Chased a phantom misfire for 6 hours, turned out to be a bad ground strap

Hauled a 2019 Freightliner into the shop last Tuesday. Driver said it was missing hard under load, throwing no codes. I replaced the fuel filters, checked injector return rates, went through the whole intake path. Six hours in, I finally noticed the ground strap from the block to the frame was cracked right where it bolts up. Cleaned it, tightened it, fired it up and it ran perfect. That little strap stole half my day. How many of you have burned hours on electrical gremlins that turned out to be simple grounds?

2 comments

2 Comments

sanchez.julia3d ago

Six hours in" just made my eye twitch, no joke. I had a similar one on a Peterbilt where the cab lights would flicker like a rave and I chased it for two full afternoons. Turns out the ground bolt behind the battery box was corroded so bad it looked like it had been sitting in a salt bath for years. You really do check everything else first, the filters, the sensors, the wiring harness, and it's always the dumb little strap or bolt that costs you the whole shift. I swear they should teach "check grounds first" in diesel school before they even let you touch a multimeter. That cracked strap is the kind of thing you'd walk right past a hundred times too, so I totally get how it ate your Tuesday.

ray_burns3d ago

Man, you're not wrong about the ground bolt thing. I learned that lesson the hard way on an old Freightliner, spent a whole day chasing a no-start that turned out to be a frame ground that looked fine until you wiggled it just right. They really should drill that into your head day one, would've saved me a lot of cuss words and skin off my knuckles.