By A-Train




There has been a lot of talk on the subject of spark plugs and there is a lot of confusion and misinformation. I wrote this report up to help you pick the right spark plug for your application and understand why. This report may or may not affect your application.


Lets start with a spark plug. As you know, a spark plug is the device that is used in an internal combustion engine to ignite the air fuel mixture in the combustion chambers. A spark plug is threaded into the cylinder head and protrudes into the cylinder area. It normally has two electrodes which project into the combustion chamber (cc). When the spark ignites the air/fuel mixture, the energy expands and forces the piston downward. The ignition system (which I won’t get into at this point) on the 4.6L is either a DIS or E-DIS system (electronic distributor less ignition incorporated into the later EEC-V computers). High voltage is passed from an energized coil pack, through spark plug wires and to the spark plugs. There are a few exceptions to this.




1991-1997 4.6L Crown Vic/Grand Marquis uses spark plug wires

1994-1997 4.6L T-Bird/Cougar uses spark plug wires

1996-1998 4.6L Mustang GT uses spark plug wires

1993-1997 4.6L 32V Mark VIII uses spark plug wires

Of course there are the Town Car and the modular trucks as well.


Ford eventually went with the coil-on-plug ignition system for their newer cars. The first production Ford to receive the coil-on-plug system was the 1996 Taurus SHO. The following vehicles received coil-on-plug as well.


1998-present 4.6L Crown Victoria/Grand Marquis

1999-present 4.6L Mustang GT

1999, 2001, 2003 4.6L 32V Mustang Cobra (’03-‘04 supercharged)

1999-present Lightning 5.4L supercharged

1998 4.6L 32V Mark VIII


There are others on the list, but I feel that covers our topic range. So moving on, regardless if the system has spark plug wires or not, it still has coils and spark plugs. The energy released by the coil is sent through the spark plug to the electrodes. The current then arcs or jumps the gap between the center electrode and the ground electrode. This ignites the fuel vapor in the combustion chamber. It is possible for the coil to release up to 40,000 volts or more. The higher the voltage, the hotter the spark. The hotter the spark, the better burning it will be and the more power you will make.


There are many different types of spark plugs. From retracted gap/tip, regular gap/tip, cut back ground (used in some NASCAR applications), fine wire electrode, medium wire electrode, projected nose, and surface gap. I’m sure I left a few out. Now we are going to talk Motorcraft spark plugs and applications.


Stock 4.6L Non-PI and PI engines normally use an AWSF-32 plug in either Copper or Platinum*. This is a nominal range for all purposes. The AWSF prefix letters tell what type of spark plug it is, or its family. Normally the prefix tells the thread length, the type of taper, the suppressor type, etc. If you are interested in the exact meaning of each prefix, pick up a Ford Motorcraft spark plug specification book. Moving on, the number is always the heat range. AWSF-62C would be a hot plug. AWSF-2C would be a cold plug. I will get into heat ranges later on. The suffix in the part number is the type of material the center electrode is made of and/or the ground electrode. AWSF-32C is copper. AWSF-32PP is platinum (platinum ground and electrode). Most early 4.6L engines used copper spark plugs which are fairly standard. First, copper is readily available and cheaper than other materials.




Let me explain the DIS ignition system now. The Ford DIS/E-DIS system works on a waste spark management. One half of the spark plugs fire from the center electrode to the ground electrode and the other half fires from the ground electrode to the center electrode. The EEC fires two spark plugs simultaneously. One spark plug on the compression stroke uses the majority of the coils stored energy, the other spark plug on the exhaust stroke uses very little of the coils stored energy. This is the reason why you may have found AWSF-32PG and AWSF-32P plugs in your 1996 and later 4.6L vehicles when changing spark plugs. Only half of the plugs will wear out faster than the others. Ford only needed half of the spark plugs to be full platinum, so this was done to save cost. The replacement for these are AWSF-32PP, or 8 double platinum plugs. Later on Ford changed their suffix designation on the platinum plugs to “EE”.


The ignition coils contain two separate ignition coils. Each coil is controlled by the ignition control module through two coil leads. Each ignition coil activates two spark plugs simultaneously:







Materials used for spark plugs can dramatically alter longevity, efficiency, power, and even knock sensitivity. We will discuss three types of materials used today to manufacture spark plugs. The first is Copper, which is becoming more and more expensive.  Copper melts at 1,981 degrees F and that makes it suitable for an internal combustion engine. It’s a great conductor of electricity (second to silver), heat and can resist corrosion to a point. Copper is very soft and can be easily drawn into wires. The majority of the spark plugs on the market today are copper since it is the most economical of the material to use. Nickel is also used as an alloying material for a copper spark plug. However car makers have be using platinum plugs in their engines to increase the tune-up intervals.


Platinum is a precious metal and it is rare, that makes it more expensive than copper. It melts at 3,200 degrees F. and it is highly resistant against corrosion. Platinum has a high fuse point with high electrical resistance. It is also harder than copper, making it very useful for longevity of a spark plug. Make no mistake, copper is a better conductor than platinum.


Finally, we will discuss Iridium. Iridium, is extremely hard and brittle material and extremely rare as well. The melting point is 7,466 degrees F. and it is considered the densest of elements. Iridium is used solely as an alloying material for platinum. Platinum alloys contains a small amount of iridium which is much harder than pure platinum.






Heat ranges of a spark plug are often misunderstood and neglected. The term heat range refers to the relative temperature of the core nose of the spark plug. “Hot” and “cold” terms refer to the thermal characteristics of the spark plug or the ability for the spark plug to remove heat from its firing tip and combustion chamber. A cold spark plug transfers heat faster from its firing tip into the insulator. This is due to the shorter insulator nose it has. That helps keep the tip of the plug from glowing red and accidentally pre-igniting the air/fuel mixture. The heat is transferred into the cylinder head and engine coolant. A cold plug is used on high compression engines or extremely high cylinder pressure situations (i.e. superchargers, nitrous, or turbochargers). A hot spark plug transfers heat from its firing tip, slowly. The hot spark plug is used in a low compression engine to avoid fouling since the combustion chamber temperatures are low.


It is important to remember that a spark plug does not create heat; it simply removes it acting as a heat exchanger. The way the spark plug companies control heat ranges is to normally vary the length of the core nose or the alloy of the material used in the electrodes. So a hotter plug will have a longer insulator nose and therefore a long heat transfer path. Cold spark plugs have a short insulator nose and can transfer heat much faster. A cold plug reduces the chances of knock, making the engine less knock constrained.


The trade off is fouling. A colder spark plug is prone to fouling faster than a hotter one. Let me explain why. A spark plug must reach a certain temperature for it to burn off any carbon in the combustion chambers. Also the same applies to fuel. If the plug is to cold, it may not reach its cleaning temperature during normal driving and that will cause the plug to accumulate deposits. If the deposits aren’t burned off, the chance for a misfire or when the air/fuel mixture is not ignited properly or at all can occur. Since a hot plug retains more heat before transferring it to the engines cooling system, it can burn off these deposits more efficiently. Likewise, if a spark plug is subjected to extreme temperatures that exceed 1,000 degrees C., the spark plug can blister and sometimes melt. Just so we are clear, the heat range of the spark plug has no effect over voltage or resistance required to jump the gap.  The hotter the spark plug (heat range), the more efficient it will be and the hotter the burn will be.



The rule of thumb is if you beat on the car and go to WOT (wide open throttle) often, you can get by with one heat range lower. Motorcraft offers an AWSF-22C plug for this. You effectively dropped one heat range colder than stock. If you have no modifications that warrant a colder plug, you will not benefit from them. In fact it may hurt performance. If you run a supercharger or nitrous oxide, you want to go as low as you can with the heat range without fouling up. The ’99-present 5.4L supercharged Lightnings use a spark plug two heat ranges colder than stock. The ’99-’00 Lightning used a medium platinum wire electrode plug with full threads. The part number is AGSF-12EE. I believe the AGSF-12EE plugs have been superceded with the newer plugs that I’ll talk about next. The ’01 to present Lightnings used a newly designed sparkplug with a fine wire platinum/iridium electrode. The part number is AGSF-12FM1. Again it is two heat ranges colder than stock in the AGSF family.


If you are running more spark advance via a custom tune or chip and you have a few more advanced modifications, drop two heat ranges colder than stock. If you are running a supercharger or nitrous go with AGSF-12FM1 plugs or AWSFA-12C plugs. The AWSFA-12C plugs are in the AWSF family. They are two heat ranges colder than stock, medium wire electrode and copper. These are excellent for performance and very reasonable price wise, even when you are changing plugs often (which you should do).


Now, the 32V Mark VIII (DOHC) engines have knock sensors from the factory. The EEC essentially listens to the engine for harmful knock. Since the onset of knock is lower than a human can ear, the sensor tells the EEC to pull timing out before you even know anything is happening. So as a very wise man once told us, these engines are already knock constrained from the factory and are pulling timing even with premium gasolines with higher octane ratings. So switching to an AGSF-12FM1 or an AWSFA-12C plug reduces the chances of knock, therefore the EEC doesn’t get a chance to pull spark out. The result is you gain back lost power and a good amount of it. The plug itself is not responsible for more power, the spark advance is. Most of the 4.6L SOHC 2V engines do not have knock sensors so this doesn’t apply.






The term gap means the area between the center electrode and the ground electrode on a regular type of spark plug. The gap setting on spark plug is critical in efficiency and power production as well as emissions. All things being equal, the larger the gap, the more power you can make. Provided the spark can jump the gap between the electrodes. If this does not occur, you have a misfire or a dropped cylinder. On the 4.6L 2V engine, the gap should be set at 0.054” with a stock ignition. That means the space between the electrodes should be fifty four thousands of an inch. Always set the gap on a new spark plug when you take it out of the box. They are normally not set to your vehicles specifications and if not properly set, you will suffer in the performance department. To determine your specific gap requirements and plug types, either check the VECI sticker under your hood or consult with a Ford Motor Company or Helm service manual. Use a feeler gage or gap tool to adjust the gap.


Now on a supercharged, nitrous oxide injected or turbocharged engine, your cylinder pressures are much higher than a naturally aspirated engine. As cylinder pressure increases, the energy needed to jump the gap between electrodes does too. Unfortunately, the stock ignition isn’t powerful enough to provide the additional spark voltage required to jump the gap. Effectively, you are blowing the spark out under boost or when the nitrous is applied. Most people simply reduce the gap on the spark plug when boost is a factor in the equation. This means the distance the spark has to jump is reduced and the resistance has dropped. On the 4.6L engine with 6-10 psi of boost, you can get away with a gap between 0.035-0.040”. More than 10 psi of boost is pushing the limits of the stock ignition and you really need to upgrade to a more powerful voltage supply. MSD and a few other companies make hotter ignition systems. The lower the gap setting, the less power you will make though. Ideally, with a blower, you want to run as close to the stock gap as possible. This cannot always be done and with the stock 4.6L ignitions it’s down right impossible. There is another solution though.


Denso makes an iridium type sparkplug with a tiny “u” groove channel in the ground electrode. Some of you smarter types may have noticed the similarities between the Lightning FM1 plug and the Denso iridium plugs. The iridium makes the tip of the electrode very hard. The manufacturers are able to reduce the overall diameter of the center electrode, making the tip, very thin and to a point. This dramatically reduces the voltage required to jump the gap. As we all know, electricity flows to the path of least resistance. So with a larger gap and a supercharged engine, you picked up power. The power did not come from the spark plug itself, but rather from the larger gap area that provided a larger flame kernel. The material and electrode size allowed the plug to be gapped at the stock specifications under extreme cylinder pressure situations.


A wise man has told us over and over again, use the Lightning plugs on any supercharged 4.6L or 5.4L engine. Now you understand why. Not only are they able to transfer heat faster than a stock spark plug, the newer FM1 plugs can reduce the resistance and reduce the chances of misfires on a supercharged or nitrous application.







Updated to include some corrections


*Stock 4.6L 2V spark plugs for NON-PI headed and PI headed vehicles:



Copper type plugs – Medium wire electrode – HALF thread type – stock heat range


Double Platinum type plugs – Medium electrode – HALF thread type – stock heat range


*Note: Some early model 4.6L 2V engines require a FULL threaded spark plug design. It has been brought to my attention that a 1992 4.6L (gasoline) Crown Victoria engine used AGSF-32C plugs.


CAUTION: If your engine requires an AGSF type spark plug (full thread) and you attempt to install an AWSF type plug (half thread) you will be inserting the unthreaded portion of the spark plug into the threads of the cylinder head prior to the taper seat of the spark plug and the cylinder head comes in contact with it. This would tear up the threads and require a heli-coil to repair them or replacement of the cylinder heads. 


The only 4.6L Modular heads I know of that require full thread plugs are the SVO (Ford Racing Performance) heads.  An AGSF (full thread) spark plug will work in any Modular cylinder head, you'll just be using only the bottom portion of the threads on the plug in a half threaded cylinder head. However, an AWSF (half thread) plug will NOT work in a cylinder head REQUIRING a full threaded plug.



*One heat range colder than stock for NON-PI headed and PI headed vehicles:



Copper type plugs - Medium wire electrode – HALF thread type – one heat range colder than stock.


*Two heat ranges colder than stock for NON-PI headed and PI headed vehicles:



Copper type plugs – Medium wire electrode – HALF thread type – two heat ranges colder than stock.


Double platinum type plugs – Medium wire electrode – FULL thread type – two heat ranges colder than stock.


Iridium/platinum type plugs – FINE wire electrode – FULL thread type – two heat ranges colder than stock.




Stock heat range:




Two heat ranges colder than stock:




CAUTION: DO NOT attempt to install AWSF type spark plugs into SVO/FRPP cylinder heads or damage to the threads can occur.


Also, these plugs are not to be used as a band aid for running lower than required octane rated gasoline’s in your engines. That’s working against yourself. Go as low as you can with the octane rating before it pings then move up a step (RON number). You will make the most power there. Remember, the higher the octane (RON), the less volatile the fuel and the more likely it will resist the initial burn. The lower the octane number the more volatile the fuel and more likely it is to explode when mixed with air and spark is present. Running 100 octane gasoline in your stock ’96 Crown Victoria is a waste of money. If you are running a chip or other means to advance the spark timing, then you may need to run 93 or higher octane. Combine that with the colder plugs and a lower temperature thermostat, you have dramatically reduced the engine from being knock constrained.



Furthermore, the colder plugs DO NOT offer a power increase by themselves nor do increase/decrease the voltage requirement, durability or performance, they can help you make more power.


So the bottom line is, use one heat range colder than stock if you abuse the car or see WOT often. If you have a chip that adds timing, drop two heat ranges. This is up to you, but we all agree it’s a better solution to use two heat ranges colder than stock. If you are supercharged or run nitrous oxide, this is a no-brainer, go with Lightning plugs or AWSFA-12C. Some of you have a few modifications and a chip. You also do not go to WOT often and most of your driving is stop and go, if this applies to you, then you do not want a plug that is two heat ranges colder than stock. They will foul up and cause you drivability concerns.