Pro tip: Found out the hard way that injector return lines can fool you...

Last Tuesday I was chasing a rough idle on a 2005 Cummins ISB. Compression was good, fuel pressure at the rail looked fine on the gauge. I swapped out the injectors one by one, no change. After 6 hours of scratching my head, an old hand named Mike walked over and pointed at the return lines. Said to pinch 'em off and watch the idle smooth out. Sure enough, the return line was cracked where it curves behind the block, letting air suck in. Cost me maybe 4 bucks for new hose and clamps, but I wasted a whole day and $200 on injectors I didn't need. Anybody else get burned by something that small on a common rail system?

2 comments

2 Comments

jade22611h ago

Buddy of mine had nearly the same thing happen on a Ford 6.0 a few years back. He was chasing a miss that came and went, swapped out a whole set of injectors and even put in a new FICM. Was about to pull the whole top end apart when his dad came over and saw the return line had a tiny rub spot where it touched the alternator bracket. Pinched it off with a clamp and the truck ran perfect. He was so mad he kicked the tire, lol. Cost him like 600 bucks in parts and three weekends for a 5 dollar hose. Always check the simple stuff first, man.

olivia_wilson9h ago

Nah I gotta disagree with the "check the simple stuff first" thing though. I mean yeah it worked out for your buddy but if you stop to check every little hose and wire every time you get a weird miss you'll never get anything fixed. Especially on a 6.0 where those injectors are known to fail randomly, swapping em is a legit move. You can't be out there pinching fuel lines on a hunch when 90% of the time it is the actual parts failing. Sometimes you just gotta throw parts at it and move on, you know?