Hey all, just wanted to check some stuff here. I'm picking up a new speedo to replace mine since i fubared my trip odo putting in white face guages. Problem is, mileage doens't match. Solution (in my eyes) is to make a simple driver circuit for the speedo and leave it on till it gets back around to where i need it.
My questions:
1-Is the VSS input 5V TTL? or something else?
2-a simple adjustable pulse generator should be sufficient for this, eh?
3-Any idea which pins on the back of the guage cluster are ground, VSS in, and maybe a power?
4-Any idea whats the fastest speed i can run it at without freaking out the electronics? I need to go forward about 95k miles, so this will take a while. I'm assuming 150mph would be safe since eventually this car will go 150 mph. How about 200? or 250?
5-4000 pulses/mile after a bunch of math gets you to ~ 1hz/mph I don't have my calculations in front of me, but does that seem about right?

thanks...ed

 

I can answer some of those:

2 - I would think so
3 - From top to bottom (on the VSS connector) in this pic: gnd,+12,VSS signal

4 - I would say 255mph, but that's just a guess based on computers' magic number (2^8 counting zero). I'd say it's a reasonable guess, since most speedos max out there or at 300.

I believe that's all correct, but I might be wrong; I wouldn't doubt it at this point since I've been awake since mid-day yesterday, and my whole house smells like exhaust fumes 'cause I left the door to the garage open while I was trying to get my friggin car to run, but nobody knows what the heck is wrong with it and I'm pissed.

Now that I'm all vented...

BTW, you still have that black Camaro or are you driving something else now?

 

Uh, i never had a black camaro. I had a red/gold 85 for a while but that got stolen over a year ago. My current ride is in my sig.
Just guessing, but it seems the picture you gave me is a mechanical speedo. It's definitely different than my 92 anyway.
...ed

derf, forgot to include my sig, anyhow, i'm driving a 92 Z28 vert quasar blue w/ tan top. 305/A4. pretty stock, and hopefully will remain a sleeper.

[This message has been edited by Ed Maher (edited February 26, 2001).]

 

The VSS produces an A/C voltage that varies in voltage and frequency as speed increases.

I think 60Hz is 55 MPH. 255 is the max that the computer will understand.

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hehe. oops. Wrong ed. I didn't even look at the post name just the one at the end. he has a black 89. Like I said, I wasn't in my right state of mind (like when you look all over for your pen only to find it behind your ear).

 

GMtech, are you sure about that? I was under the impression that the speedo and ECM both recieve pulses from the VSS at a rate of ~4000 pulses/miles.
I am relatively sure i am right, as i've seen counter based performance timers that jumper the VSS signal.
...ed