Old timer at the shop made me rethink how I test injectors

Had a guy push 70 come by my bay last Thursday. He watched me pull a set of injectors and go straight for the pop tester. He just shook his head and said I was wasting time checking pressure if I hadn't looked at the spray pattern first. So I tried it his way on a 5.9 Cummins that had a rough idle. Sure enough, two injectors looked fine on the gauge but had a uneven spray. Fixed it in under an hour instead of chasing ghosts all day. Anyone else been shown up by some old school trick that actually works better?

3 comments

3 Comments

margaretm231mo ago

Yeah, 'spray pattern over pressure' is the kinda thing that makes you stop and think..." I had an old diesel mechanic tell me once that the best way to check an injector was to listen to it pop, not look at the gauge. Said he could hear a bad spray pattern before he even saw it... turns out he was right about half the time anyway. Just goes to show you, sometimes the old guys learned tricks that skip right past all the fancy numbers.

jadew631mo ago

So how do you actually tell the difference by ear? Like is it a sharper pop vs a duller sound or more about the rhythm of the pops? I've heard old guys talk about hearing misfires through a screwdriver on the valve cover but never tried it myself. Seems like one of those skills you gotta develop over years not just read about.

felixfisher1mo ago

Wait are you saying spray pattern matters more than pressure numbers? I used to be all about the gauge readings but this makes me want to try looking at the spray first next time.