Old timer called me a parts swapper to my face, and honestly he was right
Back in March I was working a 2012 Cummins in Boise that had a misfire no matter what I did. I threw injectors, a rail pressure sensor, and even a whole lift pump at it over three visits. This retired guy who used to wrench on semis watched me for like 20 minutes from the waiting room. He finally walked over and said, "You're swapping parts, son, not fixing a problem." He asked me to check the fuel return line for restrictions. Turns out a collapsed rubber hose was starving the rail at idle. That $12 hose fixed what I'd billed close to $1,600 in parts on. Has anyone else had a moment where an old-timer called out your process and it stuck with you for months?
Honestly the old guy got lucky, that's it. You can't sit here and act like checking a return line is some magic trick that beats doing actual diag work, because for every collapsed hose story there's ten more where the injectors really were shot and the guy who ignored them looked like a fool. Swapping parts gets a bad rap but sometimes it is the process, you test what you can and the fastest path is trying the known fixes on a truck with 200k miles. A $12 hose that fixes it after the fact is easy to brag about, nobody posts the times grandpa's advice wasted a whole day. And let's be real, watching from a waiting room for 20 minutes doesn't mean he knew the truck, he threw a guess and it landed.