What is command equivalence ratio?

OL EQ RATIO = EQ_RAT: Commanded equivalence ratio is used to determine the commanded air/fuel ratio of the engine. For conventional oxygen sensor vehicles, the scan tool should display 1.0 in closed-loop and the PCMcommanded EQ ratio during openloop.

What should fuel trims be at idle?

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 is the ratio of air-fuel mixture?

about 14.7:1The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required.

What is the most efficient mixture ratio of fuel to air stoichiometric ratio?

about 14.7:1The theoretical air–fuel ratio mixture for a gasoline fueled engine, for complete gasoline fuel combustion, the stoichiometric air–fuel ratio is about 14.7:1. In order to completely burn 1 kg of gasoline fuel, the combustion process needs 14.7 kg of air.

What is a normal O2 sensor reading?

A properly functioning oxygen sensor will show a rapidly fluctuating output voltage between approximately 0.1 and 1.0 volts. The time taken for the voltage to change from 0.1 V to 1.0 V (referred to as the lean to rich response time) should be about 300 milliseconds.

What should an O2 sensor read at idle?

A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near minimum (0.1 v) to near maximum (0.9v).

What is the ideal air-fuel ratio for efficient combustion?

around 14.7:1The ideal (theoretical) air fuel ratio, for a complete combustion, is called stoichiometric air fuel ratio. For a gasoline (petrol) engine, the stoichiometric air fuel ratio is around 14.7:1. This means that, in order to burn completely 1 kg of fuel, we need 14.7 kg of air.

How does air-fuel ratio affect engine performance?

An excessively high air–fuel ratio may produce high pumping loss, high peak cylinder pressure, and high compressor outlet temperature. An excessively low air–fuel ratio may produce the problems of deteriorated combustion efficiency, high smoke, and high exhaust gas temperature.

What is a normal long term fuel trim?

Good LTFT values should be as close to zero as possible, though they can range from 5 to 8 percent depending on the condition of the engine. If the LTFT is getting up around 10 percent or higher, it usually indicates a problem that needs to be diagnosed.

What causes high fuel trim at idle?

If the engine uses a mass airflow sensor (MAF), high fuel trims at idle are a classic symptom of a vacuum leak, especially if LTFT decreases at higher engine speeds.

What causes high Ltft at idle?

The LTFT on a cold engine at idle starts at +1.6. As the engine warms to operating temperature the LTFT creeps up to 21.9 at idle. This seems to go up in line with the intake air temperature. On hotter days the LTFT creeps up further to +25 on a hot engine.

What is long term fuel trim bank1?

Long Term Fuel Trim Long-term fuel trim relies on sensors further downstream in the exhaust system, past the catalytic converter. While the sensors’ signal will fluctuate frequently upstream, where short-term fuel trim is measured, the signal at the sensors further down should be fairly constant.

What is the ideal air fuel ratio?

In a perfect world, all gasoline engines would run the ideal air-fuel mixture of 14.7 parts air to 1 part fuel. This target mixture, which is referred to as the stoichiometric air-fuel ratio, is a compromise between optimum fuel economy and optimum power output. A stoichiometric air-fuel ratio causes all of the oxygen and fuel to be consumed inside …

What is the stoichiometric ratio of gasoline?

Although theoretically, the stoichiometric ratio is 14.7:1, the real-world mixture depends on the molecular structure of the gasoline.

What happens when an engine is running rich?

When the engine is running rich, the PCM will reduce fuel delivery, resulting in a negative fuel trim value. On the other hand, when the engine is running lean, the PCM will increase fuel delivery, resulting in a positive fuel trim value. So on your scan tool, you’ll see the short-term fuel trim readings switching back and forth between slightly …

What is fuel trim?

Fuel trim is typically displayed as a percentage on the scan tool. There are two fuel trim data sets: short-term fuel trim (STFT) and long-term fuel trim (LTFT). As you might guess, STFT refers to the mixture adjustments the PCM is currently making, whereas LTFT is an average of the adjustments the PCM has made over a certain period.

How to tell if engine is rich or lean?

The best way to tell whether your engine is running rich or lean is to monitor the fuel trim data via a scan tool that displays live data.

What does it mean when an engine is running too lean?

Generally, the engine is considered to be running too lean when fuel trim is above 10% (with the engine running in closed-loop mode). If fuel trim is below -10%, the engine is typically considered to be running rich. Though on some vehicles, the fuel trim specifications may vary, so it’s a good idea to consult a repair manual or repair database …

What is the PCM in a car?

On modern vehicles, the engine computer, which is often referred to as the powertrain control module (PCM), commands the air-fuel mixture from rich to lean and vice versa. The PCM makes its decisions based on the feedback from various sensors. Oxygen sensors, which measure the air in the exhaust stream, are the primary input to …

How is the amount of air supplied in a gasifier determined?

In a combustor, the amount of air supplied is determined by the stoichiometric (or theoretical) amount of air and its excess air coefficient. In a gasifier, the air supply is only a fraction of the stoichiometric amount. The stoichiometric amount of air may be calculated based on the ultimate analysis of the fuel.

What is the equivalence ratio of plastic?

The equivalence ratio (ER) is perhaps the most important parameters in improving the quality of gas yield in air gasification of plastic [14]. It can be defined as the actual air–fuel ratio (used in the gasification) to the stoichiometric air–fuel ratio for combustion. Its significance was reported by Xiao et al. [15], where it was revealed that ER has more pronounced effects on gas yield and reactor temperature in the gasification of PP than bed height and fluidization velocity. However, it should be noted that the equivalence ratio should not be too high. This is because increasing the ER introduces more air in the gasifier, improves the oxidation reaction with rate more than that of reforming and cracking reactions [16], and eventually enhances formation of more CO 2, H 2 O, and N 2. On the other hand, concentrations of CO and H 2 reduce. However, the reduction in hydrogen concentration with increasing ER may not be high in plastic waste as in the case of biomass. This is because plastic waste has more volatile matter and, accordingly, more tar than biomass. Therefore, cracking and adsorption of the tar at a higher ER maintains a higher operating temperature and leads to more H 2 production [17]. Results by Kim et al. [17] showed that concentrations of CH 4 and heavier hydrocarbons were observed to reduce with increasing ER due to enhanced oxidation reaction. Methane reduced significantly from 15.7% to 3.64% when ER was increased from 0.21 to 0.61. Conversely, reduction in the equivalence ratio enhances evolutions of H 2, CO, CH 4, and other hydrocarbons. This was the case as presented in the gasification of PP by Toledo et al. [18]. It was reported by the authors that while ER was reduced from 0.38 to 0.25, H 2 increased by 33%, CO increased by 70%, and CH 4 increased by 30%, heavier hydrocarbons (C 2 H 2, C 2 H 4, and C 2 H 6) increased by 75%. It should be noted that reducing ER increases tar formation due to a reduction in bed temperature, but the reduction can be compensated for by increasing the freeboard temperature in fluidized bed system.

What is the effect of ER on gasification?

The reduction of high heating value gases like H 2 and CH 4 and heavier hydrocarbons, in addition to the dilution effects of N 2, reduces the heating value of the product gas with increasing ER. Effects of ER on the gasification of mixed plastic comprising PVC, PE, PP, PS, PMMA, and PET in air gasification were also reported by Cho et al. [19]. Their results showed that lower heating value reduced from 13.42 to 7.05 MJ/Nm 3 when the ER was increased from 0.21 to 0.41. A similar result was reported by Xiao et al. [15], with higher heating value reducing from 11.3 to 5.17 MJ/Nm 3 when ER was increased from 0.2 to 0.45 in the air gasification of PP. Although increasing ER reduces H 2 and CO evolution, the overall gas yield increases, and char and tar yield reduce. This is because, with an increase in ER, the bed temperature increases, and a higher amount of gas will be formed in such case during the pyrolysis stage of gasification. The high bed temperature also improves tar cracking, produces light hydrocarbons, and enhances char reactions through the water–gas shift and Boudouard reactions [15]. An increase in the ER from 0.2 to 0.31 in the air gasification of PE by Arena et al. [20] led to a reduction in the tar yield from 14.6 to 7 kg/h. In summary, the equivalence ratio in plastic waste gasification should not be too high to avoid production of syngas with low H 2 and CO concentrations. Also, tar removal may be achieved by other means, like bed additives and thermal cracking.

What is the ER value of a gasifier?

The quality of gas obtained from a gasifier strongly depends on the ER value, which must be significantly below 1.0 to ensure that the fuel is gasified rather than combusted. However, an excessively low ER value (<0.2) results in several problems, including incomplete gasification, excessive char formation, and a low heating value of the product gas. On the other hand, too high an ER (>0.4) results in excessive formation of products of complete combustion, such as CO 2 and H 2 O, at the expense of desirable products, such as CO and H 2. This causes a decrease in the heating value of the gas. In practical gasification systems, the ER value is normally maintained within the range of 0.20 to 0.30. Figure 6.20 shows the variation in carbon conversion efficiency of a circulating fluidized-bed gasifier for wood dust against the equivalence ratio. The efficiency increases with ER and then it starts declining. The optimum value here is 0.26, but it may change depending on many factors.

What is the ER in combustion?

Equivalence ratio (ER) is defined as the air to biomass weight, in relation to the stoichiometric air to biomass weight needed for complete combustion [97].

What is the S/B of biomass gasification?

Steam-to-biomass ratio (S/B) is a key parameter in gasification on account of its influence on the syngas yield and heat content ( Huber et al., 2006 ). Increasing S/B results in more H 2 yield and, therefore, syngas with higher heat content. It also produces lower amounts of tar, due to water–gas shift, reforming, and cracking reactions. However, there exists a limit beyond which any increase in S/B produces excess steam in the syngas. Energy contained in the excess steam along with the enthalpy losses in generating this steam results in low process efficiency. Such issues demand an optimal S/B during biomass gasification.

What is the role of ER in biomass?

The ER represents the actual air-to-biomass ratio with respect to stoichiometry and plays a key role in biomass gasification. H 2 and CO fractions in the syngas are enhanced when ER values are decreased ( De Lasa et al., 2011 ). Higher ER results in lower H 2 and CO yields, with an increase in CO 2, which in turn decreases the heat content of the syngas. It is because of the enhancement in the oxidation reactions. On the contrary, higher ER improves tar cracking due to higher O 2 availability for volatile species to react with as well as due to higher temperature. ER is also impacted by the presence of moisture and volatiles in the feedstock material. Water content up to 15% results in an increase in ER and gas amount, but above 15% causes irregular temperature variations. High-volatile fractions in the biomass feedstock produce higher tar yields.

When was fuel trim standardized?

Global OBD-II fuel trim reporting was standardized for all manufacturers in 2005 and later models equipped with a CAN bus control system.

Why does low fuel delivery cause LTFT?

Low fuel delivery will cause an increase in LT FT as the PCM tries to compensate for extra oxygen in the exhaust stream. Remember, the PCM doesn’t measure fuel flow; it only knows injector pulse width and assumes fuel delivery is correct as commanded. Is equivalence ratio changing, too? If you add propane and see LTFT and equivalence ratio numbers come down, there probably is a fuel delivery problem. If there’s no change, an oxygen sensor may be faulty or shorted to ground. Don’t forget to check this at different speeds and loads, because fuel flow problems often don’t show up at idle.

What is fuel trim?

Volkswagen calls fuel trim “oxygen sensor adaptation,” and Ford classifies fuel trim as a “continuous monitor” that runs when the fuel control system is in closed loop operation. This shows us that fuel trim is an ongoing calculation based on data reported by the oxygen sensor. Extra oxygen in the exhaust indicates a lean air/fuel mixture, so the PCM increases injector pulse width to add more fuel (positive fuel trim). Too little oxygen in the exhaust indicates a rich mixture, causing the PCM to reduce injector pulse width (negative fuel trim).

What causes fuel trim to be affected?

Fuel trim can be affected by just about anything between the air filter and the muffler, including sensors, injectors, ignition, EGR, the engine’s mechanical condition and even the crankcase ventilation system. Fuel trim numbers alone won’t provide a complete diagnosis, but if you know what to look for, those numbers can lead you in …

Is LTFT a coarse adjustment?

Some people think of LTFT as a coarse adjustment and ST FT as fine adjustment. A more technical definition would be additive and multiplicative. Additive fuel trim calculations (STFT) won’t change much with engine speed or load. For example, a vacuum leak would produce an additive calculation because the effects of that leak increase very little with increasing engine speed. Multiplicative fuel trim calculations (LTFT) are greater as engine speed or load increases because, for example, the effect of a partially clogged injector increases as speed and load increase.

Does vacuum leak affect fuel ratio?

Since the amount of air flowing through the vacuum leak doesn’t increase, the leak has less affect on air/fuel ratio at higher speeds and loads, so LTFT will come down as engine speed goes up. When you look for vacuum leaks, don’t forget the various “calibrated vacuum leaks” like crankcase ventilation, the evaporative emissions (EVAP) purge valve and, if equipped, air-shrouded injectors.

What does a very high AFR reading mean?

A very high or very low reading could indicate that the intake AFR is not correct, but getting an actual number would be difficult. Share.

Is oxygen sensor the right choice?

Depending on what you are trying to achieve, the oxygen sensor may not be the right choice, regardless of reading.

All Answers (3)

If mole % known, Stoich O2 of mix per mole mix= {Mole % of Fuel 1* stoich O2 in mole for Fuel 1/mole Fuel1+ Mole % of Fuel 2* stoich O2 in mole for Fuel 12 /mole Fuel2+….}/100.

Similar questions and discussions

Any help on how to determine the equivalence ratio from mixture fractions?

What rpm should fuel trim be checked at?

Fuel trim should be checked at idle, at 1500 rpm and at 2500 rpm. For example, if LTFT B1 is 25% at idle but corrects to 4% at both 1500 and 2500 rpm, your diagnosis should focus on factors that can cause a lean condition at idle, such as a vacuum leak.

How to calculate manifold vacuum?

Don’t confuse the MAP sensor parameter with intake manifold vacuum; they’re not the same. A simple formula to use is: barometric pressure (BARO) / MAP = intake manifold vacuum. For example, BARO 27. 5 in. /Hg / MAP 10.5 = intake manifold vacuum of 17.0 in./Hg. Some vehicles are equipped with only a MAF sensor, some have only a MAP sensor and some are equipped with both sensors.

How to read EGR error?

The reading is based on a simple formula: (Actual EGR Position − Commanded EGR) ÷ Commanded EGR = EGR Error. For example, if the EGR valve is commanded open 10% and the EGR valve moves only 5% (5% − 10%) ÷ 10% = −50% error. If the scan tool displays EGR Error at 99.2% and the EGR is commanded OFF, this indicates that the PCM is receiving information that the EGR valve position is greater than 0%. This may be due to an EGR valve that is stuck partially open or a malfunctioning EGR position sensor.

How much does an OBD II scan cost?

I’ve found that approximately 80% of the driveability problems I diagnose can be narrowed down or solved using nothing more than OBD II generic parameters. And all of that information is available on an OBD II generic scan tool that can be purchased for under $300.

What is fuel trim on a computer?

Fuel trim is a key diagnostic parameter and your window into what the computer is doing to control fuel delivery and how the adaptive strategy is operating. STFT and LTFT are expressed as a percentage, with the ideal range being within /5%. Positive fuel trim percentages indicate that the powertrain control module (PCM) is attempting to enrichen the fuel mixture to compensate for a perceived lean condition. Negative fuel trim percentages indicate that the PCM is attempting to enlean the fuel mixture to compensate for a perceived rich condition. STFT will normally sweep rapidly between enrichment and enleanment, while LTFT will remain more stable. If STFT or LTFT exceeds /10%, this should alert you to a potential problem.

How to check oxygen sensor?

If this method does not work, use a bottle of propane to manually richen the fuel mixture to check the oxygen sensor’s maximum output. To check the low oxygen sensor range, simply create a lean condition and check the voltage. Checking oxygen sensor speed is where a graphing scan tool helps. Fig. 3 on page 57 and Fig. 4 on page 58 show examples of oxygen sensor data graphed, along with STFT, LTFT and rpm, taken from two different graphing scan tools.

What temperature should engine coolant be?

Engine Coolant Temperature (ECT) should reach operating temperature, preferably 190/F or higher. If the ECT is too low, the PCM may richen the fuel mixture to compensate for a (perceived) cold engine condition.

What rpm should fuel trim be checked at?

Fuel trim should be checked at idle, at 1500 rpm and at 2500 rpm. For example, if LTFT B1 is 25% at idle but corrects to 4% at both 1500 and 2500 rpm, your diagnosis should focus on factors that can cause a lean condition at idle, such as a vacuum leak.

What temperature should IAT be?

In the case of a cold engine check-Key On Engine Off (KOEO)-the ECT and IAT should be within 5°F of each other.

How to read EGR error?

The reading is based on a simple formula: (Actual ECiR Position – Commanded EGR) ÷ Commanded EGR = EGR Error. For example, if the EGR valve is commanded open 10% and the EGR valve moves only 5% (5% – 10%) ÷ 10% = -50% error. If the scan tool displays EGR Error at 99.2% and the EGR is commanded OFF, this indicates that the PCM is receiving information that the EGR valve position is greater than 0%. This may be due to an EGR valve that is stuck partially open or a malfunctioning EGR position sensor.

How much does an OBD II scan cost?

I’ve found that approximately 80% of the driveability problems I diagnose can be narrowed down or solved using nothing more than OBD II generic parameters. And all of that information is available on an OBD II generic scan tool that can be purchased for under $300.

What is fuel trim?

Fuel trim is a key diagnostic parameter and your window into what the computer is doing to control fuel delivery and how the adaptive strategy is operating. STFT and LTFT are expressed as a percentage, with the ideal range being within ±5%. Positive fuel trim percentages indicate that the powertrain control module (PCM) is attempting to enrichen the fuel mixture to compensate for a perceived lean condition. Negative fuel trim percentages indicate that the PCM is attempting to enlean the fuel mixture to compensate for a perceived rich condition. STFT will normally sweep rapidly between enrichment and enleanment, while LTFT will remain more stable. If STFT or LTFT exceeds ±10%, this should alert you to a potential problem.

How to check oxygen sensor?

If this method does not work, use a bottle of propane to manually richen the fuel mixture to check the oxygen sensor’s maximum output. To check the low oxygen sensor range, simply create a lean condition and check the voltage. Checking oxygen sensor speed is where a graphing scan tool helps. Fig. 3 on page 57 and Fig. 4 on page 58 show examples of oxygen sensor data graphed, along with STFT, LTFT and rpm, taken from two different graphing scan tools.

What is a MAF sensor?

The Mass Airflow (MAF) Sensor, if the system includes one, measures the amount of air flowing into the engine. The PCM uses this information to calculate the amount of fuel that should be delivered, to achieve the desired air/fuel mixture. The MAF sensor should he checked for accuracy in various rpm ranges, including wide-open throttle (WOT), and compared with the manufacturer’s recommendations. Mark Warren’s Dec. 2003 Driveahility Corner column covered volumetric efficiency, which should help you with MAF diagnostics. A copy of that article is available at, and an updated volumetric efficiency chart is available at