BMW MPG gauge

[Johnsonmjm]

I have a 1994 BMW 325is with a M50TUB25 engine running on Megasquirt 2 v 3.57 with an adapter board made by Goathumper from bimmerforums.

I am trying to figure out how to make the MPG gauge work, but I don't know what signal I can use off the Megasquirt to do so.

When I'm idling and moving it holds past 40 and when I'm not moving it moves back to 0 again. So I know it's getting a signal from the VSS. I just don't know what other wires I have to run to make the d*** thing work. If anyone could help that'd be great.

[tryingbe]

You may want to ask this guy.
http://www.msextra.com/forums/viewtopic ... ge#p449102

[grom_e30]

are you running the stock sized injectors?

[Johnsonmjm]

Yes I am.

[grom_e30]

that should be easier to do then if you are running 2 squirts alternating. i did this on a e30 i connected the fuel rate signal to one of the banks of injectors and it worked.

you can use a 50k resistor and a 5.1v zener to make sure the signal is safe for the obc.

[Johnsonmjm]

Anyway to make a diagram for it

[grom_e30]

https://i.stack.imgur.com/fFeME.jpg

Vin to the injector Vout to the fuel rate signal.

I have not used this directly to the obc my self but, have used this so an arduino could read the injector p/w and output its own scaled p/w signal to correct the obc for running larger injectors so im assuming it should work

[Johnsonmjm]

My question is where do all these signals come from.

[Johnsonmjm]

So use one of the banks of injectors signal and use a 50k resistor inline to pin 46 on my ecu

Why do I need the diode from ground?

[grom_e30]

the resistor and zener will cap the signal that your obc see to 5v.

my e30 obc worked connecting it directly to the injector wiring. but there can be a higher flyback voltage maybe 50v or so, its up to you if you want to take the risk without capping it to a safe voltage.

[Johnsonmjm]

So the wiring would look more or less like this

[grom_e30]

yup

[Johnsonmjm]

Alright I'll give it a try and see what happens

[Johnsonmjm]

yup

So I tried that with the wiring diagram, and it didn't work. But I'm also running 1 squirt per engine cycle with it running on simultaneous.
I tried switching it to alternating and 2 squirts per engine cycle and it started to run like complete s***. So either I'm going to have to completely redo my fuel table, or I'm going to have to leave it on 1 squirt per engine cycle.

Since bank 1 is injecting all the time wouldn't it read a lower in the MPG gauge instead of pegging out at 40?

[rickb794]

Since you say it ran bad after switching squirts,

Is Injector dead time set correctly?

May not be related to your current problem...

[Johnsonmjm]

It is possible.

But I'm not sure where to find the injector dead time values online.
I'm running stock BMW M50tu green top injectors.
I've searched high and low for the dead time values, but I can't seem to find them.

[Laminar]

http://www.msextra.com/forums/viewtopic ... g&start=20

Set an available PWM IO point to a channel proportional to pulsewidth. It doesn't matter if the PW is double or half what it should be, you can characterize the output:

[Johnsonmjm]

I'm on ms2 v3.57 so I don't have that menu option.

[grom_e30]

that menu is for ms3. generic pwm is not a feature of ms2

[Laminar]

Oops, I can see why this is a bit more difficult. You could use a TinyIOx and one of its PWM outputs.