Been torquing injector lines wrong for years until a smoke test showed me

I was working on a Duramax with a rough idle last week, and I was sure it was a bad injector. I pulled the lines, swapped a suspect one, and put it all back together. The problem got worse. I did a smoke test on the intake, and I saw a tiny wisp coming from the base of one of the lines I just touched. Turns out, I've been using the 'snug plus a quarter turn' method from an old boss, but on these newer high-pressure common rail systems, that's not enough. The spec is a specific torque, like 22 foot-pounds, and then a second angle torque. I was leaving them just a hair loose, enough to let in air under load. Felt like a real idiot... but at least I know now. Anyone else have a torque spec story that changed their routine?

3 comments

3 Comments

the_max27d ago

So you're saying the spec dropped from 22 to 18 foot-pounds? That's a huge detail that would totally mess you up. It makes me wonder how many other "standard" practices from older diesels are wrong on the new stuff. I bet a lot of guys are still using the old torque numbers because that's just what they've always done. The manuals really aren't optional anymore, you gotta check every time.

lily36027d ago

Robin's got a point about checking the manual. The spec changed around the LML generation. My L5P book calls for 18 ft-lbs on the primary torque, then a 30-degree final turn. Using the old 22 ft-lb number on the newer engines could actually overstress the fittings.

robin_wright27d ago

Wait, is that 22 foot-pounds for the Duramax? I thought the final torque on those was lower, like 18, then the angle turn. Might want to double-check the service manual for your exact year.