[oldbeaver]

Hellow AndrzejM,

I have an old diesel myself and tried two ways to estimate fuel yield:

First way:

Compute real time speed (km/hour) and real time fuel consumption (liters/hour) and divide the first by the second, giving me km/l.

This way is noy easy, but is the best.

Getting real time speed: in my case this signal was already available, I just find the correct spot to get it. Check yr car´s manuals.

Computing fuel consumption:

I constructed an arduino device, and second, I installed two tiny electronic flow meters: one on the main fuel conduct (from feeding pump to injector pump) and the second in the fuel return pipe (from injector pump to tank).

Then I read both signals to Arduino and calculated the difference between them. That is the real time fuel consumption.

Of course, it is necessary to build a program to compute all variables and I found that signals are very unstable, so decided to compute a moving average value instead. Every 5 seconds I computed the fuel efficiency using these moving average values.

Second way (easier):

Using the same Arduino board, I constructed a math model (armonic curves) where fuel consumption was a function of only two variables: rpm and throttle position.

(Using this method, you don´t need the fuel meters, which are very difficult to obtain for the tiny fuel flow. Besides, a gentleman from Suiss gave them to me, but they stop working after some months. After that, they broke producing a fuel spill).

At a fixed throttle position, fuel injected by the injection pump depends only on rpm. It is a convex ascending curve, if you know what I mean. I found the curve for my injection pump (a Zexel rotative, probably the same you have) with a pump repare shop and made a family of almost parallel curves where each level represented a throttle position.

This method won´t give you absolute exactitude but will give you very good relative exactitude for comparison purposes. And the model can be adjusted to tank measures, making it very good for estimating real fuel yield of yr car.

If you need more information, please ask.

Best,

OldBeaver