Gasoline engines vary, but all of them have spark plugs that ignite fuel. Spark plugs need service from time to time.
A good plug carries battery current to the coil, which sparks combustion in the appropriate cylinder. If the plugs are going bad, the engine is going to run poorly. Under certain conditions, you may feel a rough idle and a lack of acceleration, and so on.
This article will provide a step-by-step guide for removing your spark plugs and inspecting their condition, as well as the tools needed to do it.
Now, you can compare the condition of your plugs to 9 different conditions to find out not only if your plugs are working, but you will be able to evaluate how well they are working, so you never have to rely on guesswork when troubleshooting issues.
Spark Plug Removal
Required Tools
Like any automobile service, having the right tools will make the job easier. For all spark plug removal and installation, I suggest the following basic hand tools and consumables:
- 3/8” drive ratchet
- 3/8” drive universal joint
- 3/8” drive extensions (3”, 6”, 10”)
- spark plug boot removal tool (only required for >20-year-old engines)
- Spark plug gap gauge
- 3/8” drive torque wrench (10-80 ft lbs)
- 3/8” drive spark plug socket (one of the below sizes):
- 13/16”/20mm (most full-size cars).
- 9/16”/14mm (Ford and newer Asian).
- 11/16″/18mm (old BMW).
- 14″mm bi-hex (new BMW).
- Tube of silicone dielectric grease.
- Shop manual for your vehicle.
In addition to the above, you may also need the following hand tools to safely access your spark plugs
- 3/8″ drive socket set
- Combination wrench set (3/8″ (10mm) to 1/2″ (13mm) sizes are included)
- Screwdriver set
- Channellock pliers (small)
- Shop vacuum with narrow crevice tool (best used to clean debris around spark plug holes)
Note: If you have a Ford with certain Triton engines, your spark plugs may remove themselves.
How to Remove Spark Plugs to Check Their Condition
Removing spark plugs is pretty straightforward, the challenge is accessing them.
This can often be an issue if your vehicle has a cross-mounted V6 engine. Generally, the plugs closest to the driver on V6 engines can be the most difficult to reach.
- Open the hood. Cover each fender with an old, but clean bath towel to avoid scratching the paint if your belt buckle is in the way. Check out the engine arrangement and see the best way to access the plugs. Remove any insulator cover(s), panels, or covers that inhibit access to the plugs.
- You’ll have to remove (or move aside) anything in the way, like wiring harnesses, hoses, and electrical modules, to access the area over each plug.
- In most modern vehicles, each spark plug will have its own coil pack module (the spark coil) above each of the plugs. For older vehicles, a single, large-diameter wire will go to the top of each spark plug, so there won’t be a coil above it.
Tip: It can be handy to mark the location of each plug and the connector of the spark plug wire or coil harness so you can re-attach everything in the correct position during the reassembly.
Sometimes, coils only fit in one exact way. Look at how the coils are currently positioned so you can install them correctly. It may help to take a picture or two with your mobile phone to help get the pieces installed correctly later.
- If there is a spark coil above each spark plug, then the coils will have to be removed. Each coil will have a low-voltage cable that is connected to a connector; the cable must be disconnected.
- You will want to take note of this connector. It will likely have some type of snap latch that will have to be moved or pressed to release the connector. Often, you can identify the latch because they are often a different color from the connector. Use a screwdriver to release the latch; you should be able to pull the connector off the coil housing.
- Next, you will need to remove the fastener that is holding the coil securely in place and pull the coil out of the spark plug.
Tip: It is a good practice to have a plastic bin or bucket to toss the separated parts into, and keep them all in one area. This will make finding any parts to reinstall them easier later.
- If there is no spark coil on top of each plug, you will want to use the boot removal tool to pull the spark plug boot straight off the plug; always try to grab the boot as close to its base as possible. Wiggling the boot gently while pulling will also help get it free. Never pull the boot off by grabbing the spark plug wire, too.
- Take off the spark plug with the correctly sized socket, extension, and universal joint if needed. Make sure to identify or tag each spark plug, so you will know which cylinder they came from each plug came from. If the spark plug hole is accessible, wipe the flat or tapered seat in the cylinder head with a clean cloth. With your Shopvac (or your household vacuum), use the crevice nozzle to suck dirt away from this area.
Note: Be careful when working on a spark plug; it is easy to drop a small part (or dirt) down into the spark plug hole. Even dropping a small screw down into the combustion chamber could cause major engine damage.
Spark Plug Conditions and Colors
Each spark plug takes its colors and conditions from whatever is going on in the combustion chamber. So, hopefully, some inspection of the spark plugs in your engine will tell you the story.
You may find it useful to know which cylinder each spark plug came from because, later on, you may have to tell your service technician which cylinder has the problem.
1. Normal Condition.
The insulator that surrounds the center electrode is grayish-white, or grayish-yellow to brown. The side electrode is clean. This means your combustion processes are normal.
There may be some very light oil burn, but nothing to worry about. Your engine is operating normally.
2. Sooted/Carbon Fouled.
The surfaces of the spark plugs are uniformly coated with dull black deposits.
Cause: Engine is running rich (too much fuel); dirty air filter; engine startup fuel-air mixture control not operating properly; driving short distances; use of the wrong spark plug.
3. Oil Fouled.
Parts of the plugs are wet or have a shiny black coating.
Cause: Excess oil in the combustion chamber due to: oil level too high; crankcase venting system not operating properly; worn-out piston rings and/or valve stem seals.
4. Lead Fouling.
Parts of the plugs are coated with brownish-yellow glazes, which can include a greenish tinge. The glaze can be thin (or thick and/or partially chipped off).
Cause: Use of leaded fuel (not present in the USA) or use of fuel additives containing lead.
5. Ash Fouling.
The parts of the plugs are coated with a light-colored, thick, ceramic-like compound that is brittle. It may be stripped off with a fingernail or a jackknife.
Cause: Excessive use of fuel and/or oil additives.
6. Center or Side Electrode Eroded/Melted Away.
The center insulator may also be blistered or soft.
Cause: Overheating of plug and combustion chamber due to poor quality fuel (octane rating too low); ignition timing over advanced; pre-ignition; engine running lean; use of wrong spark plug.
7. Heavy Wear of Center Electrode.
The center electrode of the spark plug is partially or completely gone.
Cause: Spark plug has outlived its service life; the plug gap is too big; use of the wrong spark plug.
8. Heavy Wear on Side Electrode.
The side electrode of the spark plug is partially or completely gone.
Cause: Poor quality fuel (octane rating too low); pre-ignition; excessive use of fuel and/or oil additives.
9. Center Electrode Insulator Nose Fractured.
The spark plug has a small piece of insulator missing.
Cause: Mechanical damage (plug was dropped); excessive deposits around center electrode; spark plug has exceeded its service life.
Notes:
- Old spark plugs can’t be properly cleaned. Any of the plug conditions noted above in 2 through 9 will, at a minimum, require the installation of new plugs.
- The plug conditions observed in 2, 3, 6, and 8 should spur further investigation of the engine, fuel, and ignition systems by a qualified service technician for corrective measures.
Installing New Spark Plugs
- Remove the bags from your new spark plugs. For the manufacturer-specified gap and gap tolerances, it is also recommended to check them before installation. You can find gap dimensions in your service manual and/or parts information.
- Using a gap tool, measure the distance between the center electrode and the side electrode. Gap tools for spark plugs can set both a distance gap between the electrodes, or you can measure with the bendable tab method. The gap for factory spark plugs with multiple side electrodes (two or more) is usually pre-gapped and has additional side electrode features.
- There should be no more than one slight bend of the electrode. Use the bending tab on the gap tool to slightly bend the side electrode into position and to establish the correct gap. Be careful not to over-bend. Measure and set the gap for each plug.
- Securely place a new plug into the spark plug socket. You can help guide the socket and plug down into its threaded spark plug hole on your engine. It may be easier if you use an extension on the socket, or if the socket has a retention grip, to hold the plug in place.
- Now manually turn the socket CW (clockwise) to thread the plug into the hole and screw it in. The plug should easily screw into its place. If the plug does not screw into its location easily, you may be cross-threading the plug. If so, do not force it further in; rather, remove it, realign it by hand, and try to hand-tighten it in again. Once you have it hand tightened into the threaded hole of the engine, manually screw it entirely.
- Determine the spark plug tightening torque in your service manual. If your torque wrench is adjustable or has a torque dial, set it to the value in the service manual. Using your torque wrench, tighten the plug with the appropriate torque setting.
- Very lightly coat the inside diameter of the plug boot with dielectric grease. Firmly push the makes or connectors of the plug wire or coils onto each spark plug. Reattach the power connector to each spark coil back into its factory position.
- Repeat Steps 2 through 4 for all the plugs.
- Reinstall any components taken off to access the plugs. Return the harnesses, hoses, and/or any modules that were moved aside during the access for installation. Further, check if any wiring or hoses could potentially be in contact with exhaust heat before finishing installing other components.
- The plugs have been installed, proceed to start the engine and confirm it starts and sounds normal.
Why Modern Spark Plugs Last Longer?
As stated above, spark plugs are designed to ignite the fuel-air mixture in each engine cylinder.
When spark plugs can perform their intended action, they last a long time. Just not long ago, spark plugs generally had to be changed every 10,000 to 12,000 miles.
However, spark plugs today can exceed 100,000 miles, and you may not even have to service them before they hit that mileage! What has changed?
#1. Fuel Injection.
Number one, automobiles and trucks today are fuel-injected and computer-controlled fuel-air mixtures due to the exhaust-prone Engine Control Module (ECM).
The leading cause of the deterioration of spark plugs is excessive heat! A controlled fuel-air mixture creates more uniform combustion at lower temperatures than engines of last year.
#2. Unleaded Gas.
Number two, we don’t see lead in domestic gas anymore, which has also contributed to longer plug life.
When leaded fuels were used, lead buildup on the spark plug electrodes created corrosion on the plugs, thus inhibiting proper spark activity and operation.
#3. More Durable Materials.
Number three, spark plugs we find today are made of far more durable materials than those of earlier years. Today, spark plugs are the least guilty in the exhaust environment because the electrical current-carrying component (namely the center electrode) is typically made of expensive platinum, iridium, or copper.
These materials make sure the plug anode does not burn away quickly and create an overall more efficient electrical current-carrying process than older plug designs.
Common spark plugs using these modern materials and their benefits are discussed here.
It is highly advised to use the best quality spark plugs if you want to maximize the life and performance of your engine, which also includes trying to achieve the manufacturer’s recommended miles for spark plug replacement.