Brief theory (what the EGR does and failure modes)
- Purpose: EGR (exhaust gas recirculation) returns a controlled amount of exhaust gas into the intake to lower peak combustion temperatures and reduce NOx and detonation.
- On 6G72 variants the EGR is either vacuum‑actuated (older) or solenoid/electronic (later). It consists of a valve/pintle and passages through the intake manifold; a control signal (vacuum or electrical) opens the valve.
- Common faults: carbon deposits seize the pintle or block passages; diaphragm/vacuum line leaks; solenoid or position feedback failure; leaking gasket. Symptoms: rough/unstable idle, hesitation, pinging/knock, elevated NOx codes (P0400–P0409 or manufacturer codes), MIL on.

Ordered procedure (diagnose → repair → verify). Read through once before starting; follow safety notes.
Safety first
- Work on a cool engine, in well‑ventilated area. Wear eye protection and gloves. Disconnect the negative battery terminal when handling electrical connectors. Keep away from open flame (cleaners are flammable).

1) Preliminary diagnosis
- Read engine codes with a scanner. Note any P040x or related EGR codes.
- Visual check: locate EGR valve on the intake manifold near exhaust crossover. Inspect vacuum lines/hoses, electrical connector, and mounting for obvious damage.
- Functional quick test:
- Vacuum type: apply handheld vacuum to the EGR vacuum nipple (engine idling and at specified conditions). If engine stumbles or RPM lowers, valve moves. If not, valve/passage or vacuum source is faulty.
- Electronic: with scanner/bi‑directional control or by energizing solenoid per service manual, check that valve moves or that position feedback changes.
- Check for excessive backpressure or clogged catalytic converter if EGR flow is blocked, but primary focus is valve and passages.

2) Prepare for removal
- Gather tools: basic metric sockets, ratchet, extensions, combination wrenches, screwdrivers, vacuum hand pump, wire brush, brass/nylon brush, picks, carburetor/throttle body cleaner or safe intake carbon cleaner, replacement EGR gasket, replacement valve if faulty, replacement vacuum hoses if cracked.
- Disconnect negative battery terminal (especially for electronic EGR).
- Label and photograph connectors/hoses before removal.

3) Remove EGR valve
- Disconnect vacuum hose or electrical connector.
- Remove mounting bolts and lift off the EGR valve. Expect carbon at the mating face and inside passages.
- Remove the gasket; don’t reuse if damaged or brittle.

4) Inspect and test off the car
- Visually inspect valve pintle and seat: heavy carbon deposits, pitting, or damaged seat indicate replacement.
- For vacuum valves: press diaphragm by hand (if accessible) or apply vacuum from a hand pump; valve should hold vacuum and pintle should move smoothly. If diaphragm leaks or valve does not hold vacuum, replace valve.
- For electronic valves: check solenoid resistance per spec (if available) and energize briefly to see movement; if no movement or burnt smells, replace.

5) Clean valve and passages (if valve salvageable)
- Use small brushes and picks to remove loose carbon from mating face and pintle. Use carb/throttle body cleaner to dissolve carbon; soak small parts if needed.
- Don’t damage the pintle sealing surface — use brass/nylon brushes, not steel picks on mating surfaces.
- Clean the intake manifold EGR passage with brushes and cleaner until flow is clear; remove carbon from crossover and ports. Use compressed air to blow out debris (keep protective shielding and do not blow into sealed sensors).
- Replace the gasket with a new one.

6) Reinstall
- Fit new gasket, position valve, and start bolts by hand. Tighten evenly to manufacturer torque (if you don’t have the book, tighten evenly and snug; do not over‑torque).
- Reconnect vacuum lines or electrical connector. Replace any cracked vacuum hoses.
- Reconnect battery.

7) Functional verification
- Clear codes with scanner.
- Start engine and let reach operating temperature. Observe idle and listen for leaks.
- On vacuum EGR: with engine at the specified operating condition (WOT disabled or as per manual), apply vacuum to check that the engine responds and no leaks occur.
- On electronic EGR: use scanner to command the EGR open/close and watch parameters (EGR duty, position feedback) and for return to normal idle behavior.
- Road test under load; confirm absence of original symptoms and that the MIL stays off. Re-scan for stored codes.

How the repair fixes the fault (concise)
- Cleaning restores flow: carbon blocking passages prevents exhaust gas from entering intake; cleaning re‑establishes proper flow and the valve seat/pintle sealing surface so the valve modulates correctly.
- Replacing a leaking diaphragm or faulty solenoid restores control: vacuum or electrical control that can’t move the pintle allows either too much or too little EGR — replacing restores commanded EGR rates.
- New gasket/eliminating leaks prevents unmetered air or exhaust leaks that cause rough idle and incorrect EGR readings, restoring correct EGR fraction and combustion temperatures → reduces knock/NOx and clears related fault codes.

Quick troubleshooting notes (short)
- Valve refuses to move but vacuum present → stuck by carbon or physically seized; remove and clean/replace.
- Valve moves but engine no change → downstream passages or ports blocked or control not enabling at correct time/condition.
- Vacuum bleeds down → diaphragm leak → replace valve.
- Electrical no response + correct wiring/power → replace solenoid/valve.

That’s the ordered theory + repair sequence.
rteeqp73

JDM Mitsubishi 6G72 Engine Compression Test

Mitsubishi DOHC V6 (6G72) Service Highlights Explanation of the Mitsubishi DOHC V6.

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