What causes high positive short-term fuel trim? (2023)

What causes high positive short term fuel trim?

If the LTFT fuel trim readings are trending up (POSITIVE), it means the fuel feedback control system is compensating for an air/fuel mixture that is becoming progressively leaner over time. The most likely cause would be dirty fuel injectors.

(Video) Short Term and Long Term Fuel Trims Explained
(Ratchets And Wrenches)
What causes positive STFT?

One thing that restricts airflow into the cylinders is a damaged catalytic converter that causes high exhaust back pressure. At idle this can drive fuel trims in opposite directions, producing a positive STFT and negative LTFT.

(Video) Understanding Short Term and Long Term Fuel Trim (a SD Premium video)
(ScannerDanner)
What causes fuel trim to be rich?

Rich. Running rich means that there is too much gas in the air-fuel mixture. This can happen for a variety of reasons, but in a normally functioning system, the ECU will tell it to cut back on the fuel flow to compensate.

(Video) (Toyota Camry) Fuel Trim Diagnosis
(Eli TheOBDTech)
What causes high fuel trim at high rpm?

When you increase engine RPM, three things happen: airflow greatly increases, manifold vacuum drops, and the amount of fuel leaking through the diaphragm becomes much less significant. This would cause total fuel trim numbers to work their way back to normal ranges as the RPM increases.

(Video) Look At Long Term Fuel Trim First
(realfixesrealfast)
Can a vacuum leak cause a rich condition?

A failing evap purge solenoid - as a special case of vacuum leak - is able to cause both rich and lean codes: when stuck open after refueling massive fuel vapors will be sucked into the intake and can trigger a P0172/P0175.

(Video) April 28th - Auto II - Fuel Trim MAF and Vacuum Leaks
(Kip Hicks)
How do I reset my short term fuel trim?

This is done by disconnecting the battery, waiting for 10 minutes or so, and/or turning the ignition key to the starter position to discharge the system.

(Video) How to quickly identify a vacuum leak using fuel trim and water
(ScannerDanner)
What does a positive fuel trim mean?

Positive fuel trim values

If the displayed fuel trim value is a positive number, it means that the ECU is increasing the injector pulse width to add fuel to the air/fuel mixture to enrich the mixture because the input data it is receiving tells it that the mixture is too lean.

(Video) Using Short and Long Term Fuel Trims in Diagnostics
(Hunter Automotive)
How does an exhaust leak affect fuel trims?

As the exhaust valve leak increases, the short-term fuel trims are driven negative enough to force the long-term fuel trims to go negative as well. Remember, even with a small leak, a cylinder can still be ignited. An example of this is an engine that misfires at idle only.

(Video) The Trainer #65: Fuel Trim Explained - What It Is , How It Works, And What It Can Tell You
(Motor Age)
What are 2 things that can cause a lean mixture?

There are five factors that could cause a lean mixture to occur.
  • Fuel System. A malfunctioning fuel system can reduce the amount of fuel coming into the engine, causing a run lean condition. ...
  • Oxygen Sensor. ...
  • Air Mass Flow Sensor. ...
  • Computer Malfunction. ...
  • Air Leaks.

(Video) Fuel trims explained (the easy way)
(DiagnoseDan)
What sensors affect fuel trim?

The oxygen sensors monitor the accuracy of the computer's fuel trim strategy. The oxygen sensor is located in the exhaust and monitors the amount of unburned oxygen in the exhaust. This is an indicator of the fuel mixture integrity.

(Video) How to read short and long term fuel trims
(Good2Boost)

How do I fix my engine running too rich?

How to fix a car running rich
  1. Run full diagnostics to find the exact cause of the problem.
  2. Change the car's air duct flap.
  3. Clean the mass airflow sensor.
  4. Vacuum hoses and lines.
  5. Change faulty spark plugs.
  6. Review the oxygen sensor.
  7. Replace the catalytic converter.
  8. Fix the engine.
Mar 15, 2022

(Video) Secrets of Long Term and Short Term Fuel Trims
(DE Nichols)
How do I fix a system that is too rich?

How to Fix P0172 Engine Code in 2 Minutes [2 DIY Methods / Only $8.77]

What causes high positive short-term fuel trim? (2023)
What should my short term fuel trim be?

Both LTFT and STFT can be positive (more fuel) or negative (less fuel) percentages. LTFT and STFT are added together to produce the total fuel trim, and neither should exceed ± 10% in normal operating conditions. Fuel trims (LTFT, STFT, or LTFT+STFT) exceeding ±10% may indicate a problem in the engine or the sensors.

What are 2 things that can cause a lean mixture?

There are five factors that could cause a lean mixture to occur.
  • Fuel System. A malfunctioning fuel system can reduce the amount of fuel coming into the engine, causing a run lean condition. ...
  • Oxygen Sensor. ...
  • Air Mass Flow Sensor. ...
  • Computer Malfunction. ...
  • Air Leaks.

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