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How Do
I Change My Spark Plugs?
How Do I Change My Spark Plugs?
Introduction
The spark plugs in your engine can give you valuable information about how the
engine
is running. The chemical reaction inside the combustion chamber will leave deposits
on the spark plug that can tell you the condition inside the engine's combustion
chambers. For example: if the engine is running rich all of the spark plugs will
have a black or grey shoot covering the spark plug electrode. If the engine is running
lean all of the spark plugs will be clean and white. If one of the spark plugs looks
way different than the remaining spark plugs the cylinder with the different looking
plug might be having a problem.
WARNING! Always have the vehicle under inspection
on level ground, in park with the emergency brake on. Always wear protective eyewear,
gloves and necessary clothing before inspection or work begins. Never crank an engine
over when anyone is near the battery or engine. Always have a operational fire extinguisher
close by, obey all first aid instructions in the event of an injury. Never stand
in front or behind a vehicle when cranked over or running. When engine is cranked
over keep hands and clothing away from rotating components. Anyone with a heart
pacemaker should not perform this test.
Before You Start:
- Park the car on a flat surface dry surface, engine off, in park with the
emergency brake set
- Gather the proper tools needed to complete the job: Socket wrench (ratchet),
various socket extensions, spark plug socket, spark plug gapping tool, spark
plug thread lubrication (anti-seize, grease), safety eyewear, latex gloves,
hand cleaner and shop towels.
- Allow the engine to cool before spark plugs are removed
- Mark the plug wires with a small piece of tape to identify their positions
in the firing order or cylinder order.
- Confirm your vehicles spark plugs, do not install spark plug that are not
meant for you car. Your car is designed with a predetermined resistance in the
secondary ignition system that if is changed will hinder performance and mileage.
To determine the spark plugs needed consult your owner's manual or a
car repair manual.
Getting Started:
- Step 1 - First, identify the ignition system your car has,
most cars have a DIS (direct ignition system, shown). The HEI (high energy ignition)
this ignition system has a distributor with cap and rotor. The COS system (coil
over spark plug) which has no plug wires just ignition coils. Firmly grab a
hold of the spark plug wire at the boot nearest the spark plug. Gently but firmly
twist the boot to loosen the seal, now remove the spark plug wire.
Removing the Spark Plug Wire
- Step 2 - Remove debris from the spark
plug hole, (canned air works best) then use a socket wrench and spark plug socket
to loosen and remove the spark plug (counter clockwise). Before you remove the
spark plugs, mark the plug wires to identify their positions in the firing order,
this will help to make sure they do not get mixed up. Always use a spark plug
socket to remove the spark plugs. We use a spark plug socket because the inside
of the socket is lined with rubber to help cushion the spark plug insulator,
which is made of porcelain and can be easily cracked or broken removing or installing.
If a spark plug insulator is cracked or broken the engine will misfire as the
ignition spark will travel to the engine block (ground) instead of the spark
plug gap (between the electrodes). Before installing spark plugs always inspect
the spark plug mounting hole threads, check for rust and debris, clean and lubricate
as needed. If spark plug threads are damaged use a thread cleaner or tap loaded
with grease to catch the metal chips that would go into the combustion chamber.
Also use a can of compressed air with the long plastic extension the can comes
with the can and insert into the spark plug hole down into the cylinder and
blow excess partials out (cover your eyes from air-born
debris) to help the removal of additional particles. When removing the
spark plugs organize them according to their related cylinder. Next compare
your spark plugs to those on the chart below for potential or present problems.
Inspect spark plug condition (chart below).
Removing the Spark Plug
- Step 3 - When reinstalling new plugs be
sure the spark plugs your are installing are made for your car and engine size.
Do not install spark plugs just because they fit, design issues can cause internal
engine damage, example: if the spark plug electrode is to long it can damage
the piston. Use a spark plug gapping tool to check the measurement between the
electrodes, most spark plug gaps are between .035 and .045. This gap is important
because it determines the amount of resistance used to "time" the ignition system.
An incorrect spark plug gap will result in low power, poor mileage and possibly
a check engine light notice. For the exact measurement for your car consult
a
car repair manual. Remove the spark plug from the box or container and inspect
the new plug for damage that could have occurred in shipping. A spark plug has
a porcelain isolator that is fragile and can crack easily. Reinstall the spark
plug and install the new spark plug wire. Most of the time a spark plug will
come "pre-set" and ready to install. Continue the process until all spark
plugs and spark plug wires have been replaced. Be sure to use OE (original equipment)
parts for your car or truck to insure the proper performance from your vehicle.
Measuring the Spark Plug Gap
- Step 4 - When reinstalling the new spark plug make sure
the sealing gasket is located on the threaded part of the spark plug, some spark
plugs do not have a sealing ring, this is normal. Only tighten the spark plugs
to "snug" and install a small portion of anti-seize grease to ensure proper
installation. Save the old spark plug in the new spark plug boxes, store them
for future reference. Once you have completed the spark plug change start the
engine and inspect the running condition, it should be smooth with no extra
noises. If your engine is running rough double check the spark plug wires to
make sure one has not popped off or that the plug wires are not in the right
order. If you have double checked your work and the engine still runs rough
please visit -
why does my engine run rough?
Various Spark Plug Conditions:
These spark plug images depict various conditions inside a particular cylinder
or all cylinders and will help troubleshoot the problem.
Normal Condition
An engine's condition can be judged by the appearance of the spark plug's firing
end. If the firing end of a spark plug is brown or light gray, the condition
can be judged to be good and the spark plug is functioning optimally.
Dry and Wet Fouling
Although there are many different cases, if the insulation resistance between
the center electrode and the shell is over 10 ohms, the engine can be started
normally. If the insulation resistance drops to 0 ohms, the firing end is
fouled by either wet or dry carbon.
Overheating
When a spark plug overheats, deposits that have accumulated on the insulator
tip melt and give the insulator tip a glazed or glossy appearance.
Deposits
The accumulation of deposits on the firing end is influenced by oil leakage,
fuel quality and the engine's operating duration.
Lead Fouling
Lead fouling usually appears as yellowish brown deposits on the insulator
nose. This cannot be detected by a resistance tester at room temperature.
Lead compounds combine at different temperatures. Those formed at 370-470°C
(700-790°F) having the greatest influence on lead resistance.
Breakage
Breakage is usually caused by thermal expansion and thermal shock due to
sudden heating or cooling.
Abnormal Erosion
Abnormal electrode erosion is caused by the effects of corrosion, oxidation
and reaction with lead - all resulting in abnormal gap growth.
Melting
Melting is caused by overheating. Mostly, the electrode surface is rather
lustrous and uneven. The melting point of nickel alloy is 1,200~1,300°C
(2,200~2,400°F).
Erosion, Corrosion and Oxidation
The material of the electrodes has oxidized, and when the oxidation is heavy
it will be green on the surface. The surface of the electrodes is also pitted
and rough.
Lead Erosion
Lead erosion is caused by lead compounds in the gasoline which react chemically
with the material of the electrodes (nickel alloy) as high temperatures;
crystal of nickel alloy fall off because of the lead compounds permeating
and separating the grain boundary of the nickel alloy. Typical lead erosion
causes the surface of the ground electrode to become thinner, and the tip
of the electrode looks as if it has been chipped.
How Do I Repair My Car?
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How
Do I Change My Spark Plugs?
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