P0284

P0284 is the cylinder 8 contribution/balance fault — V8 or larger only. The ECM has determined that cylinder 8 is deviating from the per-cylinder fuel trim average by more than +/- 5 mm3/stroke for a sustained period, meaning either the cylinder is making less torque than commanded (weak compression, restricted injector, valve issue) or more torque than commanded (stuck-open injector, leaking high-pressure fuel seal feeding extra fuel). On Ford modular V8s and Powerstroke V8s, cylinder 8 lives at the rear of the left bank closest to the firewall and transmission bellhousing — physically the hardest cylinder to reach on a 4WD F-Series. On GM LS-series V8s and Duramax V8s, cylinder 8 is also rear left bank. Cheapest-first ladder: live cylinder balance trims first (normal 0-3, flagged greater than 5), cutout test second (healthy 80-150 RPM drop, weak less than 50), compression test third (less than 85% of highest cylinder is mechanical), injector electrical and back-leak fourth. On diesel V8s also check the glow plug current draw on cyl 8 — a partially shorted glow plug skews combustion temp and creates a contribution fault that mimics injector failure. Expensive-misdiagnosis caveat: on Duramax engines specifically, a failing CP4.2 high-pressure pump can shed metal that lands in the rear-most injectors (cyl 7 and cyl 8) first because of fuel rail flow geometry — if you replace cyl 8's injector without inspecting the rail and pump, you'll destroy the new $400-$800 injector within months.

Vehicle-specific patterns: 2001-2004 GM Duramax LB7 6.6L throws P0284 paired with other balance codes from the well-known LB7 injector failure (cup-style injectors crack and leak fuel into the valve cover oil); GM extended warranty to 200k miles on LB7 injectors and the standard fix is replacing all 8. 2008-2010 Ford 6.4L Powerstroke V8 throws P0284 from piston cracking, oil-cooler restriction, and EGR-cooler contamination — left-bank cylinders fail first because of cooling flow geometry. 2011-2016 Duramax LML 6.6L throws P0284 from CP4.2 pump failures sending metal contamination through the rail and damaging the rear injectors. 2008-2013 BMW N63 4.4L V8 (550i, 750i, X5/X6 5.0i) throws P0284 alongside P0281/P0275 in clusters when injectors and coils degrade as a set; BMW's N63 Customer Care Package covers most affected VINs. 2010-2017 Audi 4.2L V8 FSI throws P0284 from carbon buildup on intake valves of the rear-bank cylinders; walnut-blast service resolves it. Estimated repair: $300 (intake valve walnut blast) to $9,000 (full pump + rail + injector set on a Duramax CP4.2 failure).