'This Is Why I Stopped Quoting Over The Phone:' Man Wants Mechanic To Change Out His Fuel Injectors. There’s Just One Problem

Car trouble can be deceptive. A noise or performance issue might sound familiar, but the real cause could be something entirely different.

Because of that uncertainty, mechanics prefer to handle the diagnosis themselves. They rely on training and diagnostic tools to pinpoint the issue accurately, rather than replacing parts based on guesswork.

Letting a professional investigate first usually saves money and ensures the repair actually solves the problem.

In a trending video with more than 22,000 views, diesel mechanic Jonathan (@Jsmalls_6.6), describes a frustrating experience he just had with a potential customer. 

“Alright, I’m gonna rant for a second,” Jonathan begins. 

He says the interaction started off normal enough with a customer calling to ask to have their truck towed to his shop because it “runs like [expletive]” and has “a mechanical knocking noise.” 

The caller speculates that it’s the injectors and asks how much it will cost to replace them.

Jonathan pushes back, asking the man if he wants him to look at the vehicle to figure out the root issue or “just throw injectors at it?” 

“Because if I just throw injectors at it and it doesn’t fix the issue, that’s on you,” Jonathan says.

When pressed for a price, Jonathan says he cannot give an exact quote without knowing more about the car, since at this point he doesn’t even know the make and model. 

The customer reveals his car has a 5.9 Cummins engine and Jonathan guesses that replacing the injectors on that would run about $4,000.

The caller seems shocked by the price and insists another shop quoted $3,200. Jonathan explains that additional work could be necessary once the truck is opened up.

“If there’s a mechanical noise, we throw injectors per your request,” he says. “While I’m there, I might as well adjust the valves. You’re looking at a new valve cover gasket. Who knows what else it’s gonna need while I’m in there, right?”

Despite the explanation, the caller says they’d take their car to the cheaper shop.

“Okay mother[expletive], I don’t give a [expletive]. Dude, seriously, you don’t even know what the [expletive] is wrong with your truck,” the mechanic replies.

Do You Need A Diagnostic Test?

Modern vehicles operate more like computers than traditional machines. As Marks Auto Service explains, onboard computers monitor nearly every system in a car, truck, or SUV, detecting errors long before a driver or mechanic might notice them.

Running a diagnostic test provides a full report of these systems, helping mechanics identify the root cause of an issue rather than guessing based on symptoms alone.

This is especially important when dealing with engine noises such as knocking. Engine knocking can indicate serious issues like low engine oil, engine bearing failure, or excessive crankshaft end-play, CarParts explains.

Even if a vehicle seems drivable, continuing to operate a car with a knocking engine can lead to extensive internal damage, potentially requiring costly repairs or a complete engine replacement.

Because engine knocking can stem from multiple sources, a proper diagnostic check ensures that mechanics address the actual problem. Without it, replacing parts like injectors alone may not fix the underlying issue and could result in wasted time and money.

A Common Experience

Jonathan’s post had self-described mechanics feeling his pain.

“So we all out here dealing with the exact same customers??” a top comment reads.

“They don’t get the option. We do NOT allow customers to dictate how we run our businesses. They either pay for the diagnostic testing and evaluation so we can test not guess or they aren’t a client,” a second wrote.

“As soon as I figure out someone is price shopping I’m out. Not gonna race to the bottom. if u can get it done cheaper I’m happy for u,” said a third.

Motor1 reached out to Jonathan for comment via TikTok direct message and comment. We'll update this if he responds.