Normal Long Term Fuel Trims Readings 2006 Chevy Silverado

março 06, 2022 Postar um comentário

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scan tool fuel trim

What Is Fuel Trim?

Fuel Trim is the adjustment the engine computer (PCM) makes to the fuel mixture to maintain a counterbalanced air/fuel ratio. Fuel trim is usually displayed as a Percent reading on a scan tool.

For lowest emissions, the engine computer tries to proceed the fuel mixture balanced around 14.7 to 1 (14.7 parts of air to one part fuel). If the air/fuel ratio is less than 14.seven to i (say 12 to ane), the fuel mixture is RICH. A rich fuel mixture can produce more power (up to a point) but it besides increases fuel consumption and emissions. Conversely, if the fuel mixture is greater than 14.7 to i (say sixteen to 1), it is LEAN. A lean fuel mixture reduces fuel consumption just can also increment emissions if the air/fuel mixture is then lean that it fails to ignite and causes lean misfire.

The engine computer monitors the air/fuel ratio via the oxygen sensor(s) in the exhaust manifold(s). An oxygen sensor is essentially a RICH or LEAN indicator. When the engine is running lean (too much air and non plenty fuel), the O2 sensor generates a low voltage indicate that tells the engine computer more fuel is needed. When the engine is running rich (likewise much fuel and not enough air), the O2 sensor produces a higher voltage point that tells the engine reckoner the engine is getting likewise much fuel and to cut back the fuel commitment. On vehicles that have an Wide Ratio Air/Fuel sensor (WRAF) or A/F sensor, the sensor tells the computer the exact air fuel sensor then the reckoner tin increase or decrease the fuel delivery every bit needed.

Authentic fuel trim values require an accurate feedback signal from the Oxygen sensor, otherwise the engine computer has no mode of knowing whether the fuel mixture is running rich or lean.

When a cold engine is first started, it may take 10 to 30 seconds or more for the heaters inside the oxygen sensors to warms the sensors up to operating temperature. Until that point is reached and the fuel feedback command organisation goes into "closed loop", the fuel mixture is fixed at a predetermined value so no fuel trim adjustments are made. But once the Oxygen sensors are hot and the coolant temperature is high enough for the calculator to go into closed loop, the computer starts to generate fuel trim values and make adjustments in the fuel mixture.

When the engine is close off, the fuel trim values are retained in the calculator'south retentiveness then the side by side time the vehicle is driven it can pick upward where it left off. Erasing the computer'south memory with a scan tool or by disconnecting the battery or the PCM power supply to clear codes too wipes the fuel trim values, which means the reckoner has to first learning the fuel adjustments all over again the next fourth dimension the engine runs.

How to Read Fuel Trim

The fuel trim value is read past plugging a scan tool into the OBD II diagnostic connector located under the instrument panel (on the drivers side about the steering cavalcade). When the key is turned on, the scan tool will initialize and kickoff to communicate with the vehicle's onboard computer. Depending on the tool and the vehicle, it may exist necessary to enter the vehicle yr, make, model and engine VIN lawmaking before the scan tool tin read the data.

The engine must be started and running to read the fuel trim information. Depending on the browse tool and how its carte options are gear up upwardly, y'all choose the pick that allows you to read system live data. This volition display a long list of sensor outputs and other readings called PIDs (Parameter IDs). On this list will be two fuel trim values for inline four and half-dozen cylinder engines, and four fuel trim values for V6 and V8 engines (one pair for each cylinder banking company).

At that place are ii types of fuel trim values shown:

Short Term Fuel Trim (STFT) is what the engine computer is doing to the fuel mixture right now.

This value changes rapidly and tin can bounce effectually quite a chip depending on engine load, speed, temperature and other operating conditions).
Values commonly range from negative 10 pct to positive ten pct, though the readings may leap as much as 25 percentage or more in either direction.

Long Term Fuel Trim (LTFT) is a longer term boilerplate of what the engine computer has been doing to balance the fuel mixture over a predetermined interval of time.
This value is a more accurate indicator of how the fuel mixture is being corrected to recoup for changes in the air/fuel ratio that are occurring within the engine.

STFT B1 is Brusque Term Fuel Trim engine cylinder Depository financial institution i
STFT B2 is Short Term Fuel Trim engine cylinder Banking concern ii
LTFT B1 is Long Term Fuel Trim engine cylinder Bank 1
LTFT B2 is Long Term Fuel Trim engine cylinder Bank ii

What Fuel Trim Values Hateful

POSITIVE fuel trim values hateful the engine computer is calculation fuel (increasing the pulse width or on-time of the fuel injectors) to add more fuel to the engine. In other words, it is attempting to RICHEN the fuel mixture because it thinks the engine'due south air/fuel mixture is running likewise lean.

NEGATIVE (-) fuel trim values mean the engine reckoner is subtracting fuel (decreasing the pulse width or on-time of the fuel injectors) to reduce the corporeality of fuel injected into the engine. This is washed to LEAN out the fuel mixture to recoup for what information technology perceives equally a rich running condition.

Recall, all this is based on what the oxygen sensors are telling the engine computer. If the O2 sensors indicate LEAN, the computer adds fuel and generates a POSITIVE fuel trim value. If the O2 sensors are reading RICH, the figurer compensates by subtracting fuel and generates a NEGATIVE fuel trim value.

By reading the STFT and LTFT fuel trim values on a scan tool while your engine is running, y'all can tell if the air/fuel mixture is running rich (negative fuel trim percentages) or lean (positive fuel trim percentages).

What Fuel Trim Values Should Be

Ideally, the STFT and LTFT should be within a few percent points of nix when the engine is idling or existence held at a steady RPM. Recollect, STFT tin bounce around quite a flake as when you all of a sudden snap open the throttle or decelerate. Simply LTFT can tell y'all if the boilerplate fuel/mixture is running rich or lean.

Skilful LTFT values should be equally shut to aught as possible, though they can range from 5 to eight percent depending on the condition of the engine. If the LTFT is getting up effectually 10 percent or higher, it usually indicates a problem that needs to be diagnosed.

LTFT values that get upward around 20 to 25 per centum volition ordinarily set a P0171 or P0174 lean code.

LTFT values that driblet down to negative 20 to 25 will usually set a P0172 or P0175 rich lawmaking. scantool fuel trim closeup
This scantool is displaying a STFT value of 25 pct. Commonly that would signal a problem,
just in this example the engine is not running (Engine RPM is zero). As soon as the engine starts
and goes into airtight loop, the fuel trim readings will begin to change.

How Fuel, Ignition and Engine Problems Touch on Fuel Trim

Lean fuel mixtures are a more mutual problem than rich fuel mixtures, though either can happen depending on the cause.
LEAN fuel mixtures volition generate college than normal POSITIVE fuel trim readings on your browse tool.
RICH fuel mixtures will generate NEGATIVE fuel trim values.

Possible causes of LEAN fuel mixtures include:

Air or vacuum leaks in the intake manifold, well-nigh the throttle body or at vacuum hose connections.

Weak fuel pump that is not generating enough pressure level or book

Fuel line restrictions (similar a pinches hose or plugged filter)

A weak fuel force per unit area regulator that is non maintaining adequate fuel pressure

Air leaks in the PCV plumbing

Dirty MAF (Mass Airflow) sensor that is under reading airflow into the engine

Dirty or dead fuel injectors

Ignition misfire (a fouled spark plug, weak ignition curlicue or bad plug wire that causes a misfire allows unburned oxygen to pass into the frazzle and fool the O2 sensors)

Compression leaks (bad exhaust valve that allows unburned oxygen into exhaust and fools O2 sensors)

Exhaust manifold crack or gasket leak (allows unburned air into exhaust and fools O2 sensors)

Bad O2 sensor (bespeak shorted to ground and so the sensor reads lean all the time)

Possible causes of RICH fuel mixtures include:

Leaky fuel injector

Excessive fuel pressure due to bad fuel pressure level regulator or restricted fuel return line

Extremely muddy air filter or restrictions in air intake organization

Exhaust restrictions (clogged converter, crushed exhaust pipe or plugged muffler)

Bad O2 sensor (output shorted to voltage then it reads RICH all the time)

Using Fuel Trim to Diagnose Issues

Use Fuel Trim to Diagnose Vacuum and Fuel Commitment Leaks. With the engine idling, look at the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) values. Normal range may be high equally plus or minus viii, but closer to goose egg is best. If the numbers are +10 or college for STFT and LTFT, your engine is running LEAN. Rev the engine to 1500 to 2000 RPM and hold it steady for half a minute or so. If the fuel trim numbers drops back downwardly to a more normal reading, it confirms the engine has a vacuum leak at idle. This is because vacuum leaks have less of a leaning effect on the fuel mixture equally engine speed and load increment.

If the fuel trim readings practice non alter much, the lean fuel status is more probable due to a fuel delivery problem (weak fuel pump, restricted fuel filter, muddied fuel injectors or a leaky fuel pressure regulator) than a vacuum leak.

LTFT fuel trim readings that are trending high might also exist the result of a slight ignition misfire that is not bad enough yet to set up a misfire code but is bad enough to cause a drop in fuel economy. 1 or more fouled spark plugs that are misfiring occasionally, or a weak ignition coil or bad plug wire that is allowing some occasional misfires could exist the cause. For more than data on misfire diagnose, Click Hither.

Y'all can apply fuel trim to identify muddied fuel injectors. 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 condign progressively leaner over time. The well-nigh likely crusade would exist dirty fuel injectors. Fuel commitment can exist restricted past the accumulation of varnish deposits inside the injector nozzles. The set here is to clean the injectors. If the fuel trim values return to normal later on the injectors accept been cleaned, it verifies you have solved the problem. If the fuel trim values don't change after cleaning the injectors, the lean fuel condition may exist due to low fuel pressure level or air/vacuum leaks.

You can use fuel trim readings to check the response of the oxygen sensors and engine computer to changes you make in the fuel mixture. While the engine is idling, temporarily disconnect a vacuum hose. You should see the STFT fuel trim readings spring immediately and go POSITIVE, and the LTFT should commencement to creep up in response to the artificial lean fuel mixture you accept just created by disconnecting the vacuum hose.

To test a rich response, yous can feed some propane vapor from a small propane tank into the throttle body or a vacuum hose connection on the intake manifold. This fourth dimension, you should see a drop in fuel trim readings, with STFT going NEGATIVE, and LTFT creeping downward in response to the rich fuel mixture.

No modify in fuel trim readings when you lot create an bogus lean or rich fuel mixture would tell you lot the engine computer is Not operating in closes loop, or that the oxygen sensor(s) are non responding to changes in the fuel mixture.