Lesson on Lambda Sensors vs Fuel Used

[mattr66usa]

Someone that is misinformed has been telling people that you have to change the AFR in the computer with using Methanol injection but there isn't a clean way to adjust the PW of the injection system for methanol since there isn't an input to the computer that measures the flow of the additional fuel. Once upon a time I designed a system that manipulated the mass air sensor voltage output in proportion to error on an aftermarket wideband to correct the mixture in real time since the car only had narrowband sensors on board. This was great when using nitrous oxide or methanol injection..... But Guess What!!!!! We have wideband O2 sensors on board our cars.

Lambda sensors are INDEPENDENT OF FUEL TYPE. They strictly look at lambda (that can be translated to AFR if you want to, but it isn't super important in the grand scheme of things). Lambda is how much oxygen is left over when air and fuel is being combusted. It doesn't matter what the AFR is if the lambda is happy. Let's ask Chat GPT since that's someone's favorite:

I asked:​

does a lambda sensor care what fuel is being burned?

ChatGPT said:​

Short answer: mostly no—a lambda (oxygen) sensor doesn’t really care what fuel is being burned; it cares about how much oxygen is left in the exhaust.
Here’s the clearer breakdown:

What a lambda sensor actually measures​

• A lambda sensor measures the oxygen content in the exhaust gas.
• From that, the engine computer figures out whether combustion was rich (too much fuel) or lean (too much air).

Does fuel type matter?​

• The sensor itself doesn’t identify the fuel (petrol, ethanol, LPG, etc.).
• It just reports oxygen levels.
• As long as the exhaust chemistry behaves “normally,” the sensor works the same.

Where fuel type does matter​

• Different fuels have different ideal air–fuel ratios:
  • Petrol ≈ 14.7:1
  • Ethanol ≈ 9:1
  • LPG ≈ 15.5:1
• A narrowband lambda sensor always treats “ideal” as lambda = 1, even though the actual ratio changes with fuel.
• The engine control unit (ECU) must be programmed or adapted for the fuel being used.

Sensor limitations​

• Some fuels or additives (like leaded fuel or certain sealants) can damage or contaminate lambda sensors.
• Diesel engines usually work differently and may use lambda sensors mainly for emissions control, not fueling.

Summary​

• Lambda sensor cares about oxygen, not fuel identity

Let's have an intelligent discussion about this, because misinformation is misinformation and it needs to be corrected.

 

[Sleeper.Solutions86]

You might be onto something by speaking his language now. Who knew you were bilingual?

 

[76FoMoCo]

A good read. The tattletale is the knox sensor.

 

[mattr66usa]

A good read. The tattletale is the knox sensor.

You mean when you let the knock sensor add timing over the base maps?

 

[Zpak]

More like, depending on it to retard.

 

[mattr66usa]

More like, depending on it to retard

Go ahead and tell me about that, but that leads into a different topic though. But we are talking about the mixture adjustments for methanol in this thread. So you were running methanol and the knock sensors were still trying to pull timing? That doesn't sound anything like the way I set up methanol tuning since I had a whole topic about letting the knock sensors add the timing for meth injection over the base timing maps with the way I tune. Here is a better explanation: https://shoforum.com/threads/tuning-technical-point-2-borderline-timing-vs-mbt-timing.147788/

 

[mattr66usa]

Another dive into CHAT GPT since that is what you seem to trust over someone that has been tuning cars for 30+ years:

I asked:​

Would methanol and gasoline have the same lambda value in the exhaust with optimal combustion?

ChatGPT said:​

Short answer: yes—if “optimal combustion” means stoichiometric, they will have the same lambda value (λ = 1).
But there’s an important nuance depending on what you mean by “optimal.”

---

Why lambda can be the same​

Lambda (λ) is defined as:

λ = (actual air–fuel ratio) / (stoichiometric air–fuel ratio)

So λ is fuel-independent by design.

• Gasoline stoichiometric AFR ≈ 14.7:1
• Methanol stoichiometric AFR ≈ 6.4:1

Even though those AFRs are very different, both fuels at stoichiometric combustion have λ = 1.
So in the exhaust, a true lambda sensor will report the same value for both when perfectly stoichiometric.

---

Where people get tripped up​

1. “Optimal combustion” doesn’t always mean λ = 1​

• Emissions / catalytic converter efficiency: λ ≈ 1 (both fuels)
• Maximum power:
  • Gasoline: typically λ ≈ 0.88–0.92 (Matt runs E10 tuning at .85 to .82 for better knock resistance)
  • Methanol: typically richer, λ ≈ 0.75–0.85 (Matt already running Lambda here so already good to go)

So if “optimal” means best power, methanol and gasoline will not have the same lambda.

2. Sensor type matters​

• Wideband O₂ sensors report true lambda → directly comparable between fuels
• Narrowband (gasoline-calibrated) O₂ sensors are centered around gasoline stoich → can be misleading with methanol unless interpreted carefully

---

Summary​

• Stoichiometric combustion:
  Methanol and gasoline → same lambda (λ = 1)
• Best-power mixtures:
  Methanol runs richer (lower λ) than gasoline

 

[Zpak]

Matt, I was merely clarifying a statement. The discussion was O2 sensors having one job regardless of what’s being burnt. Downstream of that (well I guess technically upstream, ha!) is knock telling you whether it likes it or not. Not sure why you equate that as a need to defend your personal calibration.

 

[mattr66usa]

Matt, I was merely clarifying a statement. The discussion was O2 sensors having one job regardless of what’s being burnt. Downstream of that (well I guess technically upstream, ha!) is knock telling you whether it likes it or not. Not sure why you equate that as a need to defend your personal calibration.

I wasn't defending, I was just looking for clarification. I'm sorry if it came off that way.

Honestly if methanol didn't have a corrosion issue and water-absorbing issue and fuel flow demand issue, it would be a great performance fuel to run the car on at 100%. I'm just helping people understand the facts about it in these threads and thus dismantling each brick that is a piece in the wall of the lies and misunderstanding that 802SHO is spewing lately. The more people that can see through his BS, the better off the community is because they will be truly educated on the subject matter. I'm not asking for followers, I'm looking for a factual debate about the topics that are part of this platform. So far though, it has been nonfactual accusations without substance from the other side.