A Guide to Spark Plugs for the 1978-1986 Ford Fiesta
Keep your classic Fiesta's Kent engine firing on all cylinders with the right set of spark plugs.
- Stick to standard copper-core spark plugs from reputable brands like NGK, Denso, or Motorcraft.
- Do not waste money on expensive iridium or platinum plugs; they offer no benefit for this engine.
- Always verify the spark plug gap is set to approximately 0.035 inches before installation.
- This is a very easy and inexpensive DIY job that can be completed in under 30 minutes with basic tools.
Symptoms of Failing Spark Plugs in a First-Gen Fiesta
The simple ignition system in the 1978-1986 Ford Fiesta relies on healthy spark plugs. When they start to wear out, you'll notice. The signs are usually straightforward and shouldn't be ignored.
- Rough Idling: The engine may shake or sound uneven when the car is stopped.
- Engine Misfires: You might feel a hesitation or stumble from the engine, especially when accelerating.
- Reduced Fuel Economy: If you're filling up the tank more often, weak or fouled plugs could be wasting fuel.
- Difficulty Starting: A weak spark makes it harder for the engine to fire up, particularly in cold or damp weather.
- Loss of Power: The car may feel sluggish and slow to accelerate because the fuel isn't burning completely.
A Note on Ford Spark Plug Issues
You may have heard about major spark plug problems on some Ford trucks and SUVs with Triton V8 engines, where plugs could break or blow out of the cylinder head. Be assured, this issue does not affect the 1.6L Kent engine in your 1978-1986 Fiesta. Your vehicle uses a completely different and much simpler engine design.
Choosing the Right Aftermarket Spark Plugs
For the Kent engine in your Fiesta, you do not need expensive, fancy spark plugs. This engine was designed for simple, reliable copper-core spark plugs. Modern iridium or platinum plugs offer a longer life but provide no real performance benefit for this application and are not worth the extra cost. Stick with standard plugs from a trusted brand.
Brand Quality Tiers
- OEM & Premium Aftermarket (NGK, Denso, Motorcraft): Motorcraft was the original equipment (OEM) brand for your Fiesta. NGK and Denso are Japanese brands with a stellar reputation for quality and reliability, often considered equal to or better than OEM. Plugs like the NGK BPR6ES are a common, reliable choice for the Kent engine.
- Standard Aftermarket (Autolite, Bosch, Champion): These are well-known brands that have been around for decades. They offer dependable, budget-friendly copper plugs that are perfectly suitable for the Fiesta's engine. Champion N6YC is a standard plug specified for the Ford Kent engine.
- Economy Brands (Skyward): These are typically private-label or budget brands. While they will work, their quality control and lifespan may not match the more established manufacturers. They are an acceptable choice if the budget is the primary concern.
Always Check the Gap!
No matter which brand you choose, you must check the spark plug gap before installation. The correct gap for a standard 1.6L Kent engine is typically around 0.035 inches (0.9mm). Use a feeler gauge or gap tool to verify this measurement. An incorrect gap can cause misfires and poor performance.
Cost of Replacing Ford Fiesta Spark Plugs
Replacing spark plugs on this vehicle is one of the most affordable maintenance jobs you can do.
| Part Type | Price Range (Set of 4) |
|---|---|
| New OEM (Motorcraft) | $12 - $25 |
| New Aftermarket | $15 - $82 |
| Shop Labor | $50 - $100 |
Frequently Asked Questions
How often should I change the spark plugs on my 1978-1986 Fiesta?
For a classic car with standard copper spark plugs, a good interval is every 15,000 to 30,000 miles, or every 2-3 years, whichever comes first. Since it's an easy and inexpensive job, doing it more frequently is good preventative maintenance.
Is it hard to replace the spark plugs myself?
No, this is a very easy job for a DIY mechanic. The spark plugs are easily accessible on top of the engine. You only need a few basic tools like a ratchet, an extension, and a spark plug socket. The entire job can be done in under 30 minutes.
What is a spark plug 'heat range'?
The heat range refers to how quickly the spark plug tip dissipates heat. For a stock Fiesta engine used for daily driving, you must use the standard, factory-recommended heat range. Using a 'colder' plug is only necessary for highly modified or racing engines and can cause carbon fouling in a standard engine.
Are there any recalls or TSBs for my Fiesta's spark plugs?
No, there are no known recalls or Technical Service Bulletins (TSBs) from Ford or the NHTSA related to spark plugs for the 1978-1986 Ford Fiesta.
Technical Specifications
OEM Part Numbers: SP447A
Engine: 1.6L Ford Kent (Crossflow) Plug Type: Standard Copper Core Common Part Numbers: NGK BPR6ES, Champion N6YC Thread Size: 14mm Hex Size: 13/16" or 21mm Recommended Gap: 0.035" (0.9mm)
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.