Chasing a misfire for 2 days, turned out to be a $9 ground strap

Spent all weekend on a 2012 F-150 that kept throwing P0303 codes in the bay, swapped coil packs, plugs, even did a compression test up in the Rockford shop. Finally got out the old scope and saw the waveform was fine, but the block ground strap was corroded clean through near the firewall. A $9 part from Napa fixed it after I'd already billed the customer for 6 hours of diag time, you know that hurt to walk back. Anyone else ever have a ground issue that drove you nuts before you caught it?

1 comments

Log in to join the discussion

Log In

1 Comment

jesse_miller22d ago

Man that corroded ground strap near the firewall is such a kick in the teeth after all that work. I feel you on the P0303 rabbit hole, those misfire codes love pointing you at coils and plugs when the real problem is hiding somewhere dumb like a ground. Had a similar thing on an old Silverado where the body ground was green and fuzzy and it made the whole dash act haunted, gauges bouncing around like crazy. You did the right thing not charging the customer for a wrong call, even if it stung. At least you got smart and grabbed the scope instead of throwing more parts at it, that move alone saves you next time.

2