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You can tap wires at the computer. I just put a 12-button navigator in my 84 Turbo Z, from an 87 car. I tapped power and grounds from the radio harness, and the speed sensor and fuel wires from the logic module. It works fine.

Currently I'm trying to figure out how to install the 12-button nav in my 93. The bus is different in the 93, but it has the same speed sensor and fuel gauge inputs, so all I need is the fuel injector signal to be the same range as the older cars. I'll confirm that by using a scope on the Turbo to see what the voltage range is, and whether the 93 has a similar output. Then I have to physically stuff it in the dash. I'm considering under the radio, which involves a little cutting of both the bezel and the flanges of the nav. Will post results.
 

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The ones before that received their info from the logic module, essentially the same thing, same location. That's where I tapped into the signals for my 84 Turbo Z.
 

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Some BCMs are for premium lighting packages, etc. For instance, my 92 had a feature where the headlights turn off one minute after the ignition is turned off, so you don't forget and kill your battery. The 93 has fewer options and doesn't have this feature. It also came without power locks, and some wires at the BCM are not populated.

The biggest challenge will be where to install the navigator. Not quite enough height and depth at the "Daytona" trim strip across the top of the dash. So I'm looking at the bezel, but the bottom slot is narrow and won't be readable from the driver's position, so I'm looking at the slot above it, below the radio.
 

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Make sure you call it the AA body - A body is the Valiant/Dart Duster/Demon.

In my case, I'm putting an older nav in a newer car. The older nav doesn't have the bus communication, so I'm going to see if I can pick up the fuel injector signal from the BCM, and if it's the same as in the older cars. The fuel gauge and speed sensor signals, and power and grounds, and illumination are not an issue.

BTW, the pin connections for an 87 nav are not the same pinout as shown in the 1984 FSM.
 

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Well, that's not optimal.
I put a scope on the fuel injector signal from the logic module to the 12-button EVIC in my 1984 Daytona Turbo Z. Turns out, the signal varies in duty cycle at idle, but is generally 60 ms on, 80 ms off, approximately.

The amplitude is only 0.4 volts. :(



In my 93 Daytona, the data is passed through a serial bus from the body control module. The only place I can pick up the fuel injector signal is at the injector itself (or at the other end of the wire, at the PCM). The amplitude there will be 12 volts, since it switches from a 12V power feed to ground.

So unless I can think of an easy, clever way to scale the pulse down to a 0.4 volt amplitude to feed the EVIC, I won't be able to install it in the '93. Or at least, not have use of the instantaneous mpg reading, and perhaps not the average mpg reading (the latter depends on whether it uses the fuel gauge reading exclusively, or a combination of that and the EFI signal).

Then there's still the problem of how and where to stuff the EVIC into the dash - either in the center stack, or behind the Daytona trim strip across the top of the dash, from center to passenger side.
 

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Neither of these will be available around here. I need the clock function, and want all the 12-button functions.
 

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I'm going to wire up a level shifter that translates the voltage to a level that the EVIC can accept.
 

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I'm talking about the fuel injector signal, not the fuel gauge. The fuel gauge reading was inaccurate, yes - it read 11.2 gallons used, when I topped it off at 10.2 gallons. That was a measure of the change in resistance between fill-ups. You can't compensate for part of the span without calibrating the whole span, gallons full vs resistance reading. And it probably won't be linear. Adding just a resistor will only address part of the span.

But that's only used for the average mpg readings. The instantaneous mpg reading comes from the speed sensor vs the fuel injector signal. The injector signal used in 1984 is only a 0.4V amplitude square wave. The 1993 does not have this signal from the BCM, it's embedded info in the bus signal. So I need to create a 0.4V scaled-down injector signal from the PCM's injector firing. You can't do that with a resistor. It will be a voltage divider feeding the 0.4V signal into an op amp to keep it squared up.
 

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The fuel gauge wire also tells how many gallons used, and it's high by 10% in my car, two tankfuls in a row.

That's not good for me if the EFI pulse also determines the average mpg, if I can't set up that input. Do you know for sure that average mpg is derived this way? I figured I can pull that contact out on my 84 and see what functionality I lose.
 

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John, my distance calculation in the EVIC is accurate, I've checked it against mileage markers and GPS. The fact that both 'fuel used' and 'average mpg' are off by 10% tells me that it's not reading the sending unit accurately.
 

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It's the 84 Turbo Z.

It has a dedicated signal wire from the fuel injector firing, from the logic module. This doesn't exist for 1993; the data is embedded in the serial bus. And yes, there is a vacuum-controlled FPR.
 

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Update on my progress, installing the 1987-88 EVIC in the 1993 Daytona:

I removed the compartment below the radio, carved the plastic trim edges of the EVIC with a Dremel tool to get it to fit in the cavity, and rigged the existing screws to hold it, albeit at an angle. I tapped into the 12V batt, ignition and ground that runs my fire scanner as well as the car radio, and the EVIC does power up and display the correct day, date and time, and elapsed time. It still shows zero mpg instantaneous and average, as well as distance, because I ran out of time/daylight yesterday. I rigged signal wires from the EVIC which I have to splice to the speed sensor and fuel gauge wires at the BCM, a simple task that will take no more than 1/2 hour.

As for the fuel injector signal, as I said before, it is at the logic module in my 1984, but not at the BCM for my 1993 (because the 1993 had a serial bus that carried the injector data). So I'll have to rig a signal off the fuel injector somehow. In the 1984, I was puzzled that when I put a scope on the EFI signal, it showed an amplitude of only 0.4V, which seems impossible. I'm thinking now that I should have unplugged the signal wire from the EVIC and then probed it with a scope, that the EVIC and scope loads together dragged it down. So I'll recheck the 1984 signal and see what I get. Meantime, I expect that when I connect the speed sensor and fuel gauge, I'll get an average mpg reading.

For mechanical mounting, I have scrap plastic strips that I cut out of one of the console compartments, that I'll custom-cut and drill, and glue with epoxy, to make proper mounting tabs so that the EVIC will line up properly in the console stack. This could take about a week, will post pictures when done.
 

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OK, so I was only able to hook up the fuel gauge input last night. Interestingly, I get the following results, mostly understandable without the speed sensor input:

Instaneous mpg: 99.9
Average mpg: 0.0
Fuel consumed: 0.0 (and stayed this way over a 37 mile trip)
Range: started at 322 miles when I first powered the unit, then dropped to 144 miles when I connected the fuel gauge - which was at 1/2 tank). Over a 37 mile trip it dropped to 125 miles.
ETA: 0
Dest: 0
Speed: 0
Trip: Trip completed
E/T: Continuously counted time from when I powered up the EVIC

So I expected that the gas mileage would not read without the speed sensor input. Average 0 mpg makes sense, because it divides 0 miles by gallons used, but 99.9 mpg instantaneous suggests that the reading is based on the fuel consumed, which constantly shows zero - so it's dividing by zero.

It's odd that the fuel consumed will not register without a speed sensor input. Idling should be counted. Must be the way the logic is set up.

On my 84, the speed sensor signal is at the logic module, making it a breeze to connect. On my 93, the BCM does not have a speed sensor pin, only the SBEC (a.k.a., PCM or ECM). So I'm going to grab the signal behind the instrument cluster.
 

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OK, I connected the speed sensor input, and I still do not have instantaneous or average mpg readings. Apparently the fuel injector signal is also required by the logic design of these computers. Interestingly, when I connected the speed sensor, the mpg readings inverted:

Instaneous mpg: 0.0
Average mpg: 99.0

This confirms that a logic state toggled. So I'll have to figure out how to connect the fuel injector signal and scale it.
I do now have the Speed and Trip functions.
 
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