Hello, the Long Term and Short-Term fuel trim is how much the engine computer is compensating and adjusting the air/fuel mixture. Ignore the graph, just monitor the numbers, so you're max Long Term is -4.7%. Which is very normal. When the numbers get to be +/-5% or more, then it's time to look into other engine data to determine what might be happening. Right now, the engine computer is reducing the fuel amount by 4.7%. Negative numbers are taking away fuel and positive is adding fuel. I will post some additional information to help. But you have nothing to worry about right now.
The engine computer (ECM) would add fuel (there would be a positive number, ie +10% for example) if there was a vacuum leak somewhere and unmetered air was entering the engine through the vacuum leak. Such as a leaking intake manifold gasket. The Lambda reading is a calculated number, being as close to 1.000 as possible is perfect for what that particular ECM is programmed to do. The Long-Term trim is more of a learned fuel strategy over time, whereas the Short Term is what is happening right now, so that number will change faster while driving.
Looking through the wiring diagrams for this vehicle it looks like Toyota has gone with duel fuel injectors on this year. The main fuel injectors are direct injection into the cylinders and are a very high-pressure fuel system. Usually 800 up to 2000psi, they added the conventional fuel injectors as well into the intake manifold to help clean the intake valves. So, the ECM is taking away a very small amount of fuel for some reason, but it is to keep the emissions within the Federal Standards. I hope this helped some, if you have any other questions just ask. Have a nice evening.
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Monday, April 17th, 2023 AT 5:59 PM
