What Do The Spark Plugs Do? (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma)

The spark plugs in your 2.5L Chevrolet S10 pickup or GMC S15 pickup have one of the toughest jobs to do in your engine, as they're subjected to an enormous amount of heat and pressure from the cylinder to which they are connected.

Under that heat and pressure, they must deliver a spark to ignite the air-fuel mixture swirling in the cylinder. This process continues as long as the engine is running.

While the spark plug is probably the smallest of all of the components that make up the ignition system, it plays an outsized role in keeping your Chevy S10 pickup or GMC S15 pickup's 2.5L engine running at its best.

In this article, I'll answer some of the most commonly asked questions about spark plugs.

You can find this tutorial in Spanish here: La Bujía ¿Qué Es Y Para Que Sirve? (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.5L Chevrolet S10 Pickup: 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993.
• 2.5L GMC S15 Pickup: 1985, 1986, 1987, 1988, 1989, 1990.
• 2.5L GMC Sonoma: 1991, 1992, 1993.

What Does A Spark Plug Do?

The role of the spark plug is to provide a spark that ignites the air-fuel mixture in the cylinder to which it is attached.

This spark is generated when the spark plug receives a high voltage spike from the ignition coil.

The high voltage must now jump the gap between the spark plug's center and side electrodes. The physical manifestation of the high voltage flowing between these two electrodes is a spark.

Symptoms Of A Bad Spark Plug

The spark plugs are a critical ignition system component that play an important role in starting and keeping the engine running optimally.

Although it doesn't happen overnight, sooner or later one or more will fail. When a spark plug failure occurs, you'll see one or more of the following symptoms:

• Cylinder misfire.
• 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.
• Fuel smell coming from the tailpipe.

What Causes A Spark Plug To Stop Working?

The most common cause of spark plug failure is normal wear and tear. Specifically, the spark plug's electrodes wear out and can no longer generate spark.

Another common cause of spark plug failure, especially in high-mileage engines, is carbon deposits blocking the air gap between the center and side electrodes of the spark plug.

Carbon deposits blocking the spark plug's electrodes are usually caused by engine oil burning in the cylinder the spark plug is connected to.

You can distinguish these engines because:

• Blue smoke comes from the engine's exhaust pipe (with the engine running or under load)..
• The engine must be regularly topped up with engine oil.

Last but not least, spark plug failure can be caused by damage during installation (e.g. during a tune-up).

How Do I Know My Spark Plugs Need Changing?

It's time to replace the spark plugs when one of the following conditions has been met:

• The spark plugs are showing heavy wear and tear.
• The spark plugs are causing an engine performance problem.
• You're following a recommended spark plug change interval.

Which Spark Plugs Should I Buy?

AC Delco spark plugs were installed in your Chevy S10 pickup or GMC S15 when it was being built at the factory.

I've always been a firm believer in using the same brand of spark plugs the vehicle came with from the factory.

So when it comes time to replace the spark plugs in your vehicle, I recommend you buy and install the AC Delco brand of spark plugs.

Having said that, any other brand of spark plug specifically designed for your vehicle will work.

Should I Use 100,000 Mile Spark Plugs?

Spark plugs advertised with a service life of up to 100,000 miles have platinum or iridium tipped electrodes. Normal spark plugs with copper electrodes don't last that long.

Now the problem here is that if the engine is in perfect working condition (e.g. it doesn't burn oil), these spark plugs will give you a service life of around 100,000 miles.

But if you have a high-mileage engine that burns oil, you won't see anywhere near 100,000 miles on those spark plugs.

Carbon buildup will eventually close the gap between the spark plug electrodes and cause a misfire.

Important Tips And Suggestions

Here are a couple of important tips that will save you time (and frustration) when replacing spark plugs:

TIP 1: Replace the spark plugs with a completely cold engine. The cylinder heads of your 4.3L V6 engine are made of aluminum, and this means that the spark plug hole threads can easily be stripped if the spark plugs are removed with a hot engine.

Stripping the spark plug hole threads in the cylinder head is a nightmare that can easily be avoided by removing the spark plugs with a completely cold engine.

TIP 2: Check the air gap of the new spark plugs with a spark plug gapper. Don't trust that the spark plugs are already pre-gapped.

I've diagnosed quite a few misfire problems that were caused by spark plugs that were advertised as being pre-gapped but were not.

TIP 3: Use a torque wrench to tighten the spark plugs. If you don't tighten the spark plugs enough you run the risk of having them come out as you're driving down the road. This could also damage the spark plug hole threads in the cylinder heads.

If you over tighten the spark plugs, then 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.