2014 Isuzu NPR Spark Plug Type & Gap Guide

Keeping your 2014 Isuzu NPR on the road is vital for your business. Whether you are running delivery routes or hauling equipment, a misfire can cost you time and money. While Isuzu is famous for its diesel engines, the gas-powered 2014 Isuzu NPR utilizes the robust General Motors 6.0L Vortec V8 (L96). Because this is a heavy-duty commercial application, using the correct spark plugs and adhering to exact specifications is critical for optimal fuel economy and engine longevity.

Quick reference

Note: The original ACDelco 41-110 plug has been superseded by ACDelco 41-162.

Why the right plug matters

In a commercial vehicle like the NPR, heat range and electrode materials are incredibly important. The GM 6.0L V8 works extremely hard moving a heavy cab-over chassis, generating significant combustion chamber heat.

• Heat Range: Running a plug that is too hot can lead to pre-ignition and catastrophic engine damage, while a plug that is too cold will foul out prematurely. Sticking to the OEM heat range ensures the plug tip stays clean without overheating.
• Electrode Metal: Standard copper plugs conduct electricity well but wear out fast. Platinum offers a middle ground. However, Iridium is the gold standard here. The OEM ACDelco plugs are iridium-tipped, which allows them to withstand the rigorous duty cycle of a commercial truck and last up to 100,000 miles.

How to gap a spark plug

Even if your iridium spark plugs claim to be "pre-gapped" out of the box, it is a cardinal rule for technicians to verify the gap before installation. Shipping drops can easily close the gap.

1. Use the right tool: Use a wire-style gap gauge or a feeler gauge. Coin-style gauges can easily snap the brittle center electrode of an iridium plug.
2. Measure: Gently slide the 0.040" wire between the center and ground electrodes. It should have a slight drag.
3. Adjusting (Light Bend): If the gap is too tight, use the bending tool on your gauge to gently pull the ground strap back. Never pry against the center iridium tip—it will fracture instantly.

Replacement procedure tips

The 6.0L V8 in the Isuzu NPR uses a coil-near-plug ignition system. Instead of the coil sitting directly on the spark plug, ignition coils are mounted to the valve covers, and short spark plug wires connect them to the plugs.

• Wire Removal: Twist the spark plug boot side-to-side before pulling to break the heat seal. Do not yank the wire itself, or you will pull the terminal right off the core.
• The Anti-Seize Debate: GM advises against using anti-seize on the threads of their ACDelco plugs. These plugs come with a special nickel coating designed to prevent galling in the aluminum cylinder heads. Adding anti-seize acts as a lubricant, which can easily cause you to over-torque the plug and strip the threads.
• Dielectric Grease: Apply a small dab of dielectric grease to the inside of the spark plug wire boots. This prevents moisture intrusion and ensures the boots will come off easily during the next 100,000-mile service.

Known issues

While you won't face the infamous 2-piece plug breakage found on older Ford 3-valve engines, the GM 6.0L V8 has its own quirks.

The biggest hurdle is the factory spark plug wires and heat shields. The metal heat shields surrounding the spark plug boots tend to rust and seize onto the spark plug shell due to the high temperatures of the exhaust manifolds. It is incredibly common for the spark plug wires to tear when attempting to remove them from a high-mileage fleet vehicle. As a master technician, I highly recommend ordering a replacement set of spark plug wires alongside your spark plugs to avoid leaving your truck stranded in the bay.

Need plugs replaced? Find a shop on Repairius.