Fix P219F: Mechanic’s solutions that WORKED

The P219F: Cylinder 4 Air/Fuel Ratio Imbalance indicates an imbalance in the air/fuel ratio detected in cylinder 4. This means the engine control module has detected that the air-to-fuel mixture in this specific cylinder is not optimal, which can lead to poor engine performance and increased emissions.

P219F quick overview

Meaning	P219F: Cylinder 4 Air/Fuel Ratio Imbalance
Is it serious?	Yes, it can be serious as it may lead to engine performance issues, higher emissions, and possible damage to the catalytic converter.
Possible causes	– Faulty or leaking fuel injectors – Issues with ignition components such as spark plugs or coils – Vacuum leaks in the intake system – Malfunctioning high-pressure fuel pump – Exhaust leaks affecting oxygen sensor readings
How to diagnose?	Inspect Fuel Injectors: Check for leaks or malfunctions. Examine Ignition Components: Ensure spark plugs and coils are in good condition. Conduct Smoke Test: Identify vacuum leaks in the intake system. Check High-Pressure Fuel Pump: Ensure proper operation and pressure. Inspect Exhaust System: Look for leaks that could affect oxygen sensors.

How to fix P219F – learn from mechanics

I looked into P219F service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Honda

Vehicle Information: 2017 Honda CR-V Touring 1.5L

Issue + Repair History:

• MIL light on; rough at startup.
• Fuel factor study showed cylinder 4 lean.
• Long term trim at idle and driving in negative upper teens.

Other OBD2 Codes + Test Results:

• P219f: cylinder #4 fuel mixture deviation

Suggestions to Fix Issue:

• Check valve adjustment first.
• Swap #4 fuel injector with another cylinder.
• Use fuel injector cleaner or ultrasonic cleaning.
• Check for vacuum leak in #4 intake runner.

Final Fix:

• Adjusted valves without resolving the issue.
• Replaced injectors as a set which corrected fuel trims and resolved codes.

Case #2: Toyota

Vehicle Information: 2020 Toyota Camry Hybrid XLE 2.5L

Issue + Repair History:

• Experienced refueling issues 10k miles ago; had vent blown out, now fills fine.
• Popping noise from fuel cap when accelerating, and issues with cap pressure after driving.
• Rough idle for the first minute, then improves.
• Replaced #4 Direct injector, no change in RPM variance.

Computer Codes & Descriptions:

• P219f: engine speed fluctuation #4

Other Test Results:

• Manifold Vacuum Readings: Idle at 19 in., Cruise at 22 in.

Suggestions to Fix Issue:

• Check if purge valve is stuck open.
• Monitor fuel tank pressure to identify issues with the vent valve.
• Consider fuel tank pressure/vacuum caused by bad purge valve or vent valve.
• Inspect if the replacement parts were of low quality or incorrectly installed.

Final Fix:

• After receiving carefully packaged injectors from the dealer, replaced all four injectors.
• Identified that previous damage to injectors occurred prior to installation due to handling.
• Resolved the issue with the installation of new, undamaged injectors.

Case #3: Land Rover

Vehicle Information: 2013 Land Rover Range Rover Evoque Pure 2.0L

Issue + Repair History:

• Vehicle towed in, stalling, starting then dying with black smoke.
• Unplugging MAF sensor allowed the car to start and run perfectly.
• Replacing MAF with genuine sensor didn’t resolve the issue.

Computer Codes & Descriptions:

• P0258: Injection pump fuel metering b low
• P219f: Cylinder 4 air fuel ratio imbalance
• P219a: Bank 1 air fuel ratio imbalance
• P013a: O2 sensor slow response rich to lean bank 1 sensor 2
• P2066: Fuel level sensor b circuit range
• P0133: Heated o2 exhaust gas o2 bank 1 sensor 1 slow response

Suggestions to Fix Issue:

• Check low pressure fuel sensors and high pressure fuel pump.
• Run a high-pressure fuel pump test.
• Inspect for issues like a vacuum plug blowing out of the intake.
• Consider the possibility of a loose intake hose.

Final Fix:

• The problem was due to a blown-off intake hose underneath the vehicle.
• The issue was not initially apparent but was found during a thorough visual inspection.
• The repair involved reattaching and securing the intake hose.

Case #4: Audi

Vehicle Information: 2011 Audi Q5 Premium Plus 3.2L

Issue + Repair History:

• Vehicle exhibited misfires on all cylinders, rich fuel mixture, and poor idle quality.
• Initially had new spark plugs installed and walnut blast service, which did not resolve the issue.
• Fuel-fouled plugs and fuel in oil were discovered.

Computer Codes & Descriptions:

• Po304: Misfire #4 cylinder
• Po303: Misfire #3 cylinder
• P0306: Misfire #6 cylinder
• P0305: Misfire #5 cylinder
• P219f: Cylinder #4 unbalanced
• P21a1: Cylinder #6 unbalanced

Suggestions to Fix Issue:

• Check for vacuum leaks using smoke tester.
• Check timing marks and valves.
• Perform leak down and compression tests.
• Swap fuel injectors between cylinders.
• Check air flow meter, fuel pressure, and injectors.
• Inspect PCV system, vacuum hoses, EVAP purge valve for internal leaks.
• Check fuel system pressure and high-pressure fuel pump.

Final Fix:

• Replaced all six injectors after noticing a rapid drop in fuel pressure post-engine shutoff.
• Changed oil and filter.
• Resolved the issue with no more codes, and the car ran great.

Case #5: BMW

Vehicle Information: 2015 BMW 328i xDrive 2.0L

Issue + Repair History:

• Car had persistent misfires on multiple cylinders and ran rich.
• Initial diagnostics showed no vacuum leaks; misfire codes persisted despite various attempts at repair.
• Replaced ignition coils and conducted fuel system cleaning, but problems persisted.

Computer Codes & Descriptions:

• P0300: Random/Multiple Cylinder Misfire Detected
• P0301: Cylinder 1 Misfire Detected
• P0302: Cylinder 2 Misfire Detected
• P219f: Cylinder 1 Air/Fuel Ratio Imbalance
• P219a: Bank 1 Air/Fuel Ratio Imbalance

Suggestions to Fix Issue:

• Conduct a thorough smoke test for any hidden vacuum leaks.
• Check fuel injectors for proper operation.
• Inspect the high-pressure fuel pump for performance issues.
• Verify integrity of the fuel delivery system.
• Ensure proper installation of ignition components.

Final Fix:

• Discovered malfunctioning high-pressure fuel pump, leading to unbalanced fuel delivery.
• Replaced the high-pressure fuel pump and performed a system reset.
• After repair, the engine ran smoothly with no recurrence of misfire codes.

Takeaway Advice	Description of Diagnostic Step
Check Fuel Injectors	Inspect for leaking or malfunctioning injectors, which can cause fuel imbalance.
Inspect High-Pressure Fuel Pump	Verify the operation of the high-pressure fuel pump, as it can affect fuel delivery.
Conduct Smoke Test	Perform a smoke test to identify any vacuum leaks that might affect air/fuel ratio.
Examine Ignition Components	Ensure that ignition coils and spark plugs are functioning properly, as issues here can cause misfires.
Inspect Intake System	Check for issues in the intake system that could affect cylinder balance.