What should my fuel trims be at idle?
Fuel trim should be checked at idle, at 1,500 rpm and at 2,500 rpm. If long-term fuel trim (LTFT) for bank 1 is 25% at idle, but corrects to 4% at 1,500 and 2,500 rpm, focus on factors that cause a lean condition at idle, such as a vacuum leak.
What percentage should short term fuel trim be idle?
So what should fuel trim values be? Assuming that the engine is in excellent mechanical condition, and that all sensors implicated in metering both intake air and fuel, short-term fuel trim values should generally be between positive 10%, and negative 10% when the engine is running at a steady speed.
What causes negative long term fuel trim at idle?
During idle when the throttle plate is closed, the vacuum in the intake manifold is high and very little air flow is entering the engine, so even a small amount of un-metered air will have an effect on fuel trim. This causes the fuel trim numbers to become negative during a boost situation.
Why is my long term fuel trim so high?
What causes a high long term fuel trim? Here the PCM/ECM is basing fuel delivery on feedback from the engine’s mass airflow (MAF) or manifold absolute pressure (MAP) sensor. Any air leak that occurs AFTER these sensors is a leak that’s allowing UNMETERED air into the engine.
What causes lean condition at idle?
Your engine runs lean if your air-to-fuel mixture is too light – this means that the fuel in your ignition chamber is being igniting with too much air or too little fuel. Your engine running lean is always a symptom of another problem – it could be a dirty MAF sensor, a damaged oxygen sensor, or damaged fuel injectors.
Does clearing codes reset fuel trim?
In many cases, if you graph Bank 1 STFT and B1S1 O2 sensor, you’ll see the oxygen sensor go rich and STFT go lean to adjust the air/fuel ratio. Both STFT and LTFT will normally reset when all trouble codes are cleared.
Can a bad catalytic converter cause negative fuel trim?
The downstream sensors only monitor the health of the catalytics. If the readings between the upstream and downstreams are too close or too far apart a code is thrown for catalyst inefficiency. The only way a catalytic will affect fuel trims is if it’s clogged, but under normal operation it has zero effect.
Can a bad coil pack cause a lean condition?
Actually no, the O2 sensor reads the unconsumed oxygen as lean. A bad coil pack would cause a misfire which would throw a misfire code.
What are the symptoms of an engine running lean?
Running lean, on the other hand, refers to when a car’s engine receives too much air and too little fuel. When this occurs, you may notice symptoms like sluggish acceleration as well as jerking. Some of the most common causes of a lean-running engine include clogged fuel injections, bad fuel pump and a vacuum leak.
What causes a + 13% long term fuel trim?
In this example we’ll examine the possible causes of a +13% long term fuel trim. What the LTFT is telling us is that it has to continuously add 13% more fuel. In other words, the engine is running too lean and the PCM/ECM is forced to compensate by adding more fuel. • Restricted fuel system.
What should bank 1 fuel trim be at idle?
If long-term fuel trim (LTFT) for bank 1 is 25% at idle, but corrects to 4% at 1,500 and 2,500 rpm, focus on factors that cause a lean condition at idle, such as a vacuum leak.
When to check fuel trim in a car?
A useful diagnostic tool is to determine if the fuel trim problem exists in more than one engine operating range. Fuel trim should be checked at idle, at 1,500 rpm and at 2,500 rpm.
What does a negative fuel trim percentage mean?
Negative fuel trim percentages indicate the PCM is attempting to lean out the fuel mixture, to compensate for a perceived rich condition. STFT and LTFT percentages are the adjustments made by the PCM to maintain the 14.7:1 ratio.