Obdii Vpw

[srspinho]

Hi friend,

I know it´s a bit late for this post, but here we go ...

I was making some experiments with my new Opel Corsa (Brazillian version - small 1.0 litre engine - 79 Hp)

The car is good, but I don´t use gasoline, but Alcohol. The performance is good but the consumption is very high,
specially on heavy duty or high speed.

I did a small "on-board" (with lot of help from this forum) computer for my old Opel Corsa, but without Fuel Consumption display.

Now, i Would like to implement that function.

I Did some search on internet and I foud this :

http://www.eelkevisser.nl/fuel.htm

Don´t worry about the display. This display is just an I2C module made for GM/Opel cars, like Astra, Corsa Meriva etc.

They are monitoring the Car´s speed sensor and the Injector´s "on-time"

My doubt is : do you think the method used by the author really eficient ?

Did you have some progress on implementing the GM VPW ? (i´m still trying with an old GM´s corsa ECU on my desk - but with out success).

Regards

Sérgio

[Acetronics2]

Hi, Sergio

The mesuring method is quite simple and widely used ... it's based on the on-state duration of the injector ... ( your car has a single injector for the 3 (?) cylinders ...)

the more it stays open, the more Alcohol you drink ( or may be your car drinks ??? )

Pression is a constant, so fuel rate is linearly proportionnal to time ... now just have to find mileage info and make the division ...

and convert result into the Opel displaying protocol ... of course.

Alain

[srspinho]

Thanks ALain,

actually, my car can "drink" gasoline, alcohol or both, mixed. The car´s ECU control the correct amount of fuel.

My car has 4 cylinder and 4 injectors (1 injector for each cylinder). Should I measure the "on-state" for each cylinder ?

I´m counting pulses from the speed sensor using Timer 0 (as a 250ms timer) and Timer 1 as a tick counter.

Can I use the CCP module (to measure the on-state time) without my timers stop working ?

When I built my first digital speedometer/hodometer/termometer for my old opel corsa, I had a perfect signal from my speed sensor : When the car was stoped, I have no pulses. When the car start moving, I had 8 pulses / turn.
But now, I don´t know why, when I start my new opel´s engine, the hall sensor start to send me 2 pulses/sec with the car stoped. When I start moving, it gives me to 10 pulses / Sec.

I have built myself a new speed sensor with a hall-effect sensor inside a rigid plastic capsule. This solution gives me 8 pulses/second (8 small magnets were fixed close to the sensor. It was a really hard work...

I´m still thinking on how to fix the problem on my original speed sensor. As I´m making 4 Timer1 readings / second I will have to work arround this problem envolving the "false" pulses.

Anyway...I did really appreciate your reply ! ! !

Regards !

Sérgio

[Acetronics2]

Hi, Sergio

I didn't know the 1.0l 4 cyl ... just 1.2l 3cyl and 1.4l 4 cyl ... apologies, then.

If your engine is in a good condition ... we can consider all injectors give the same amount ... the error will be very very small.

Considering the injection duration, you can measure for the 4 injectors ... just "for the sport".

Using a CCP is a good Idea for measuring ... as you can use the same "timer" to measure the 4 injectors ( they do not bleed at the same moment ...) and interrupts will tell you only when the result is ready to read ( Capture mode )

Alain

[srspinho]

Hi Alain,

Talking about the Fuel Consumption, have you ever had success on using the following formula to do that ?

( Injector_"on"-time / Fixed_time_interval ) * Revolution time * calibration_constant = L/km.

After some long time and some good experiences (and some bad . . .) me and Sylvio (more Sylvio than me), could calculate the fuel consumption using the Darrel´s Instant Interrupts.

We are reading the car´s speed (via timer 0), setting a 500 ms timer and reading the Injector´s in-time via CCP1 (I´m using a 16F877 and Sylvio a 16F88).

We are using the formula above to calculate the consumption, we are assuming that we have 2 injectors firing on each engine´s revolution.

Everything is ok, but Sylvio told me that when he is driving at 130 Km/h, the formula gives something like 30 Km / Liter (he did a modification on the formula to get this) What is really high (amazingly high…), since he is burning alcohol instead of gasoline.

Do you know if measuring just the on-time of one injector and the speed are really enough ?


Thank you !

Sérgio

[srspinho]

Hello friends !

Well, this last weekend, I did install my On-board computer in my Opel Corsa and drove about 250 km in a short trip to the beach.

I was driving in a very good road with a perfect asphalt. But, the road has some small declivity and some small ascent also.

When I´m driving at 90 km/h / 3500 RPM on 5th gear, in a very plain part of the road I can read a consumption of 14 / 15 Km / L (almost constant) - Normal for my small 1.0 L engine.

But, when in the same conditions I get a small declivity, the engine´s load is smaller so, the car´s ECU control the necessary amount of gasoline which is lower even if the speed and the RPM are the same. In this case I can read 20, 25, 30 km/l

In the other way, if I get a small ascent, the gasoline´s consumption gets really high and I can read something like 7 or 8 Km / L at the same conditions, since the engine needs to burn more gasoline to keep the speed.

I don´t know if it is right, but, I think it makes sense.

Regards !

Sérgio

[leisryan]

Guys
Whatabout if the injector is low impedance and using pwm to regulate current or voltage? how can we measure fuel then? do we need to create a fuel lookup table in a particular RPM range?

Yours trully
ryan