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Discussion Starter · #1 ·
Hi all. I recently put 3:43's in my 1996 Formula firebird. So now the speedometer is off by a little bit. Maybe 5 mph or a little more. What I want to know is, can I just get some kind of new plastic gear that goes in the transmission? On my 1994 Mustang GT, I simply bought a new gear that goes on the end of the speedometer itself. Its a little white 23 tooth gear that I bought from late model restoration supply.

The little gear cured my speedometer inaccuracy problems right up. So is there something like that I can do to my firebird?
 

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Since you didn't state if your car is automatic or 6-speed manual. I will answer for automatic cars. The 4l60E uses a metal straight cut gear for the vss that sends pcm and speedometer it's speed signals.

The speedometer itself is electronic with analog readout. A circuit board and pcm signal controls speed read out.

To correct for different ratio gears in automatic cars, the pcm must be re programed with the new gear ratio.

I believe the 6-speed has the same type of gear and also needs to have pcm re programed, but not 100% sure on that.
 

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I wouldn't use any other method than to recalibrate the PCM.

KW
 

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Discussion Starter · #5 ·
Sorry yeah its an automatic. As for tuning the speedo PCM...

On my Mustang, since its a 94, I have found that you can actually download a lot of different "tools" that you can use to work on the car yourself. Instead of taking it to some guy who will charge you $300 to press two buttons. I'm quite computer savvy, more so than most. Went so school for it.

So is there anything I can download that will let me work on my car that way? Anything at all? Even if there is nothing that will let me reset the speedometer to the right calibration, is there anything else I can download that will let me take control of any other functions?
 

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unfortuantely your car being a '96, tuning software is expensive and of limited supply.

the cheapest solution (if your area doesnt have plug-in emissions testing) is:

- used obd-i ecm (about $100, plugs right in)
- resistor for your knock sensor to match the new ECM
- a cable (about $50)
- tunerpro (free) or tunercat (30 day free trial but i think $20 for a definition file or whatever)

that way you have more software and datalogging options on the cheap in the long run, and it's a bit easier to tune too.

otherwise you're ~$400+ for tuning software plus a cable to work with your original ecm.

only other caveat is that obd-i doesn't have crank sensor based misfire detection, if you even care about that.
 

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Fyi.. I've got a used hypertech that shoudl work for ya, . I got My ecu reprpgrammed for my new heads etc...... But a new tune will cost ya about the same h and you'll get more outta it.
 
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