{"model": "claude-web", "provider": "Claude web app (claude.ai), signed in on a paid Max plan, Opus 5.5, default settings", "task": "auto-diag", "prompt": "Write a step-by-step diagnostic walkthrough for high school automotive students: a 2012-2018 gasoline car comes in with a check engine light and code P0300 (random/multiple cylinder misfire). Show the logical order of tests from simplest to most involved, what tools are needed, what each result means, and safety notes. Format it as a student handout.", "ran_at": "2026-10-17T13:18:54-0700", "output": "Claude Opus 5.5\n\nI'll put together a printable student handout as a doc, walking through P0300 diagnosis from simplest to most involved.\n\nOutline's up; now writing the overview.\n\nNow the safety rules.\n\nNow the tools list.\n\nNow the main step-by-step procedure.\n\nNow the quick-reference table.\n\nLast, the student worksheet.\n\n[P0300 Misfire Diagnosis \u2014 Student Handout](https://claude.ai/code/artifact/71458a4f-4819-44e3-9898-4b3a2a81023f) is ready. You can edit it inline, comment on it, or export it as a PDF to print.\n\n----- ARTIFACT CONTENT (Claude Docs: \"P0300 Misfire Diagnosis \u2014 Student Handout\") -----\n\nP0300 Misfire Diagnosis \u2014 Student Handout\nOct 17, 2026 \u00b7 @Leon\nOverview\nP0300 means the engine computer (PCM) has seen misfires that are random or spread across more than one cylinder. It tells you what is happening, not why. Your job is to find the cause by testing in order: cheap and quick first, invasive and time-consuming last.\nScenario: A 2012\u20132018 gasoline car arrives with the check engine light (MIL) on. The scan tool shows P0300. The customer says it \"runs rough sometimes.\"\nHow the PCM sees a misfire: It watches crankshaft speed through the crank position sensor. Each cylinder firing gives the crank a small push. When a cylinder fails to fire, the crank slows for an instant, and the PCM counts it. Too many counts in 200 or 1,000 revolutions sets a code.\nA misfire needs one of three things to be missing:\n1. Spark \u2014 plugs, coils, wiring\n2. Fuel (correct air-fuel mix) \u2014 vacuum leaks, fuel pressure, injectors, MAF sensor\n3. Compression \u2014 valves, rings, head gasket, cam timing\nWhen misfires hit several cylinders at random, think first about something all cylinders share: a vacuum leak, low fuel pressure, a bad MAF, bad fuel, or timing.\nBy the end of this lab you should be able to:\n\u2022 Retrieve codes, freeze frame and live data with a scan tool\n\u2022 Interpret fuel trims and misfire counters\n\u2022 Choose the next test based on the last result\n\u2022 Verify a repair before releasing the car\nSafety first\nRead these before you touch the car. Your instructor must approve any test marked (Instructor) in the procedure.\n\u2022 Flashing check engine light = stop driving. A flashing MIL means a misfire bad enough to overheat and destroy the catalytic converter. Do not road test until the cause is fixed.\n\u2022 Eye protection at all times. Fuel, coolant and cleaners can spray.\n\u2022 Exhaust gas kills. Run the engine only with an exhaust extraction hose attached or in a well-ventilated bay.\n\u2022 Secure the car. Parking brake on, transmission in Park (or Neutral for manual), wheels chocked.\n\u2022 Hot parts. Exhaust manifolds and catalytic converters exceed 500 \u00b0F. Let the engine cool before removing spark plugs \u2014 pulling plugs from a hot aluminum head can damage threads.\n\u2022 High voltage. Ignition coils produce 20,000\u201340,000+ volts. Never hold a plug wire or coil while cranking. Use an insulated spark tester, not your hand or a screwdriver.\n\u2022 Fuel is a fire hazard. No sparks or open flame. Know where the fire extinguisher is. Relieve fuel pressure before opening any fuel line, and wrap fittings in a shop rag.\n\u2022 Direct injection (GDI) danger. Many 2012\u20132018 engines have direct injection with fuel rail pressure over 2,000 psi. Never open the high-pressure side. Read GDI pressure only on the scan tool.\n\u2022 Moving parts. Keep hands, hair, sleeves and tools clear of belts and fans. Electric cooling fans can start with the key off.\n\u2022 Disable fuel and ignition for cranking tests (compression test) by pulling the correct fuse or relay per service information.\n\u2022 Use service information. Specs, firing order and procedures vary by vehicle. Look them up; don't guess.\nTools and equipment\nTool\nUsed in step\nWhat it tells you\nService information (repair manual, TSB database)\n1, all\nSpecs, firing order, known problems\nOBD-II scan tool with live data\n2, 4, 11\nCodes, freeze frame, fuel trims, misfire counters\nFlashlight and inspection mirror\n3\nCracked hoses, damaged wiring, leaks\nSmoke machine (or instructor-approved method)\n5\nLocation of vacuum leaks\nSpark plug socket, ratchet, extensions, torque wrench\n6\nPlug removal and correct reinstall torque\nSpark plug gap gauge\n6\nElectrode wear\nAdjustable spark tester\n6\nWhether a coil can produce strong spark\nDigital multimeter (DMM)\n6, 8\nVoltage, resistance, power and ground checks\nMAF sensor cleaner\n7\nRemoves contamination from MAF wire\nFuel pressure gauge kit (port injection only)\n8\nLow-side fuel pressure and hold\nNoid light set\n8\nWhether the PCM is pulsing an injector\nCompression tester\n9\nCylinder sealing (rings, valves, gasket)\nCylinder leakage tester and shop air\n10\nWhere compression is escaping\nFender covers, safety glasses, gloves, exhaust hose\nAll\nProtects you and the car\nStep-by-step diagnosis\nWork in order. After each step, write down what you found and decide whether it explains the misfire. Don't replace parts until a test proves they are bad.\nStep 1 \u2014 Talk to the customer and research\nTools: Repair order, service information.\n\u2022 Ask: When did it start? Cold or warm engine? Idle, cruising or accelerating? Was the light ever flashing? Recent fuel fill-up or repairs?\n\u2022 Look up Technical Service Bulletins (TSBs) for this make, model and engine. Many misfires are known factory issues with a published fix.\nWhat it means: A misfire only when cold points toward carbon buildup or a vacuum leak that seals when warm. A misfire right after fueling points toward bad fuel. A matching TSB may save hours.\nStep 2 \u2014 Scan for codes and freeze frame\nTools: OBD-II scan tool.\n\u2022 Record every code, not just P0300. Do not clear codes yet.\n\u2022 Record the freeze frame: RPM, engine load, coolant temp, vehicle speed, fuel trims.\n\u2022 Check Mode $06 (or the misfire counter screen) for per-cylinder misfire counts.\nWhat it means:\n\u2022 P0300 plus P0171/P0174 (system lean) \u2192 think air leak, MAF or fuel delivery. Go to Steps 4\u20135 and 7\u20138.\n\u2022 P0300 plus P0301\u2013P0308 \u2192 the misfire favors certain cylinders. Focus on those in Step 6.\n\u2022 P0300 plus P0016\u2013P0019 (cam/crank correlation) \u2192 possible timing chain stretch or VVT fault. Go to Step 10.\n\u2022 P0300 plus MAF, O2 or coolant sensor codes \u2192 diagnose that sensor first; it may be causing the misfire.\n\u2022 Freeze frame shows idle, warm engine \u2192 vacuum leak likely. High load \u2192 weak spark or low fuel pressure likely.\nStep 3 \u2014 Visual inspection\nTools: Flashlight, mirror, fender covers.\n\u2022 Engine off and cool. Check engine oil level and condition, and coolant level.\n\u2022 Inspect vacuum hoses, PCV hose, intake boot (between MAF and throttle body) for cracks, splits or loose clamps.\n\u2022 Inspect coil and injector connectors and wiring for damage, corrosion or rodent chewing.\n\u2022 Look for oil or coolant in spark plug wells.\nWhat it means: A torn intake boot or cracked PCV hose is a very common cause of random misfires. Low coolant with no visible leak may mean a head gasket problem (see Step 9). Oil in plug wells means leaking valve cover tube seals, which can short out coils.\nStep 4 \u2014 Read live data: fuel trims and sensors\nTools: Scan tool. Engine at operating temperature, exhaust hose on.\n\u2022 Watch short-term (STFT) and long-term fuel trim (LTFT) for each bank. Add them for total trim.\n\u2022 Record trims at idle, then hold the engine at 2,500 RPM.\n\u2022 Watch live misfire counters for each cylinder.\n\u2022 Check MAF reading (grams per second) and coolant temperature sensor reading.\nWhat it means:\n\u2022 Total trim within about \u00b110% \u2192 normal. Air-fuel mixture is probably not the problem; go to Step 6 (ignition).\n\u2022 Total trim above +10% at idle but closer to normal at 2,500 RPM \u2192 vacuum leak. Go to Step 5.\n\u2022 Total trim positive at all speeds, worse under load \u2192 fuel delivery or MAF reading low. Go to Steps 7\u20138.\n\u2022 Total trim strongly negative (rich) \u2192 leaking injector, high fuel pressure or a sensor reading wrong. Go to Step 8.\n\u2022 Coolant temp shows cold when engine is hot \u2192 bad ECT sensor; PCM is fueling incorrectly.\n\u2022 Misfire counts move around between cylinders \u2192 shared cause (air, fuel, timing). Counts stay on one or two cylinders \u2192 that cylinder's coil, plug, injector or compression.\nStep 5 \u2014 Test for vacuum leaks\nTools: Smoke machine. (Instructor)\n\u2022 Engine off. Follow the smoke machine instructions to fill the intake with smoke.\n\u2022 Look and use a flashlight for smoke escaping at hoses, gaskets, the throttle body, PCV valve and brake booster hose.\nWhat it means: Smoke escaping = air entering the engine unmeasured, making the mixture lean. Repair the leak and recheck fuel trims (Step 4). No smoke \u2192 the intake is sealed; move on.\nStep 6 \u2014 Check the ignition system\nTools: Plug socket, gap gauge, torque wrench, adjustable spark tester, DMM.\n\u2022 Engine cool. Remove coils and spark plugs, keeping them in cylinder order.\n\u2022 Read each plug: worn or wide gap, oil fouling, carbon fouling, cracked insulator, or white/blistered tip (overheating).\n\u2022 Check plug replacement history. Many engines call for new plugs around 60,000\u2013100,000 miles.\n\u2022 Coil swap test: if misfires stay on specific cylinders, swap a suspect coil to a different cylinder. Clear counters and run the engine.\n\u2022 Use the adjustable spark tester to confirm each coil fires strongly.\nWhat it means:\n\u2022 All plugs worn or gapped wide \u2192 replace the full set; worn plugs can misfire several cylinders at random.\n\u2022 Oil-fouled plug \u2192 oil entering that cylinder (rings or valve seals); note it for Step 9.\n\u2022 Misfire follows the coil to the new cylinder \u2192 that coil is bad. Misfire stays put \u2192 the problem is the plug, injector or compression in that cylinder.\n\u2022 Weak or no spark on the tester \u2192 check coil power and ground with the DMM before condemning the coil.\nStep 7 \u2014 Check the MAF sensor\nTools: Scan tool, MAF cleaner.\n\u2022 Inspect the MAF and air filter. Look for dirt, oil from an aftermarket oiled filter, or debris.\n\u2022 Compare the MAF reading at warm idle to specification. A common rule of thumb: about 1 g/s for each liter of engine size (a 2.0 L engine \u2248 2 g/s at idle).\n\u2022 Clean only with MAF-specific cleaner. Never touch the sensing wire.\nWhat it means: A MAF reading low makes the PCM add too little fuel \u2192 lean misfire on all cylinders, especially under load. If cleaning brings the reading and trims back to normal, recheck after a test drive.\nStep 8 \u2014 Check fuel delivery and injectors\nTools: Fuel pressure gauge (port injection only), noid light, scan tool. (Instructor)\n\u2022 Port fuel injection: connect the gauge to the test port. Check pressure at key-on, idle and snap throttle. Turn engine off and watch whether pressure holds.\n\u2022 Direct injection (GDI): read low-side and high-side pressure on the scan tool only. Compare desired vs. actual.\n\u2022 Use a noid light at an injector connector to confirm the PCM is pulsing it.\n\u2022 Ask about fuel quality: water, wrong fuel, a very old tank of gas.\nWhat it means:\n\u2022 Pressure low \u2192 weak fuel pump, clogged filter or bad regulator. Lean misfire under load.\n\u2022 Pressure drops quickly after shutoff \u2192 leaking injector, check valve or regulator. Rich trims or hard starting.\n\u2022 GDI actual pressure won't follow desired \u2192 high-pressure pump or sensor problem.\n\u2022 Noid light doesn't flash \u2192 wiring or driver problem, not the injector itself.\nStep 9 \u2014 Compression test\nTools: Compression tester, plug socket. (Instructor)\n\u2022 Engine warm, then shut off. Disable fuel and ignition per service information. Remove all plugs.\n\u2022 Hold throttle wide open. Crank each cylinder 4\u20136 compression strokes. Record the highest reading.\n\u2022 If a cylinder is low, add a teaspoon of engine oil to that cylinder and retest (\"wet test\").\nWhat it means:\n\u2022 All cylinders close to each other (commonly within 10\u201315%) and at spec \u2192 mechanical condition is OK.\n\u2022 One low cylinder, rises with oil \u2192 worn piston rings.\n\u2022 One low cylinder, no change with oil \u2192 valve not sealing or head gasket.\n\u2022 Two side-by-side cylinders low \u2192 head gasket leak between them.\n\u2022 All cylinders low and even \u2192 possible cam timing problem. Go to Step 10.\nStep 10 \u2014 Leak-down test and cam timing\nTools: Cylinder leakage tester, shop air, scan tool, service information. (Instructor)\n\u2022 Bring the cylinder to top dead center on its compression stroke. Hold the crank so it can't turn. Apply air and read the percentage of leakage.\n\u2022 Listen and look for where the air escapes.\n\u2022 Check cam/crank correlation data on the scan tool. Compare to specification for timing chain stretch.\nWhat it means:\nAir escaping from\nProblem\nThrottle body / intake\nIntake valve not sealing\nTailpipe\nExhaust valve not sealing\nOil fill cap / dipstick tube\nWorn piston rings\nBubbles in coolant reservoir\nHead gasket or cracked head\nNeighboring spark plug hole\nHead gasket between cylinders\nCam timing out of spec \u2192 stretched chain, worn guides, jumped timing or VVT fault. These are major repairs; confirm with your instructor before quoting.\nStep 11 \u2014 Repair and verify\nTools: Scan tool, torque wrench.\n\u2022 Make the repair. Torque spark plugs to spec.\n\u2022 Clear codes. Run the engine and watch misfire counters and fuel trims.\n\u2022 Road test under the same conditions shown in the freeze frame.\n\u2022 Confirm the misfire monitor shows complete / passed and no codes return.\nWhat it means: If counters stay at zero and trims are normal, the repair is verified. If the misfire returns, go back to the step where your results were unclear \u2014 there may be more than one cause.\nHard-to-find causes: If every test passes, ask your instructor about carbon buildup on intake valves (common on GDI engines), a clogged EGR passage, a damaged crankshaft reluctor ring, or a driveline vibration that fools the PCM's misfire detection.\nQuick reference: symptom to likely cause\nWhat you see\nMost likely cause\nGo to step\nLean trims at idle, better at 2,500 RPM\nVacuum leak\n5\nLean trims at all speeds, worse under load\nLow fuel pressure or dirty MAF\n7, 8\nRich (negative) trims\nLeaking injector, high fuel pressure, bad sensor\n8\nNormal trims, misfires on several cylinders\nWorn spark plugs\n6\nMisfire follows a swapped coil\nBad ignition coil\n6\nMisfire only when cold, GDI engine\nCarbon on intake valves, or vacuum leak\n1, 5\nStarted right after fill-up\nContaminated fuel\n1, 8\nP0016\u2013P0019 with P0300\nTiming chain stretch or VVT fault\n10\nTwo adjacent cylinders low compression\nHead gasket\n9, 10\nCoolant loss, no visible leak\nHead gasket\n3, 10\nStudent worksheet\nStudent name: ____________________  Vehicle (year/make/model/engine): ____________________\nItem\nYour result\nAll codes found\n\nFreeze frame RPM / load / coolant temp\n\nBank 1 total fuel trim (idle / 2,500 RPM)\n\nBank 2 total fuel trim (idle / 2,500 RPM)\n\nCylinders showing misfire counts\n\nVacuum leak found? Where?\n\nSpark plug condition\n\nFuel pressure (spec / actual)\n\nCompression readings, cyl 1\u20138\n\nRoot cause\n\nRepair performed\n\nVerified by (instructor initials)\n\nReview questions\n1. What does the PCM measure to detect a misfire?\n2. Name the three things every cylinder needs to fire.\n3. Why should you look for a shared cause when misfires are random across cylinders?\n4. Total fuel trim is +18% at idle and +4% at 2,500 RPM. What is the most likely cause, and what test comes next?\n5. You swap the coil from cylinder 2 to cylinder 4 and the misfire moves to cylinder 4. What is bad?\n6. A cylinder reads low on compression but rises after adding oil. What is the problem?\n7. Why must you never open a fuel line on a direct-injection engine?\n8. Why should a car with a flashing check engine light not be driven?\n", "capture_note": "Claude's chat reply, then the Claude Docs document text as copied (tables copy as one cell per line; document links copy as plain text)"}