Air + fuel
Air filter → MAF → throttle → intake manifold → cylinder. Fuel pump → rail → injector. The ECM commands injector pulse width based on MAF + O2 + temp + rpm.
Modern engines are 8–10 systems working in sync. Knowing the boundaries between them is the difference between guessing and diagnosing.
Most misdiagnoses cross system boundaries — a 'fuel problem' is really an air leak, an 'electrical issue' is really a ground.
Air filter → MAF → throttle → intake manifold → cylinder. Fuel pump → rail → injector. The ECM commands injector pulse width based on MAF + O2 + temp + rpm.
Coil-on-plug or distributorless ignition; spark plugs at 30–100K mi service. Diesel: compression ignition, no spark — fuel timing is everything.
Pressurized oil to bearings + turbo; cooling system maintains 195–220°F; exhaust scavenges combustion gases and feeds aftertreatment.
Diesel needs more frequent fuel filter changes, has aftertreatment (DPF/SCR), uses heavier oil, and benefits from longer warm-up — but lasts 2–4x longer.