jo88gta

Just installed 3.73 gears in my 88 GTA, it uses a 165 ECM and has a Digital Speedometer. Is there any way I can calibrate the speedometer electronically or via the ECM?

Thanks,

jo88gta

ANYONE? If there's not a electrical way of handling the problem is there a stock gear I can use to get it accurate?

CheezX

The '730 has a intstrument panel divisor bit which I changed when I swapped in a T56. Try looking for something like that in the '165 ecm.

jo88gta

Any chance you could be more specific? Using Winbin I don't see anything that specific.

Thanks.

Jim85IROC

iTrader: (2)

I don't believe the ECM has anything at all to do with the instrument cluster on a GTA. I believe the VSS signal is sent directly to the dash cluster, which has its own logic for displaying speed. Since your ECM also needs a proper VSS signal, your best option is just to change the drive/driven gears that turn the VSS.

jo88gta

It is my understanding that the VSS signal going to the ECM is for the T/C lockup. This function no longer exists since I have a manual T/C switch installed. I was also under the impression that the circuit to the speedo was in parallel with the ECM and that the ECM would not control the speedo at all. If that's all true, I was hoping to find a device that would change that signal to the speedo.

With all that said, where would I find a new gear for the transmission that would be accurate for my 3.73 gears?

Jim85IROC

iTrader: (2)

There is a lot more that the computer uses vehicle speed for than just the TCC lockup. Even my 5 speed car runs like a sack of smashed *******s with the speedo unplugged.

SATURN5

Malibu ran like stink when the speedo cable snapped...

Stalled at stops... all sorts of odd things happen.. BW

jo88gta

The speedo is not unplugged. The VSS still connects directly to the ECM, it's way off at higher speeds because of the 3.73 gears. Now that I program my own chips I'll remove the switch and reconnect the T/C to the ECM.

I have checked with GM and they listed the type of drive and driven gears they have. None quite fit my application. That is why I'm trying to find an electronic way of calibrating the speedo. Keeping in mind the speedo is digital, it seemed possible if I could modify the signal it receives.

Thanks for the input.

CheezX

That bit I mentioned was not defined in the ECU file. I found it by reading the hack. The VSS goes through the ECM first. The ECM then outputs another signal to the speedometer. At least thats what it does on my car (90 Firebird). When I swapped from a T5 to a used T56 all I had to do was change the VSS pulse/mile divisor and the speedometer bit. I've never looked at the 165 stuff so I don't know, but it should have something similar.

I think the VSS is used for IAC steps vs MPH so if its disconnected and you disengage the clutch while moving the engine dies

jo88gta

This would be great news if you you could provide me information on where you made the changes and what you changed it to. Any further information would be way appreciated. That would at least give me a starting point.

jo88gta

In your earlier message you said for me to search for that in my 165 bin. How would I do that?

Kat

iTrader: (4)

There is no feature for the 165 ecm as there is for the 730 ecm for the speedo. The signal fromthe VSS goes to the VSS buffer, then gets spilt into 3 different ways. One for the ECM, one for the cruise control module and one for the speedo. The only way to change the reading of your speedo is to change the speedo gears in the tranny for people with the 165 ecm.

The only time I ever messed with the speedo stuff in the 730 ecm was when I did a t56 swap in a friends 91 Z28. Even from what I am told, it isnt good for small changes, such as rear gear changes. But for big changes say going from a T5/700-R4 (2000 / 4000 ppm) to a T56's VSS (roughly 40,000 ppm )

HTH

Kat

kevm14

I think this is what you are looking for:

http://www.dakotadigital.com/Detail....rtNumber=SGI-5

Also, if your car is like mine, you have a DRAC that sorts the VSS pulses and distributes them to the various locations (ECM, dash, etc) that can also be modified. I have the directions at home (I am at work now). E-mail me if you're interested.

You may not need an aftermarket piece. Or you may choose to go soley aftermarket and leave the stock DRAC alone. Finally, you may need to use both, if you need that large of a pulse speed change.