Common Causes Of Spark Plug Failure (1991-1995 1.9L Ford Escort, Mercury Tracer)

  • By: Abraham Torres-Arredondo
  • Created: 11 September 2025
  • Updated: 11 September 2025
  • Articl Id: 8
Common Causes Of Spark Plug Failure (1991, 1992, 1993, 1994, 1995 1.9L Ford Escort, Mercury Tracer)

Spark plugs may be small ignition components, but they play a critical role in keeping your Ford Escort or Mercury Tracer running smooth every time you start the engine.

When one or more spark plugs begin to wear or fail, engine performance issues will show up right away: cylinder misfires, rough idle, and a noticeable drop in performance.

When one or more spark plugs wear out or fail, you'll notice problems right away: misfires, rough idle, and loss of performance.

In this guide, I'll walk you through the common reasons spark plugs fail and how you can tell it's time to swap them out.

Contents of this tutorial:

APPLIES TO: This tutorial applies to the following vehicles:

  • 1.9L SOHC (P) Ford Escort: 1997, 1998, 1999, 2000, 2001, 2002.
  • 1.9L DOHC (3) Ford Escort ZX-2: 1997, 1998, 1999, 2000, 2001, 2002.
  • 1.9L SOHC Mercury Tracer: 1997, 1998, 1999.

What Causes Spark Plugs To Wear Out?

Every time you crank and start the engine, the spark plugs take a hit. The spark that jumps from the center to the side electrode slowly wears them down. It doesn't happen overnight, but it does every time the engine runs.

If you're using regular copper spark plugs, they typically last around 50,000 to 60,000 miles. Platinum-tipped spark plugs hold up much longer —close to 100,000 miles before you need to replace them.

Now, on a high-mileage engine, it's not just the normal wear and tear of daily driving wearing the them out. The leading cause of premature spark plug failure is carbon fouling.

This condition develops once the engine starts burning oil. The oil enters the combustion chamber and leaves heavy carbon deposits on the spark plug electrodes.

When carbon bridges the gap between the electrodes, the spark can no longer jump across. The result is a dead cylinder, which shows up as a misfire and a rough idle.

On the 1996 Escort/Tracer with OBD II, carbon-fouled plugs will usually trigger the PCM to flag the bad cylinder. You'll get a check engine light and a stored misfire code —usually P0300 to P0304.

When Should I Replace The Spark Plugs?

Deciding when to replace the spark plugs comes down to two key factors:

  1. The replacement interval specified in the owner's manual.
  2. The actual condition of the engine —especially if it has started burning oil.

The service interval in the owner's manual is based on ideal operating conditions: a healthy engine, no oil consumption, and the correct type of plug installed (copper or platinum). If the engine meets those conditions, the factory schedule is a reliable guideline.

However, once the engine starts burning oil, carbon fouling takes out the spark plugs much sooner —often before normal electrode wear shows up. In that case, you may be replacing them every few months just to keep it running smooth.

If your Escort or Tracer's engine is burning oil and the plugs are carbon-fouled to the point they no longer fire, you'll know it's time to replace them when you notice:

  • Rough idle at low RPM (such as when you're stopped at a traffic light).
  • The check engine light on, with a misfire code stored in the PCM's memory.

If you're not sure whether your Escort or Tracer's engine is burning oil, here are the telltale signs:

  • You're regularly adding engine oil just to keep the dipstick at the full mark.
  • You've got blue smoke coming out from the tailpipe (especially when you step on the gas).
  • You see blue smoke (out of the tailpipe) on startup, especially after your Escort (or Tracer) has been sitting for a while.

On the flip side, if the engine isn't burning oil, that's good news. In most cases, you'll get the full service life out of the spark plugs without premature fouling.

With copper spark plugs (the OEM type), expect to replace them at roughly 50,000 miles.

If you've installed platinum or iridium plugs, they'll last much longer —typically close to 100,000 miles before, you'll need to replace them.

Which Spark Plugs Should I Buy: Motorcraft Or Brand X?

From the factory, the 1.9L Ford Escort (or Mercury Tracer) came with Motorcraft copper spark plugs.

Since Motorcraft is the original equipment (OE) brand, using them at tune-up time guarantees you're installing the same type the engine was designed for.

That said, you're not limited to Motorcraft only. As long as the spark plugs you choose match the correct heat range and specifications for your 1.9L Escort or Tracer, any quality brand will perform properly.

Here's the part you'll want to be paying close attention to:

  • If the engine is burning oil, there's no benefit in paying extra for premium plugs. Go with low-cost copper plugs, since carbon fouling will short out any type once oil starts coating the electrodes. Brand name doesn't matter here either —you'll be replacing them frequently either way.
  • If the engine is not burning oil, upgrading to platinum plugs makes sense. They offer longer service life and more consistent performance. Any quality brand will do the job —sticking with Motorcraft is an option if you prefer OE, but it's not required.

Other Causes Of Spark Plug Failure

Like I've said before, when a spark plug fails to fire, the result is a cylinder misfire —no way around it.

From a diagnostic standpoint, the reasons a spark plug stops firing usually fall into two main categories:

1. Engine mechanical problems that end up fouling the spark plug with oil, fuel, or heavy carbon deposits.

Here are the key things to look for:

  • Oil fouling from worn piston rings or leaking valve stem seals, allowing oil into the combustion chamber and onto the spark plug.
  • A fuel injector stuck open, flooding its cylinder and leaving the plug wet with raw fuel.
  • A bad spark plug wire not delivering spark to its spark plug.
  • An bad ignition coil.
  • Low compression in one or more cylinders, leading to incomplete combustion and eventual spark plug fouling.

2. Installation mistakes —these are the kinds of errors that physically damage a spark plug or prevent it from firing correctly.

The most common examples include:

  • Over-tightening the spark plug, which can crack the ceramic insulator or damage the threads.
  • Dropping the spark plug before installation and creating a hairline fracture in the insulator.
  • Closing the spark plug gap accidentally while handling it, preventing the spark from jumping across the electrodes.
  • Installing the spark plug with an incorrect gap setting.
  • Washing the engine while it's still hot, causing thermal shock that cracks the spark plug's porcelain insulator —resulting in a misfire.

CASE STUDIES:

I've had the chance to diagnose and resolve quite a few cylinder misfires over the years (caused by installation errors). Here's a case study of one from a few years back:

Here's one that deals with low cylinder compression causing a cylinder misfire. This one I diagnosed on my brother-in-law's car:

In this last case study, the spark plug and spark plug wire had carbon tracks causing a cylinder misfire:

More 1.9L Ford Escort And Mercury Tracer Diagnostic Tutorials

You can find a complete list of 1.9L Ford Escort and Mercury Tracer tutorials in this index:

Here's a small sample of the tutorials you'll find in the index:

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