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2005-Ford-E350/RPMLimitPowerIssue/README.md
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John Loper II 4e52c91c9b feat: Confirmed clogged catalytic converters as cause of RPM limit issue 
Diagnosis: Removing forward O2 sensors immediately restored full power.
Test proved the catalytic converters are severely restricted.

Updated:
- README.md: Added confirmed diagnosis section
- progress.md: Marked diagnosis complete, updated next steps
2026-03-29 18:49:00 -04:00

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RPMLimitPowerIssue - RPM won't exceed 3000, no power under acceleration

Overview

Vehicle has a hard RPM limiter at 3000 RPM. No matter how hard you push the throttle, the engine won't rev past this point and there's no power under acceleration.

Severity: HIGH

This significantly affects drivability - the van can't accelerate normally or maintain highway speeds.

Diagnosis: CONFIRMED 🔍

Clogged catalytic converters - The forward O2 sensors are located in front of the catalysts. When removed, exhaust flow was restored and full power immediately returned.

Work Already Done

  • Spark plugs: Replaced recently
  • TPS (Throttle Position Sensor): Replaced recently
  • Forward O2 sensors removed: ✅ Test confirmed this fixes the issue

Initial Diagnosis

Possible Causes (in order of likelihood)

  1. Fuel Delivery Issues

    • Weak fuel pump
    • Clogged fuel filter
    • Fuel pressure regulator failure
    • Check: Test fuel pressure (should be 35-45 PSI)

  2. Air Intake Problems

    • Dirty MAF sensor
    • Clogged air filter
    • Vacuum leak
    • Throttle body issues
    • Check: Clean MAF, inspect air filter, smoke test for vacuum leaks

  3. Exhaust Restriction

    • Clogged catalytic converter
    • Collapsed exhaust pipe
    • Check: Backpressure test or remove catalytic converter temporarily to test

  4. Ignition System

    • Failing ignition coils
    • Bad ignition control module
    • Check: Swap coils, test coils with multimeter

  5. PCV Valve

    • Stuck closed PCV valve
    • Check: Remove and shake - should rattle

  6. Throttle Body

    • Dirty throttle body
    • Electronic throttle control issue
    • Check: Clean throttle body, inspect throttle position sensor

  7. Engine Computer/ECU Issue

    • Limp mode activated
    • Check: Read diagnostic codes with OBDII scanner

Next Steps

Immediate Actions

  1. Connect OBDII scanner and check for diagnostic trouble codes
  2. Test fuel pressure
  3. Inspect/replace fuel filter
  4. Check/replace air filter
  5. Inspect PCV valve

If No Progress

  1. Smoke test for vacuum leaks
  2. Test MAF sensor
  3. Check exhaust backpressure
  4. Test ignition coils
  5. Check throttle body operation

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