The spark plug is a small and inexpensive ignition system component. Still, it has a pretty tough job to do, considering the extreme engine compression pressures and combustion temperatures the spark plug is exposed to (inside its cylinder).
Sooner or later, one or several spark plugs will fail and cause engine performance problems. This article will answer some of the most commonly asked questions about the spark plugs on the 4.0L Ford Explorer, 4.0L Ford Aerostar, and 4.0L Mercury Mountaineer.
Contents of this tutorial at a glance:
- What Does A Spark Plug Do?
- Symptoms Of A Bad Spark Plug.
- What Causes A Spark Plug To Stop Working?
- How Do I Know My Spark Plugs Need Changing?
- Which Spark Plugs Should I Buy?
- Should I Use 100,000 Mile Spark Plugs?
- Important Tips And Suggestions.
- More Ford 4.0L Explorer, Aerostar, And Mercury Mountaineer Tutorials.
APPLIES TO: This tutorial applies to the following vehicles:
- 4.0L V6 Ford Aerostar: 1991, 1992, 1993, 1994, 1995, 1996, 1997.
- 4.0L V6 Ford Explorer: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
- 4.0L V6 Mercury Mountaineer: 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
What Does A Spark Plug Do?
The spark plug is the ignition system component responsible for igniting the air-fuel mixture within the cylinder.
It does this by having a spark jump from its center electrode to its side electrode.
Where does this spark come from? From the ignition coil pack. And it's delivered from the ignition coil pack to the spark plug by a spark plug wire (high tension wire).
Symptoms Of A Bad Spark Plug
Simply put, when a spark plug fails, it will not spark. Not to mention that the air-fuel mixture will not ignite.
When the air-fuel mixture does not ignite to combust, the cylinder will suffer a misfire.
Here's a basic list of the symptoms you'll see when a spark plug stops functioning:
- Rough idle.
- Bad gas mileage.
- Extended engine cranking (engine takes longer than usual to start).
- A heavier than normal exhaust smell coming out of the tailpipe.
- The engine is not as peppy as it used to be.
- Hesitation when you accelerate the vehicle on the road.
On the OBD II equipped vehicles, you'll see one or more of the following diagnostic trouble codes:
- Misfire trouble codes lighting up the check engine light:
- P0300: Random Cylinder Misfire.
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
- P0305: Cylinder #5 Misfire.
- P0306: Cylinder #6 Misfire.
What Causes A Spark Plug To Stop Working?
A few different factors can cause the spark plug to stop working.
The most common ones are:
- Normal wear and tear. In other words, they simply wear out.
- Carbon deposits block the air gap between the center and side electrodes.
- Damage caused by the installation process (for example, during a tune-up).
Engine oil burning inside the cylinder (the spark plug connects to) is the cause of the carbon deposits that block the air gap between the spark plug electrodes.
You can tell these engines apart because:
- They have blue smoke coming out of the tailpipe (when the engine is running or under load).
- They need to have engine oil added regularly.
How Do I Know My Spark Plugs Need Changing?
There's no fast rule that'll tell you that the spark plugs need to be changed.
For the most part, you'll need to replace the spark plugs if they meet one of the following three conditions:
- They've been removed and are showing signs of heavy wear and tear.
- They're causing an engine performance problem.
- You're following a recommended spark plug change interval.
Which Spark Plugs Should I Buy?
The Ford Motorcraft brand of spark plugs is the original equipment brand of spark plugs for your Ford Explorer (Aerostar, Mercury Mountaineer).
These are the spark plugs brand that I recommend you go with when replacing them.
Of course, any spark plug brand will work, as long as the spark plug is specifically designed for your particular Ford Explorer (Aerostar, Mercury Mountaineer).
Should I Use 100,000 Mile Spark Plugs?
Spark plugs advertised as having a service life up to 100,000 miles have platinum or iridium-tipped electrodes. Regular spark plugs, which have copper electrodes, do not last that long.
The catch here is that if the engine is in perfect working condition (e.g., it's not burning oil), these spark plugs will give you a service life of about 100,000 miles.
But if you've got a high mileage engine and it's burning oil, you won't see anywhere near 100,000 miles on those spark plugs. Carbon buildup will eventually close the air gap between the spark plug electrodes and cause a misfire.
Important Tips And Suggestions
The following tips will help you avoid some of the most common complications when replacing the spark plugs on your 4.0L Ford Explorer (Aerostar, Mercury Mountaineer).
TIP 1: Replace the spark plugs with a completely cold engine. Your vehicle's 4.0L engine has two aluminum cylinder heads which require removing the spark plugs with a completely cold engine.
Why? Because you run the risk of damaging the spark plug hole threads if you remove the spark plugs from a hot engine.
Trust me; this is a nightmare that you want to avoid!
TIP 2: Check the air gap of the new spark plugs with a spark plug gapper. Some spark plugs mentioned they're pre-gapped. I recommend that you check their air gap anyway.
NOTE: The exception to this is spark plugs like the Bosch Platinum+4 spark plugs. These spark plugs have multiple Ground electrodes, and they do not need to be gapped or checked at all.
TIP 3: Use a torque wrench to tighten the spark plugs. If you don't tighten the spark plugs enough, you risk having them come out as you're driving down the road. These loose spark plugs could also damage the spark plug hole threads in the cylinder heads.
If you over-tighten the spark plugs, you run the risk of damaging the threads of the spark plug hole.
The way to avoid any of these problems is to use a torque wrench to tighten the spark plugs. Now, it's easier said than done because some of the spark plugs are in very tight places, and it can be challenging to use a torque wrench on them. Still, you won't go wrong if you use a torque wrench.
More Ford 4.0L Explorer, Aerostar, And Mercury Mountaineer Tutorials
You can find a complete list of 4.0L Ford Explorer (Aerostar, Mercury Mountaineer) tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The Fuel Pump (Ford 4.0L Aerostar, Ranger, Explorer).
- How To Test Engine Compression (Ford 4.0L).
- How To Troubleshoot A No Start (Ford 4.0L).
- How To Test For A Blown Head Gasket (Ford 4.0L).
If this info saved the day, buy me a beer!
