ODB-II

[NeoMatrix]

Re: ODB-II

By the way, the correct stoichiometric mixture for a gasoline engine is about 14.7:1....not 1.0

httttps://x-engineer.org/automotive-engineering/internal-combustion-engines/performance/air-fuel-ratio-lambda-engine-performance/

Air-fuel ratio, lambda and engine performance – x-engineer.org

ECU Lambda mapping FAR is known as plus or minus FAR(ideal)...

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We have seen what is and how to calculate the stoichiometric (ideal) air-fuel ratio. In reality, internal combustion engines do not work exactly with ideal AFR, but with values close to it. Therefore we’ll have an ideal and a actual air-fuel AFR. The ratio between the actual air-fuel ratio (AFR_actual) and the ideal/stoichiometric air-fuel ratio (AFR_ideal) is called equivalence air-fuel ratio or lambda (λ).

λ=AFRactualAFRideal(3)

For example, the ideal air-fuel ratio for a gasoline (petrol) engine is 14.7:1. If the actual/real AFR is 13.5, the equivalence factor lambda will be:

λ=13.514.7=0.92

Depending on the value of lambda, the engine is told to work with lean, stoichiometric or rich air-fuel mixture.

Equivalence factor	Air-fuel mixture type	Description
λ < 1.00	Rich	There is not enough air to burn completely the amount of fuel; after combustion there is unburnt fuel in the exhaust gases
λ = 1.00	Stoichiometric (ideal)	The mass of air is exact for a complete combustion of the fuel; after combustion there is no excess oxygen in the exhaust and no unburnt fuel
λ > 1.00	Lean	There is more oxygen than required to burn completely the amount of fuel; after combustion there is excess oxygen in the exhaust gases

Depending on the type of fuel (gasoline or diesel) and the type of injection (direct or indirect), an internal combustion engine can function with lean, stoichiometric or rich air-fuel mixtures.

Image: Ecoboost 3-cylinder direct injection gasoline engine (lambda map)
Credit: Ford

[BillyCarpenter]

Re: ODB-II

You're talking about Lambda. You said stoichiometric as it relates to the perfect fuel/air ratio:


Lambda represents the ratio of the amount of oxygen actually present in a combustion chamber compared to the amount that should have been present in order to obtain "perfect" combustion. ... If a mixture contains too little oxygen for the amount of fuel (a rich mixture), lambda will be less than 1.00.


The 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.

[BillyCarpenter]

Re: ODB-II

Now that we talked about Fuel Trim...how can we use it to troubleshoot an engine?


Lets say that our car is running sluggish out on the highway...it feels like it doesn't have much power. And lets say we suspect the fuel pump is going out.


We can quickly hook up our code reader/scanner and look at Fuel Trim on both banks...assuming this is a V6 or V8 motor. Bank 1 is the left side and Bank 2 is the right side.

Lets say that the fuel trim on Bank 1 is perfect but Fuel Trim on Bank 2 is running very rich. (Computer is compensating for a lack of fuel.)

Could the fuel pump be the problem? No, it's impossible that the fuel pump is the culprit in this case.

Why? Because if it was the fuel pump, Fuel Trim would ALWAYS be off on both Banks.

More than likely it's a Fuel Injector problem on bank 2 that is clogged thus not supplying enough fuel to that single Bank.

Make sense?

[NeoMatrix]

Re: ODB-II

Now that we talked about Fuel Trim...how can we use it to troubleshoot an engine?


Lets say that our car is running
sluggish out on the highway...it feels like it doesn't have much power. And lets say we suspect the fuel pump is going out.


We can quickly hook up our code reader/scanner and look at Fuel Trim on both banks...assuming this is a V6 or V8 motor. Bank 1 is the left side and Bank 2 is the right side.

Lets say that the fuel trim on Bank 1 is perfect but Fuel Trim on Bank 2 is running very rich. (Computer is compensating for a lack of fuel.)

Could the fuel pump be the problem? No, it's impossible that the fuel pump is the culprit in this case.

Why? Because if it was the fuel pump, Fuel Trim would ALWAYS be off on both Banks.

More than likely it's a Fuel Injector problem on bank 2 that is clogged thus not supplying enough fuel to that single Bank.

Make sense?

Where would we find the fuel trim maps in the ECU firmware/bin fi!e?
What would the graph plot look like that would identify the trim data?