2019 Ford Transit Spark Plug Type & Gap Guide

As an ASE-certified master technician, I regularly see fleet vehicles like the 2019 Ford Transit roll into the bay for routine maintenance. Whether your Transit is hauling cargo, carrying passengers, or upfitted as a camper, keeping its ignition system in top shape is critical for fuel economy and power. Below is your comprehensive guide to selecting, gapping, and installing the correct spark plugs for your 2019 Ford Transit.

Quick reference

The 2019 Ford Transit is typically equipped with either the naturally aspirated 3.7L Ti-VCT V6 or the twin-turbo 3.5L EcoBoost V6. (Note: The 3.2L Power Stroke diesel utilizes glow plugs, not spark plugs). Here are the exact specifications you need:

*Tech Note: While Ford states 100,000 miles, turbo engines are notoriously hard on spark plugs. I strongly recommend checking/replacing EcoBoost plugs every 60,000 miles to prevent misfires under load.

Why the right plug matters

Modern engines are incredibly sensitive to spark plug design. Choosing the correct plug involves two main factors: heat range and electrode metallurgy.

• Heat Range: The heat range determines how fast the spark plug pulls heat away from its tip and transfers it to the cylinder head. The twin-turbo 3.5L EcoBoost generates immense combustion temperatures and requires a specific heat range to prevent pre-ignition (knock).
• Electrode Metal: Factory Motorcraft plugs for the Transit are Iridium. Iridium is much harder and more durable than platinum or traditional copper. It allows for a fine-wire electrode that requires less voltage to jump the gap while surviving the extreme pressures of the EcoBoost and the high mileage demands of the 3.7L. Never downgrade to copper or single-platinum plugs in these engines.

How to gap a spark plug

Even if a box says "pre-gapped," a good technician always verifies the gap before installation. A plug dropped in shipping can easily have its ground strap bent, closing the gap.

1. Use the right tool: Avoid cheap coin-style gappers, which can easily snap the fragile iridium tip. Use a wire-type feeler gauge.
2. Check the gap: Slide the correct size wire between the center electrode and the ground strap. It should slide through with a slight "drag."
3. Adjust if necessary: If the gap is too tight, use the bending tool on the gauge to slightly pull the ground strap up. If it's too loose, gently tap the ground strap on a soft wooden workbench. Never pry against the center iridium electrode.

Replacement procedure tips

Both the 3.7L and 3.5L engines in the Transit use a Coil-on-Plug (COP) ignition system. The engine bay in the Transit van is notoriously cramped, with the cowl hanging over the rear cylinders.

• Access: You will need a variety of extensions and a high-quality universal joint (swivel) socket to reach the rear cylinders. Take your time, and do not force the socket at a bad angle, which could crack the plug's porcelain.
• The Anti-Seize Debate: Ford specifically advises against using anti-seize on the threads of nickel-plated plugs (like modern Motorcraft plugs). Anti-seize acts as a lubricant, which alters torque readings and can lead to over-tightening and stripped aluminum cylinder head threads. Install them dry.
• Dielectric Grease: Always apply a small dab of dielectric grease to the inside of the ignition coil boot. This prevents moisture intrusion, stops high-voltage tracking (arcing), and ensures the boot won't fuse to the porcelain for the next guy who has to change them.

Known issues

While the 2019 Transit engines do not suffer from the infamous 3-valve 2-piece spark plug breakage that plagued older Ford 5.4L V8s, they have their own quirks.

The most common issue with the 3.5L EcoBoost is "spark blowout" under heavy acceleration. As plugs wear, the gap naturally widens. In a turbocharged engine, the dense air/fuel mixture creates high electrical resistance. If the gap is too wide, the spark can actually be "blown out" by the cylinder pressure, causing a harsh hesitation or misfire code (P0300-P0306). This is exactly why I recommend a tighter gap (0.030 in) and shorter replacement intervals for the EcoBoost.

Furthermore, always inspect the COP boots for carbon tracking (faint grey/black lines on the rubber). If a plug has been misfiring, the coil boot may be ruined. Replace the boots whenever you replace the plugs for cheap insurance.

Need plugs replaced? Find a shop on Repairius.