The spark plugs may be some of the smallest parts on your engine, but they have one of the toughest jobs. Every time the engine is running, each spark plug has to ignite the air/fuel mixture in its cylinder thousands of times every minute.
After years of service —and often hundreds of thousands of miles— it's not unusual for spark plugs to become worn, carbon fouled, or even coated with engine oil as the engine ages.
In this tutorial, I'll explain the most common ways spark plugs fail, how to recognize the signs they're due for replacement, and which spark plugs are the better choice if your 2.2L Buick Century is starting to burn a little oil.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 2.2L Buick Century: 1993, 1994, 1995, 1996.
Why Spark Plugs Fail On High-Mileage Engines
No spark plug lasts forever. Every time a spark jumps across the gap between the center electrode and the Ground electrode, a tiny amount of metal is eroded away. It happens a little at a time, but after enough miles, that wear increases the gap and makes it harder for the spark plug to ignite the air/fuel mixture efficiently.
How long a spark plug will last depends largely on the type installed. As a general rule, you can expect something like this:
- Copper spark plugs: Typically provide about 50,000 to 60,000 miles of dependable service.
- Platinum spark plugs: Under normal operating conditions, they can often last close to 100,000 miles.
Those service-life estimates assume your 2.2L engine is in good mechanical condition and isn't consuming engine oil.
On a high-mileage 2.2L engine, that isn't always the case. If the engine is burning oil, the spark plugs can become oil and carbon fouled long before they wear out. As the oil burns inside the cylinders, it leaves deposits on the spark plug electrodes. Over time, those deposits interfere with the spark and can cause the affected cylinder to misfire.
When this happens, you'll usually notice a rough idle, sluggish acceleration, and bad gas mileage.
If your Buick Century is a 1996 model (OBD II-equipped), the PCM will usually detect the misfire, illuminate the check engine light, and store a cylinder-specific misfire trouble code. Depending on which cylinder is affected, you'll usually see a P0301, P0302, P0303, or P0304 diagnostic trouble code.
When Should I Replace The Spark Plugs?
Knowing when it's time to replace the spark plugs on your 1993-1996 2.2L Buick Century comes down to one simple question:
Is the engine burning oil, or isn't it?
If your 2.2L engine isn't using any noticeable amount of oil, spark plug replacement is pretty straightforward. Just replace them at the interval recommended in the owner's manual or service manual.
If the engine is burning oil, it's a different story. As the oil burns in the combustion chambers, it leaves carbon deposits on the spark plug electrodes. Eventually, those deposits weaken the spark and can cause a rough idle or cylinder misfire well before the spark plugs reach their normal service life.
If your 2.2L Buick Century is using oil, these are the most common signs that it's time for a fresh set of spark plugs:
- The engine develops a rough idle or begins to misfire.
- On 1996 models (OBD II-equipped), the check engine light comes on and a cylinder-specific misfire trouble code is stored.
Not sure whether your engine is burning oil? Here are a few telltale signs:
- You have to add engine oil between scheduled oil changes.
- You notice blue smoke coming from the tailpipe while accelerating.
- You see blue smoke from the exhaust when you first start the engine, especially after it's been sitting overnight.
If your 2.2L engine isn't burning oil, you can usually expect the spark plugs to last their full service life. As a general guideline:
- Copper spark plugs (OEM type): Replace them about every 50,000 to 60,000 miles.
- Platinum spark plugs: They can often last up to about 100,000 miles under normal driving conditions.
Which Spark Plugs Should I Buy: AC Delco Or Brand X?
Your 1993-1996 2.2L Buick Century originally came from the factory with ACDelco copper spark plugs. They're still an excellent replacement choice today, but they're by no means the only good option.
Spark plugs from trusted brands like NGK, Autolite, Bosch, and other well-known manufacturers will also perform well. In reality, choosing the right spark plug has less to do with the brand name and more to do with the condition of your engine.
If your 2.2L engine is burning oil, sooner or later the spark plugs are going to become carbon and oil fouled regardless of whose name is on the box. In that situation, spending extra money on platinum or iridium spark plugs usually isn't worth it because they'll eventually foul just like copper plugs.
If your engine isn't using oil, it's a different story. Premium spark plugs can be a worthwhile upgrade since they'll generally provide a much longer service life than conventional copper spark plugs.
Here's the approach I recommend:
- The engine is burning oil: Install a quality set of copper spark plugs and save your money. Since oil fouling will eventually shorten the life of any spark plug, there's usually no benefit to paying extra for platinum or iridium plugs.
- The engine isn't burning oil: You can stay with OEM-style copper spark plugs or step up to platinum spark plugs if you want the longer replacement interval. Either option is a good choice.
Other Things That Can Kill A Spark Plug
Normal spark plug wear and carbon fouling aren't the only reasons a spark plug stops firing. Quite often, the spark plug isn't the real problem at all. Instead, another ignition or engine issue is preventing it from doing its job.
When that happens, the result is usually the same: the affected cylinder begins to misfire, the engine runs rough, and on 1996 models, the check engine light may turn on.
Here are some of the most common causes:
- Leaking fuel injector: A fuel injector that's leaking or stuck open can flood the cylinder with fuel and foul the spark plug.
- Faulty spark plug wire: A damaged, worn, or high-resistance spark plug wire can keep the spark from reaching the spark plug.
- Failed ignition coil: A failed ignition coil can prevent one or more cylinders from getting a strong spark.
- Low engine compression: Low engine compression can lead to incomplete combustion, eventually causing the spark plug to foul.
- Engine burning oil: An engine that's burning oil can quickly coat the spark plug with carbon deposits, leading to a cylinder misfire.
It's also possible to ruin a brand-new spark plug during installation. Here are some of the most common mistakes:
- Over-tightened spark plug: Over-tightening the spark plug can crack the porcelain insulator and damage the spark plug.
- Dropped spark plug: Dropping the spark plug before installation can crack or weaken the porcelain insulator, even if the damage isn't immediately visible.
- Incorrect spark plug gap: Accidentally changing or closing the spark plug gap while handling it can affect spark performance.
- Gap not verified: Always verify that the spark plug gap matches the specification for your 2.2L engine before installing the spark plug.
- Thermal shock: Spraying water on a hot engine can rapidly cool the porcelain insulator and cause it to crack.
REAL-WORLD CASE STUDIES:
Having spent what seems like a lifetime diagnosing and wrenching on cars, I've run into plenty of misfire issues caused by simple installation mistakes —and, of course, quite a few caused by low compression and spark plugs covered in carbon tracks. I've written down some of those experiences, and you can read those real-life case studies here:
- Diagnosing A Toyota Corolla Misfire Case Study —a misfire caused by a simple installation error.
- Troubleshooting A Hard To Diagnose Misfire Case Study (GM 3.1L, 3.4L) —this one involved low compression causing a stubborn cylinder misfire (it was my brother-in-law's car, too).
- Carbon Tracks Are A Common Cause Of Ignition Misfires —spark plug and spark plug wire boot with carbon tracks causing a cylinder misfire (at: easyautodiagnostics.com).
More 2.2L Buick Century Diagnostic Tutorials
You can find a complete list of diagnostics tutorials and wiring diagrams for your 2.2L Buick Century in this index:
Here's a small sample of the tutorials you'll find:
- How To Test For A Blown Head Gasket (1993-1996 2.2L Buick Century).
- How To Test Engine Compression (1993-1996 2.2L Buick Century).
- How To Test The TPS With A Multimeter (1993-1996 2.2L Buick Century).
- How To Test The MAP Sensor (1993-1996 2.2L Buick Century).
If this info saved the day, buy me a beer!
