
the real issue in spark plug removal is avoiding tearing the spark plug
threads away from the cylinder head. Although tool manufacturers make
spark plug thread repair kits, the difficulty with repairing threads is
the lack of accessibility to the spark plugs.
is always the key to removing seized spark plugs. Because the spark
plugs now reside in a well drilled about five inches into the cylinder
head, it’s important to blow loose dirt out of the spark plug well with
compressed air before removing the spark plug. As always, safety
glasses should be worn to prevent injuries to the eyes.
soak the spark plug with high-quality penetrating oil and loosen the
spark plug about one-eighth turn to allow the penetrant to soak into
the carbon build-up on the lower spark plug threads. After soaking for
30 minutes, gently alternate between tightening and loosening the spark
plug. If the spark plug still feels tight, apply more penetrant, allow
it to soak as long as necessary and repeat the procedure until the
spark plug frees itself from the cylinder head. These basic suggestions
can save your retail customer the potential cost of removing, repairing
and replacing a cylinder head.
CHOOSING THE RIGHT PLUG
from the professional point of view, it’s far more cost-effective to
install an original equipment (OE) or OE-equivalent spark plug than it
is to risk creating a cylinder misfire or ruin a cylinder head by
installing a cheaper substitute. In today’s market, your customers
might find themselves choosing between a standard spark plug and
various types of more expensive spark plug electrode designs, precious
metal platings and heat ranges.
explain the differences, standard spark plugs are designed to last for
only 30,000 miles in older engines with cast-iron cylinder heads. For
this reason, they don’t need exotic electrode designs and expensive
gold, platinum or iridium platings on the electrodes. In direct
contrast, modern spark plugs are designed to last 100,000 miles.
ease of removal, the threads on modern long-life spark plugs are plated
with nickel and other metals to resist seizing to aluminum cylinder
heads. They also have their electrodes plated with various gold,
platinum and iridium alloys to resist erosion caused by high-combustion
chamber temperatures. And due to the heat transfer capabilities of
their electrodes and insulator designs, modern spark plugs are also
designed to operate under a wider range of combustion chamber
temperatures found in modern engines.
the Ford Expedition uses a distributorless ignition, a “double
platinum” design is required, which means that both the center and
ground electrodes are plated with precious metals. Both electrodes must
be plated because half of the spark plugs fire on negative electrical
polarity and the remainder on positive electrical polarity. Older
engines with distributor ignitions fire on normal polarity can use a
“single platinum” spark plug, which means that only one of the
electrodes is plated. For this reason also, a single-plated spark plug
should never be substituted for a double-plated version.
INSTALLING SPARK PLUGS
prevent cylinder head damage and engine misfires, modern spark plugs
require correct installation techniques. Because contaminants can
conduct high-voltage spark, it’s important to keep the spark plug
insulator free of oil or greasy fingerprints by inserting the spark
plug into a short length of 5/16-inch fuel hose or a dedicated spark
plug holding tool. Before installation, make sure that the spark plug
air gap meets manufacturer’s specifications.
make sure the cylinder head seating surface is free of dirt. Dirt
caught under the spark plug gasket or tapered seat will allow
combustion gases to leak from the cylinder. Always torque a spark plug
to specification. Most modern spark plugs require only about 7 to 15
foot-pounds of torque to ensure correct seating. Excessive torque can
damage the spark plug threads while insufficient torque will cause the
spark plug to overheat and damage the engine.
SELL THE RELATED PARTS
too often, technicians and retail customers forget that spark plug
wires and coil boots wear out along with the spark plugs. After 100,000
miles of hard use, spark plug wire boots tend to stick firmly to spark
plug insulators. For this reason, spark plug wires and boots are often
damaged when they are removed from the spark plug. In addition, spark
plug wires tend to lose their insulating capacity because of
perforations in the wire’s insulation or the wire being soaked with oil
and other solvents. In contrast, coil-on-plug boots tend to develop
carbon tracking or “flashovers” on their inner diameters when a spark
plug wears out. In this case, installing an old boot with a flashover
mark inside will cause the new spark plug to misfire. Most coil-on-plug
boots are replaceable and should, for this reason, be replaced with the
spark plugs. Selling wires and boots is not only good preventive
maintenance, it helps prevent expensive comebacks and definitely helps
restore profits to the bottom line.
COMPLETING THE JOB
that selling spark plugs is only part of any 100,000-mile maintenance
plan. In most cases, the throttle plate should be cleaned of carbon and
sludge by using an aerosol throttle body cleaner designed for the
purpose. Similarly, because the air filter assembly is usually removed
for spark plug replacements, don’t forget that the air filter should be
inspected and, if it’s a high-mileage vehicle, the mass air flow sensor
should be rinsed off with an aerosol mass air flow sensor cleaner
designed for that purpose. Last, don’t forget to recommend replacing
the fuel filter if required. Recommending these services to your retail
or wholesale customers will add value and performance to an otherwise
expensive spark plug replacement.