Why does my LTFT1 make wilder, faster changes than STFT1?

How long does it take for long term fuel trim to adjust?

five to 20 seconds

In general, it takes anywhere from five to 20 seconds for LTFT to change, and since it’s stored in memory when the engine is switched off, that same LTFT value is used next time the system goes into closed-loop operation.

What should STFT be at idle?

Ideally, the STFT and LTFT should be within a few percentage points of zero when the engine is idling or being held at a steady RPM. Remember, STFT can bounce around quite a bit as when you suddenly snap open the throttle or decelerate. But LTFT can tell you if the average fuel/mixture is running rich or lean.

What causes high positive short term fuel trim?

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.

What causes high long term fuel trim?

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.

What is a good long term fuel trim reading?

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.

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.

What causes high negative fuel trim at idle?

The MAF sensor overestimates airflow at idle, which causes the negative fuel trim values. It then underestimates airflow at cruising speeds, which accounts for the positive fuel trim values.

What causes high negative fuel trim?

Negative fuel trims mean OVER FUELING not lean. If the feedback from the pre cat O2 sensors is telling the computer that there is too much O2 in the products of combustion then the response from the computer is to increase the time that the injectors stay open. That’s where the +ve sign comes from.

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.

Does downstream oxygen 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.

Will a bad 02 sensor cause a miss?

If an oxygen sensor or mass airflow sensor is failing, it could give incorrect data to your engine’s computer, causing the misfire. When a vacuum line is broken, it can cause a fuel-injected motor to misfire.

What can cause a closed loop fault?

On a two bank vehicle Closed Loop – Fault is when one bank O2 sensor or A/F sensor has a fault. This can be caused by a bad sensor or by one bank being extremely rich or extremely lean. The vehicle will then substitute fuel trim corrections from the “good” bank to the bank it believes has a fault.

What makes a car open loop?

In open loop mode, the engine doesn’t listen to nobody, it just runs off a set of instructions based on where the throttle is at, where the revs are, and so on. The sensor in question is a lambda sensor, also known as an oxygen sensor or air/fuel ratio mixture sensor.

What does OL mean on a scanner?

open loop

OL means open loop,, was the engine warmed up or had been running a few minutes when testing?