Can fuel trim (LTFT) be too high or too low? Not using stock injectors

Why are my long term fuel trims high?

Why are the fuel trim numbers high? If LTFT or total fuel trim is greater than plus 10%, the PCM thinks the air/fuel ratio is too lean and it’s adding fuel to bring STFT control to the correct range. This presents three possibilities: Unmeasured air is reaching the combustion chambers.

What should Ltft be at idle?

Long-term fuel trim values

Ideally, long-term fuel trims should be at, or close to 0% when the engine is running at a steady speed. However, while changes to the engine speed will (and must) produce changes in the long-term fuel trim value, this value should return to a point close to 0% when the engine speed steadies.

What causes high short term fuel trims?

Short-term fuel trim happens as a result of changes in the oxygen levels of exhaust gases. An oxygen sensor monitors the flow and generates a signal that is proportional to the oxygen levels in the gases. In a properly functioning system, the ECU will react and immediately make changes as the exhaust gases change.

What causes high negative fuel trims?

But when the engine is in boost mode and positive pressure is provided in the intake, the vacuum leak will allow boost air to escape. This causes the fuel trim numbers to become negative during a boost situation. This happens because the PCM is supplying fuel for the amount of air the MAF sensor measured.

What should fuel trim numbers be?
I think I forgot to mention what are some good numbers for your short and long term futures for the short term fuel trim. Anything. From negative to positive 3%. It's considered okay if in other words

How do I reset my long 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.

Can fuel trim cause misfire?

A rich biased O2 sensor may cause inappropriately negative fuel trim on one bank, resulting in a lean misfire. There could actually be too much fuel going to Bank 1, but -35 percent fuel trim is still considered “in fuel control,” so the engine should be running well. However, uneven fueling on Bank 1 could explain it.

How do you diagnose fuel trims?

The fuel trim value is read by plugging a scan tool into the OBD II diagnostic connector located under the instrument panel (on the drivers side near the steering column). When the key is turned on, the scan tool will initialize and start to communicate with the vehicle’s onboard computer.

Does downstream O2 sensor affect fuel trim?

Input from the downstream O2 sensor(s) is used to detect any problems with the converter(s), and to fine-tune fuel trim. If a fault occurs in an O2 sensor or its internal heater or wiring circuit, the OBD II system should detect the problem, set one or more fault codes and turn on the Check Engine light.

Can a downstream O2 sensor cause a misfire?

The downstream or diagnostic sensors only monitor the exhaust leaving the catalytic converter and will not cause such an issue. Other symptoms of a bad oxygen sensor include a rough idle, a misfire, and/ or hesitation when trying to accelerate.

What should the downstream o2 sensor read?

The Downstream Oxygen Sensor (Oxygen Sensor 2)

Therefore, the downstream oxygen sensor (sensor 2) should produce a steady voltage of approximately 0.45 volts.

Can a downstream o2 sensor cause rough idle?

Yes, your o2 sensor can make your engine idle roughly.

This is because the o2 sensor determines the air to fuel ratio. If the sensor goes bad, this function could be disrupted and cause a rough idle.