Neons.org FAQ on Stock Plugs
Neons.org FAQ on Spark Plugs and Wires
Neons.org FAQ on Oil in the Spark Plug Wells
Neons.org How To for Changing Spark Plugs
Champion RE14MCC5 (SRT-4)
NGK Part numbers:
Stock 7373FR5 (2.0 SOHC, DOHC)
Stock FR453686 (2.4)
Stock LZTR4A-11 (2.4 Turbo SRT-4)
Spark Plug Heat Range:
A spark plug's heat range has no relationship on the actual voltage transferred through the spark plug. Rather, the heat range is a measure of the spark plug's ability to remove heat from the combustion chamber.
The heat range measurement is determined by several factors:
*The length of the ceramic center insulator nose
*The insulator nose's ability to absorb and transfer combustion heat
*The material composition of the insulator
*The material composition of the center electrode
The longer the insulator nose gives you a larger surface area exposed to combustion gasses and heat is dissipated slowly. This also means the firing end heats up more quickly. We are talking about exposed ceramic length, not extended tip length.
Bearing in mind that the insulator nose length is a determining factor in the heat range of a spark plug, the longer the insulator nose, the less heat is absorbed, and the further the heat must travel into the cylinder head water journals. This means that the plug has a higher internal temperature, and is said to be a "Hot" plug. A hot spark plug maintains a higher internal operating temperature to burn off oil and carbon deposits, and has no relationship to spark quality or intensity.
Conversely, a "Cold" spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance, and allows the plug to operate at a lower internal temperature. A colder heat range can be necessary when an engine is modified for performance, subjected to heavy loads, or it is run at high RPMs for significant periods of time. The higher cylinder pressures developed by high compression, large camshafts, blowers and nitrous oxide, not to mention the RPM ranges we run our engines at while racing, make colder plugs mandatory to eliminate plug overheating and engine damage. The colder type plug removes heat more quickly, and will reduce the chance of pre-ignition/detonation and burnout of the firing end. (Engine temperatures can affect the spark plug's operating temperature, but not the spark plug's heat range).
Higher Compression Ratios and Forced Induction will elevate spark plug tip and in-cylinder temperatures.
Compression can be increased by performing any one of the following modifications:
a) reducing combustion chamber volume (i.e.: domed pistons,
smaller chamber heads, milling heads, etc.)
b) adding forced induction (Nitrous, Turbo charging, and Supercharging)
c) camshaft change
As compression increases, a colder heat range plug is required, as well as higher octane fuel and paying careful attention to ignition timing and air/fuel ratios are also necessary.
Thanks to Century Performance.
Grayish-tan to white in color indicates the plug is operating at the proper heat range as well as correct jetting and the cylinder is running healthy.
Electrode wear, misfire during acceleration and hard starting especially in damp or cold conditions.
Simply put as in its description, it's worn out ... it looks ok color wise, so replace it with same plug or at least compatible heat range. Change your plugs more often!
This is caused by foreign objects in the combustion chamber or an improper plug reach where it contacts the piston.
To solve this, make sure you have the correct length tip spark plug as well as removing any foreign materials in the combustion chamber.
In cases of severe detonation, insulators may become cracked or chipped. Improper spark plug gap settings will also cause the insulator tip to crack or chip.
Make sure that you are using the correct octane fuel first (Premium for DOHC / performance computers) and then verify correct ignition timing. Next check for an inoperative EGR system as well as proper function of the Knock Sensor. Also, you will want to make sure you are using the correct heat range plug, properly gapped.
Chalky appearance, white insulator, rapid electrode wear as well as an absence of deposits. The actual shell may also be discolored.
To cure this you must first verify that the plug is the correct heat range, the ignition timing settings are correct, the air/fuel mixture is not too lean, there are no vacuum leaks or sticking valves and that the EGR valve is functioning properly.
These are light-brownish deposits that are encrusted to the ground and/or center electrode. This situation is caused by oil and/or fuel additives. This condition can cause misfires.
The cure for this is to verify worn valve guides or valve seals, not using fuel additives, or you might even try changing fuel brands.
Oil Fouled (Wet)
Oily coating caused by poor oil control. Oil is leaking past worn valve guides, piston rings, or on some race engines a possible intake gasket leak and then entering the combustion chamber.
Check for worn valve guides, intake gasket sealing alignment, as well as worn cylinder walls and piston rings. A leak down test is a good place to start for what is causing this.
This will usually look as a melted center electrode and/or ground electrode.
Check for incorrect heat range plug, over-advanced timing, lean fuel mixtures, inoperative EGR valve or Knock Sensor (if equipped) and also look for hot spots or deposit accumulation inside the combustion chamber.
This will be pretty obvious ... melted and/or missing center and/or ground electrodes as well as a destroyed insulator.
Check for incorrect heat range plug, over-advanced timing, lean fuel mixtures, inoperative EGR valve or Knock Sensor and also look for hot spots or deposit accumulation inside the combustion chamber.) After you see this, you'd better look for possible internal engine damage as well. (pistons, cylinder walls, valves, rings, etc.)
Soft, black, sooty, dry-looking carbon. This indicates a rich mixture, weak ignition or wrong heat range plug (too cold.)
You will first need to verify plug heat range. Check for clogged injectors. Clean the air filter. Lastly on all engines, check for vacuum leaks and weak spark or low voltage output.
Thanks to Century Performance and Haynes Manual.