2017 Isuzu NPR Spark Plug Type, Gap & Torque Guide

The 2017 Isuzu NPR gas truck is a reliable workhorse, powered almost exclusively by General Motors' robust 6.0L L96 Vortec V8 engine. Because this heavy-duty commercial truck is often subjected to severe driving conditions—long idle times, heavy payloads, and stop-and-go delivery routes—maintaining a healthy ignition system is critical. As an ASE-certified master technician, I can tell you that using the correct spark plugs and installing them to spec will keep your NPR running smoothly and prevent costly downtime.

Here is everything you need to know about replacing the spark plugs on your 2017 Isuzu NPR gas model.

Quick reference

Why the right plug matters

Commercial trucks require durable ignition components. The GM 6.0L V8 in your Isuzu NPR comes from the factory with iridium spark plugs. Iridium is significantly harder and more durable than platinum or standard copper, allowing the electrode to be manufactured to a finer wire size. This fine wire concentrates the electrical charge, requiring less voltage to jump the gap and providing a more complete combustion event.

Using standard copper or lower-grade platinum plugs in this engine will result in a severely reduced lifespan—often failing before 30,000 miles—and can trigger misfire codes (P0300) under heavy load. The heat range is equally vital; using a plug that runs too hot can cause pre-ignition and engine knock, while a plug that runs too cold will quickly foul out during the extensive idling common with delivery trucks. Stick to the ACDelco 41-162 or equivalent premium iridium plugs from NGK or Denso.

How to gap a spark plug

Even though modern iridium spark plugs for the 6.0L V8 come pre-gapped from the factory at 0.040", they should always be verified before installation. A plug can easily be dropped in transit, closing the gap.

1. Use a wire-style gauge: Avoid using a coin-style ramp gauge on iridium plugs. The fragile iridium center electrode can snap under lateral pressure. Use a wire-style feeler gauge instead.
2. Measure gently: Slide the 0.040" (1.01 mm) wire through the gap. It should pass through with a light drag.
3. Adjust with a tool: If the gap is too tight, use the bending notch on your gapping tool to gently pull the ground strap upward. Never lever the tool against the delicate center electrode.

Replacement procedure tips

The 2017 Isuzu NPR 6.0L V8 utilizes a coil-near-plug setup. Each cylinder has its own ignition coil mounted on the valve cover, connected to the spark plug via a short spark plug wire with a metal heat shield.

• Wire removal: The spark plug wires on this engine can bake onto the spark plug over 100,000 miles. Twist the boot back and forth before pulling to break the seal.
• The anti-seize debate: Modern ACDelco and NGK spark plugs feature a specialized zinc or nickel plating on the threads designed to prevent seizing in the aluminum cylinder heads. Do not use anti-seize compound! Adding liquid or paste to the threads acts as a lubricant, which alters the friction coefficient and often leads to over-torquing and broken plug shells.
• Dielectric grease: Apply a small dab of dielectric grease to the inside of the spark plug wire boot before reinstalling. This prevents moisture intrusion, stops high-voltage tracking, and ensures the boot won't fuse to the porcelain of your new plug.
• Torque properly: Always use a torque wrench. 11 lb-ft (15 Nm) is all it takes to crush the gasket properly. Over-tightening can strip the aluminum threads in the cylinder head.

Known issues

While you won't face the dreaded two-piece broken spark plug issues common to older Ford 3-valve engines, the GM 6.0L in the NPR has a couple of quirks.

First, the metal heat shields on the spark plug wires are notorious for degrading or causing cuts in the wire insulation over time, leading to a spark jumping to the exhaust manifold. If you are changing the plugs at 100,000 miles, it is highly recommended to replace the spark plug wires simultaneously.

Second, access to the rear spark plugs can be slightly constrained depending on the cab configuration, but the tilt-cab design of the Isuzu NPR usually makes this much easier than servicing the same engine in a traditional van or pickup.

Need plugs replaced? Find a shop on Repairius.