Father-son mechanics stumped by issue on nearly-new Mazda, then they open the hood and find something that shouldn’t be there yet

A father-and-son mechanic team found a serious and costly problem on a 2023 Mazda CX-5 that’s only two years old. They discovered heavy carbon buildup on the fuel injectors, which caught them off guard since the car is nearly brand new.

According to Motor1, the mechanics, who run Royalty Auto Service, were confused at first because they didn’t expect such a big issue on a recent model. However, the car wasn’t exactly low on miles. The Mazda SUV already had 96,588 miles on it, which is way more than normal for a two-year-old car. Still, the mechanics say this problem shouldn’t be showing up yet.

The shop warned viewers that this type of failure is becoming more common each year. When they ran tests, everything seemed fine until they checked the long-term fuel trims. The data showed the trim was maxed out at 25%, which is a major warning sign.

Carbon buildup is clogging up engines faster than expected

When the fuel trim maxes out, it means the engine is getting too much air and not enough fuel. The car’s computer tries to fix this by adding more fuel, but once it reaches that 25% limit, it can’t add any more.

That’s when the mechanics opened the hood and found the problem: the fuel injectors were completely black. “There’s some carbon buildup on there,” one mechanic said in their video, which got over 113,200 views on TikTok. He said they tried cleaning the injectors, but “it didn’t help.” He also mentioned they saw the same issue on a Ford a few weeks earlier. Like other costly repair issues mechanics frequently encounter, this problem requires expensive parts replacement.

This is bad news for the owner because replacing clogged injectors costs a lot of money. The mechanic’s solution was simple but important: “If you’re not running top-tier fuel, you need to run it.”

Fuel injectors spray fuel into your engine through tiny holes. When you use cheap gas with fewer cleaning agents, those small holes get clogged with carbon over time. The engine runs “lean” because the dirty injectors can’t spray enough fuel, creating too much air in the mix. The car’s computer sees this problem and tries to fix it by increasing fuel delivery, pushing the trim number up to 25%.

Fuel injectors normally last between 50,000 and 100,000 miles, or sometimes the life of the vehicle. Cleaning them every 25,000 to 30,000 miles should help. Most car owners never have to replace them if they maintain their vehicle properly. Top-tier gas helps prevent this mess because it has extra cleaning additives that keep injectors clean. Regular maintenance can help drivers avoid unexpected discoveries during routine vehicle inspections.