FIXED - Has anyone got the econometer gauge to work with an aftermarket ecu?

[Northern]

Yeah I think it's way easier to have a 2D map in the ECU to use the stock hardware.

Then it's just a matter of making a gauge face to the scale you want.

[Austrianvespaguy]

Funnily enough I've actually been playing with this a LOT recently too. You seem to have figured out a lot so far but here's my full list of findings for comparison:
- Econometer is actually driven, entirely, by the SI board. Traces just come straight from the SI board through the cluster to the gauge.
- SI INPUTS are 12v square pulses from the diff sensor/speedometer for speed and 12v square pulses from the ECU for fuel rate.
- I don't think the circuit is 'active' unless engine is running, though RPM isn't used in the calculation, only speed & fuel pulses.
- ALL you need to do to make it work 'normally' is provide that 12v pulse for fuel rate, with increasing duty cycle indicating more fuel use. TPS, MAP, pulse width, etc. could all be used as input parameters.
- Using the gauge for something ELSE gets trickier, because it's easy to feed something else on the fuel rate input, it'll still get 'skewed' by the vehicle speed. Higher VSS will skew it to the left side and lower VSS to the right, and you can't just hijack the vss input, because then that'll screw up the speedometer. You can clip that input pin from the SI board to isolate it, but I'm still not sure what to easily feed it to make it 'steady.'
- You absolutely can drive the gauge directly using 5v, but it's not actually a stepper motor and so that's tricky too. It's the 4 I think lower pins on the back of the tach that drive the opposite sides of two coils 90deg offset from each other, and the magnetic fields in these coils then align the magnet on the back side of the needle. Think of it as 1 North/South coil and 1 East/West coil. +5v on coil 1 = N, or reversed polarity/-5V = S, and -2.5 coil1 & +2.5 coil2 = SE, etc.
If you can live with just one quadrant it's easier, so I'm working on a small circuit to give one coil a constant voltage, and then use 0-5v to drive the other coil to cover just the 'center' ~10-20 MPG range to indicate AFR. Need to clip those tach pins to isolate the gauge from the cluster circuitry though, and solder your inputs directly to their stubs.
- I might next try jumpering the fuel pulse over to the isolated speed input on the SI board to see what it does with the 'same' signal for both inputs, but I'm not sure if I really expect this to work out not, but stay tuned!

[varg]

Good info here.

I think this is being over-complicated. It's an equation, what you need is a simple board that does what the ECU does natively to drive the econometer. I'd time pulse width and econometer input with an oscilloscope simultaneously, find the factor by which the pulses differ (or log it across a variety of pulse widths and use curve fit to find the equation if it isn't linear for some reason), divide flow rates of stock and current injectors, multiply that by the aforementioned factor, and construct a fairly simple board that that uses this resultant factor to convert injector pulse width to an econometer input. You already know all of the variables except for one: the equation used to convert pulse width to econometer input (which is probably linear). From there it's a 4-wire board that taps into injector output, +12V, gnd, and outputs a an econometer signal. An arduino could do it, there's probably a simpler circuit than that but I'm no EE so I can't just say what it would be off the top of my head.

[Austrianvespaguy]

I think this is being over-complicated.

It's only complicated if you want to try to use the gauge for something OTHER than its intended purpose. If you just want the econometer to work like it did stock and show your current estimated fuel economy, there isn't even a transfer equation involved, it ONLY needs a 12v square wave that matches the injector pulse width. Hell, if you just tied the fuel rate input wire to you injector output, that'd probably even work; I'll double check at work tomorrow whether the stock ECU puts out a going-high or going-low signal to make sure.
The complicated part is that it was designed to work based on two separate input variables, so to have full control over the output you need either to control BOTH variables, or bypass that factory control circuit completely and drive the gauge directly, which then requires 4 inputs/wires to do.

[varg]

In that case intercepting the VSS pin and feeding it a fake conditioned VSS signal is simpler than trying to control the coils in the gauge. As you're probably already aware, the speedometer takes the reed switch input and outputs a square wave that goes to the ECU, econometer, cruise control, etc.

[Austrianvespaguy]

In that case intercepting the VSS pin and feeding it a fake conditioned VSS signal is simpler

Yep I agree this is the best method, and working on the simplest way to accomplish it!

[hozzziii]

OKay this thread went out of my range of understanding wayyyy too fast.
But that's a good thing, it means the people here know what they're talking about, just not me.

But yeah, LOTs of good info here and hopefully we can come to a "guide" of some sorts to turn the econometer to a boost gauge with this knowledge.

So CrazyGhost you're the leading man here, can you try to understand what these gentlemen here have said? And maybe try it out? and let us know your results?

[Austrianvespaguy]

And BOOM! Done!!! All you need to do is bend the vehicle speed signal pin from the SI board out of the way so that it no longer sees the VSS pulse, and then bridge the fuel rate input to the VSS input on the SI board. Now, the SI board will see the SAME pulse for both inputs, and you can drive the whole gauge based on providing this custom 12v pulse via the fuel rate pin. So here goes:

Firstly, the schematic of what we're doing, for reference:


Step 1, bend vss input pin on the SI board back out of the way. Bend rather than cut so the process is reversible. On my SI board it's pin 10 (1 is on the far right if you're looking at the cluster, left in the pic):


Step 2, bridge the fuel rate input pin (9) to the VSS pin (10) on the bottom side of the SI board:


Step 3, Make SURE that the signal you're providing is a 12v square-wave. Use a pull-up resistor (1k~10k ohms) to +12v if you need (my Megasquirt 2 needed this, a 5-volt square wave won't work). Then just connect this to Pin 11 on the white connector (yellow/white wire at the cluster, white/black wire from the ECU connector), and program your duty cycle accordingly! I tested this using the Fidle output from my test MS2 (easy to test this way by adjusting CLT on the stimulator), set to a frequency of 124hz. My results of gauge position (MPG) vs duty cycle are attached, both 'normal' and 'inverted' are included depending which way your signal goes:


Final note, remember that the Econometer gauge will NOT work until there's an RPM signal; aka it won't do anything with key-on-engine-off. Engine needs to be running before it 'comes alive,' even though RPM has no influence on the reading. The final pic for proof!

[hozzziii]

There we go, mystery solved.
Awesome job Austrianvespaguy !

[Panici]

Saving this thread. Interested in making a boost gauge in my cluster.

Does anyone have a gauge overlay image handy designed for boost? I'm not much of a graphic artist :D

[nando]

I don't know if he still makes them, but hoveringuy used to make a board just for this. I've had one for years in my car, and you can adjust it for different size injectors. you just run it inline with the injector signal like stock, and it works perfectly.

[Steve o 77]

soooo old thread I know, but I just wanted to throw this out there for those of you that don't want to have to modify your cluster (yes it's reversible but still). I haven't actually tried this yet but I think an alternative method for canceling out the VSS skew issue would be a 3D table for your PWM output to the fuel rate pin. It would reference VSS and MAP (or lambda if you're going for that). It would definitely require some thought/tuning to get the VSS relationship tuned correctly but I think this could work. I'll come back and update in a couple months when I can actually try this out!