34667 Dubai · Ford Focus · Gray

# DIAGNOSTIC PLAN DRAFT — Ford Focus, "سحب ضعيف" (weak acceleration)

## 1) SYMPTOM SUMMARY
Customer reports weak acceleration/pulling power (سحب ضعيف) on a Ford Focus. VIN and mileage were not recorded — get both before starting (VIN is needed for correct TOPIx/ALLDATA specs and Autel VIN-specific data). No comeback flagged. Technician notes already point to the oxygen sensor as the cause and a replacement has been quoted/parted — per shop policy, no part is replaced without a test result that specifically implicates it, so the O2 sensor must be proven guilty before it goes on, not assumed.
**ملخص عربي:** الشكوى سحب ضعيف بدون تسجيل رقم الشاسيه أو الممشى؛ الفني افترض حساس الأكسجين كسبب لكن لازم إثبات ذلك بفحص قبل التركيب.

## 2) LIKELY CAUSES (ranked)
1. **Restricted air intake / dirty air filter** — direct power loss, cheapest to rule out, and an air filter change is already on today's quoted list.
2. **Vacuum/boost leak or intake leak (if turbo/EcoBoost variant)** — causes lean condition and perceived weak pull, free to check visually/with smoke.
3. **Ignition system fault (coil/plugs)** — misfire under load reduces power; common on high-mileage Focus.
4. **Fuel delivery issue (low fuel pressure, clogged filter/injectors)** — power drops under load/acceleration demand.
5. **O2 sensor fault (lazy/slow response or stuck)** — can cause a fuel trim-driven power/economy complaint, but is a *secondary* symptom of a rich/lean condition more often than a root cause — must be confirmed with live data, not assumed.
6. **Clutch slipping (if manual transmission)** — customer complaint list includes clutch replacement quote; slipping clutch presents as "weak pull" without RPM/speed correlation. Cheap to check (RPM flare test).
7. **Transmission/engine mount wear causing driveline loss under load** — less likely for pure power complaint but on the quoted parts list; worth eliminating with a visual/load check since it's already being discussed.
8. **Restricted exhaust (catalytic converter clogging)** — less common but causes strong power loss especially at high RPM; cheap backpressure check available.

**السبب الأرجح:** فلتر هواء متسخ أو تسريب هواء أرخص وأسرع للفحص من حساس الأكسجين؛ يجب استبعادها أولاً.

## 3) TEST SEQUENCE (cheapest first)

1. **Get VIN + mileage, run Autel Auto Scan (full vehicle topology).**
   - Expected: no unrelated codes (transmission, boost, misfire).
   - If fail → note all stored/pending DTCs across all modules (esp. PCM, TCM) and correlate before touching any part.

2. **Visual check: air filter element + intake ducting for damage/collapse.**
   - Expected: clean filter, intact ducting, no debris.
   - If fail → replace air filter (already quoted), road test. If power complaint resolves, stop here. If not → continue.

3. **Visual/physical check: engine & transmission mounts (already on quote list) — look for excess movement, torn rubber, or contact with subframe under load (have assistant load engine in gear/brake).**
   - Expected: minimal movement, no metal-to-metal contact.
   - If fail → note as needed but this affects clunk/vibration more than raw power; do not treat as root cause for power loss unless movement is severe enough to affect driveline alignment.

4. **PCM live data (Autel MaxiSys Ultra S2 — Live Data PIDs) with engine at idle then road test recording: STFT/LTFT (short/long term fuel trim), O2/AFR sensor voltage or ratio (both banks if applicable), MAF g/s, boost pressure (if turbo), RPM vs. vehicle speed vs. throttle position.**
   - Expected: fuel trims within normal range (get spec from TOPIx/ALLDATA for this VIN), O2 sensor switching/responding normally, MAF reading in expected range.
   - If fail (fuel trims out of range, O2 sensor flat-lined or slow-switching) → this is the test that proves the O2 sensor is implicated — proceed to step 5. If fuel trims normal and O2 responds correctly → **O2 sensor is not the cause; do not fit the quoted sensor.** Continue to step 6.

5. **If O2/fuel trim data is abnormal: confirm root cause of the trim shift before condemning the O2 sensor —**
   - Smoke test intake/vacuum lines for leaks (free/cheap).
   - Check MAF sensor reading against known-good range live data.
   - Inspect for exhaust leak upstream of O2 sensor (can cause false lean reading).
   - Expected: leak found and fixed resolves trims, OR trims stay abnormal with no leak found and O2 sensor itself fails a slow-response check on scope/live data graph → **this confirms O2 sensor replacement is justified.**
   - If fail (leak found) → repair leak, clear codes, road test, re-check live data before considering O2 sensor replacement.

6. **Autel Active Test / ignition system check: cylinder contribution / misfire counters in live data during road test; visually inspect coil packs and spark plugs if mileage suggests they're due (get service interval from TOPIx/ALLDATA for this VIN).**
   - Expected: no misfire counts, even cylinder contribution.
   - If fail → identify affected cylinder(s), inspect/replace coil or plug per findings, retest.

7. **Fuel system check: fuel pressure/flow reading (use Autel live data PID for fuel rail pressure if available, or mechanical gauge per TOPIx spec) under load.**
   - Expected: pressure holds spec under acceleration.
   - If fail → inspect fuel filter/pump/injectors as indicated.

8. **If manual transmission: clutch slip test — load engine against brake in gear at moderate RPM, watch for RPM flare without road speed increase.**
   - Expected: RPM tracks road speed, no flare.
   - If fail → clutch slip confirmed, proceed with quoted clutch replacement.

9. **Exhaust backpressure check (only if all above are clear) — measure backpressure or use scan tool O2 pre/post-cat comparison.**
   - Expected: within normal range.
   - If fail → inspect catalytic converter for restriction.

## 4) DATA TO COLLECT
- VIN and current mileage.
- Full Auto Scan report (all modules, all DTCs — stored and pending) — save as DVI/pre-scan report.
- Live data snapshot during road test: STFT/LTFT both banks, O2 sensor voltage/ratio waveform (scope if slow-response suspected), MAF g/s, RPM, TPS%, vehicle speed, boost pressure (if applicable).
- Air filter/intake visual condition (photo).
- Engine/trans mount condition (photo + movement observed under load).
- Misfire/cylinder contribution counters from active test.
- Fuel pressure reading value and TOPIx/ALLDATA spec compared against.
- Clutch flare test result (RPM vs. speed) if manual.
- Exhaust backpressure/pre-post cat O2 comparison value.

## 5) SAFETY
- Standard lift safety when inspecting mounts/exhaust from underneath.
- Fuel pressure test: relieve pressure per Ford procedure before disconnecting fittings; no open flame/sparks near fuel system.
- Road test: two-person protocol (driver + observer) if watching live data during acceleration test.

**السلامة:** اتبع إجراء تنفيس ضغط الوقود قبل الفصل، واستخدم بروتوكول شخصين عند اختبار الطريق مع مراقبة البيانات الحية.

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DRAFT — the technician must verify before any part is ordered. مسودة — القرار النهائي للفني.