I've been chewing over how to calculate diesel mpg from obd data, as we know diesel engines do not meter fuel out in the same way as a petrol engine, so it makes the calculation very difficult.

But, we can work out mpg when refilling the tank for ourselves.

Would the method below work ? -

Record average speed, along with engine load and rpm, maybe mass air flow too.

Plug in the mpg we worked out when refilling.

Then some how use the recorded speed, engine load, rpm etc to map out the average mpg.

So if you do a lot of town driving

you might get average speeds of 30mph, low rpm values and a mixture of engine loads giving you an average 35 mpg for example

Then if you do a lot of A road driving

Higher speeds of 60mph, higher rpms and more steady engine loads giving you an average of 50mpg

Eventually working out a map of engine speed, rpm and engine load with approximate mpg. The more trips you do, the more accurate the result.

Anyone good at mathmatical formulas?

But, we can work out mpg when refilling the tank for ourselves.

Would the method below work ? -

Record average speed, along with engine load and rpm, maybe mass air flow too.

Plug in the mpg we worked out when refilling.

Then some how use the recorded speed, engine load, rpm etc to map out the average mpg.

So if you do a lot of town driving

you might get average speeds of 30mph, low rpm values and a mixture of engine loads giving you an average 35 mpg for example

Then if you do a lot of A road driving

Higher speeds of 60mph, higher rpms and more steady engine loads giving you an average of 50mpg

Eventually working out a map of engine speed, rpm and engine load with approximate mpg. The more trips you do, the more accurate the result.

Anyone good at mathmatical formulas?

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