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Different fuel and Lambda reading

EFI Tuning Fundamentals

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Hi, I have a question, is the Lambda sensor been calibrated and always read 14.7:1 firmly on pump gas? If so, than when I use E85 fuel which shows on the document attached the Stoichiometric is 9.8:1, so the lambda should read (9.8/14.7)0.66~ 0.67 instead of 1?

This is a common cause of confusion.

The gauge reads the lambda values, and the gauge calibration is responsible for converting that to the "AFR". With petrol/gasoline the stoich' lambda value of 1.0 corresponds to 14.7:1 and that is what the gauge reads.

If you use a different fuel, such as the E85 you cite, at an actual AFR of 9.8:1 the lambda is going to read 1.0, but because the gauge is calibrated for petrol/gasoline the gauge will still read 14.7:1. If you're lucky, you may have an option to change the fuel type in the gauge, but what happens when the pump's "E85" isn't accurate, maybe diluted to E47?

When possible, especially if different fuel blends are being used, it's best to just work with lambda values*, because that is directly relatable to the fueling being rich/lean. Some gauges will give the option of displaying either, and almost all ECU/dash readouts will have the option.

If you don't have that option, just consider 14.7:1 as being in the middle with anything leaner leaner, and anything richer richer. Don't double think about what it's actual AFR is on the E85 - but if you REALLY want to, just make up a simple conversion chart.

*If you're used to just using petroleum fuels, and AFR's, this can be confusing - alcohol based fuels are 'modern' to older chaps, like me.

Merry X-mas !! Thank you for the explanation, much appreciated.

so if I am going to use different fuel, I’ll have to calibrate the Lambda (wide-band O2)setting from the Manufacture ECU tables/gauge to set or convert it to read the specific fuel I am using for an accurate reading and further to approach an accurate fuel adjustment right? otherwise I would be having risk of damaging the engine if I am running lean/leaner or rich/richer than I though.

Uh, yes. The AFR reading will ONLY be accurate for the specific fuel it's calibrated to, and "E" fuels can have quite a large variation in the actual alcohol content - and they're going to be rather different from petrol/gasoline.

You can keep using the gauge on it's petrol/gasoline calibration where lambda 1.0, stoich', is shown as 14.7 and ignoring what the actual is because you don't actually need to know that, just where the fuelling is compared to the lambda value.

As I said, if the gauge has the option of dispalying lambda, which is actually the raw data all gauges convert from, it's much better because it doesn't change with the fuel blend. When you buy E85, for example, there's normally quite a range of tolerance for the fuel, potentially anything from E40 to E90 or even more variation depending on your local legal definitions. If you're using the AFR, or rather a gauge calibrated to the AFR, and you're trying to work from that, it will keep changing.

When you get used to lambda, it's MUCH easier to work with, even if you need to buy a new gauge to do so. It also looks 'trick'.


Did a quick check and found this HPA chart for converting what your petrol/gasoline AFR gauge reading is compared to the lambda, and some other fuel examples. I would remind you that unless you're using race quality, or you have actually confirmed the blend, "E" fuels are nominal.


Great! Thanks for explain to me patiently and even providing useful info, I been thinking about what you said the “E” type of fuel got more range “tolerance”, I assume it’s related during combustion process & result falls on safe side over all of consider damaging the engine compare to patrol/gasoline, therefore using the 14.7:1 AFR calibration on lambda would be fine unless if I plan to go full race and need to be more precisely . got it! Really helpful and clear my mind.

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