Mechanical speedo, possible? - Fuel Economy, Hypermiling, EcoModding News and Forum

underitall · 11-26-2009, 08:36 AM

Hi all.
I'v just signed up to the forum, as this place looks great!
I have a 1996 Volvo 440, 1.8i Petrol, which is not OBD compliant, and has a mechanical speedo.
Two things:
Does anyone know where the fuel injectors are exactly located, or the wires I can tap into them are.(I'v looked around, but have no idea whatsoever(I do have access to the ECU though))
And, would it be possible to modify the MPGuino code, to have a push button(That it would read) and I click every time a 10th of a mile goes past, to obtain my instant MPG that way?
Many thanks for any help,
Tom.

dcb · 11-26-2009, 09:58 AM

well, it's a bit hokey, but with no onboard speed signal, you can just connect the speed/vss lead to a small pushbutton perhaps that will flash a 12 volt blip. Then set vsspulsespermile to whatever (20?)

More practical is to just get good at doing the math in your head, divide your MPH by the GPH (Gallons Per Hour) and you have MPG. Use the cars built in trip/odo for larger samples and compare to the fuel used.

Car probably has a speed signal already though, got any schematics?

underitall · 11-26-2009, 11:36 AM

Thx for your reply.
Without trawling trhough alot of stuff, I don't have teh Scematics at the moment.
I had a look over the code, and 1259 lines...I don't understand it, really.
I would like to be able to cut the whole script down, so it's just the basic MPG, no trip meter or any of that.
I am also thinking about making a basic one for the PICaxe.(Any takers?)
Thanks again,
Tom.

dcb · 11-26-2009, 12:21 PM

the trip is what really makes it most useful. Even if you don't have a speed/distance signal, knowing how much fuel it takes you to get to work and trying to use less the next day is the important thing, not an instantaneous reading perhaps when the wind was from the right angle.

But I haven't suggest anything that would require programming changes in this thread.

nickdigger · 11-26-2009, 04:14 PM

There is a possibility that you might have an electric VSS signal. Some older cars (Mazda RX7, Honda Prelude e.g.) have manual speedo cables, but the speedo itself sends out a digital signal from the instrument cluster to the cruise control. Something to look into, if/when you dive into your schematics.

CoastRider · 11-27-2009, 12:27 AM

Quote:

Originally Posted by nickdigger

There is a possibility that you might have an electric VSS signal. Some older cars (Mazda RX7, Honda Prelude e.g.) have manual speedo cables, but the speedo itself sends out a digital signal from the instrument cluster to the cruise control. Something to look into, if/when you dive into your schematics.

It's a 96 and fuel injected It almost has to have a vss.

My truck has a cable driven speedo and a vss sensor.

Do you have abs?

Superturnier · 11-27-2009, 04:56 PM

I just installed my mpguino to my winter car (1994 renault with efi) and I did not find any vss signal generator from it. It has a mechanical speedo.

So I took my old bicycle "computer" which has the magnet and pickup to count the wheel rotations and crawled under my car.
I attached the magnet to the driveshaft with "tie straps or whatever you call them?" and the pickup sensor close to the magnet so that it can sense the magnet.

The sensor has two wires. The other I connected to a fused +12V source and the other wire to the mpguino vss connection.

This setup was quite easy and it gives very accurate readings.