HELP - Does anybody know how to wire up an aftermarket speedometer (I have a VDO programable) so that it sends a signal to the ECM. Stock 1987 Se 2.8 V6 with 5 spd transmission.I am getting code 24 since Rob "Amida" came out and installed dash and gauges. The speedo works fine but the ECM is not getting a signal telling the speed. Thus code 24 plus idle is up because I think computer does not know where to set IAC valve. Is it true that I have to run the original fiero speedometer (circuit board only??) to get the 2000 ppm to the ECM or is there any easier way ?. Any help would sure be appreciated as I'm not to good with this kind of electronic stuff and I cant seem to get a hold of Rob "Amida" lately. Would love to be able to drive my ride this summer.

Thank's Rob


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[This message has been edited by ferrobi (edited 07-13-2010).]

You need to use the OEM circuit board.
You can remove all the old Fiero speedo stuff from it and tap into the 4000ppm signal right here:


Gently scrape the varnish off the trace on the circuit board and solder a wire to it.
I drilled a small hole thru the trace and fed the stripped end of the wire thru from the backside and soldered it, (either side works though, just don't short the wire against another trace)
Run the wire you soldered onto the circuit board to your new speedo input.
Install the circuit board back in the I.P. housing and plug the OEM connector back into it.

VOILA! (orange wire now goes to new speedo)
Your new aftermarket speedo will get a 4000ppm signal and the buffer in the OEM circuit board will send the correct 2000ppm signal to the ECU and the cruise control module.

To take a look at how I did my aftermarket gages go here:
https://www.fiero.nl/forum/F...3/HTML/000111-5.html (starting 3/4 down the page, continued on next page)

[This message has been edited by randye (edited 07-13-2010).]

Thank's a lot I think i can figure it out now - if not i'll post another question

Can you use that tap that supplies a 4k signal to feed a later model ECM that requires one from the VSS?

quote Originally posted by skwrks: Can you use that tap that supplies a 4k signal to feed a later model ECM that requires one from the VSS?

You can, but it would be much easier to simply splice into the VSS signal at the C203 connector, (under the stock ECU)

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painless says the '30 ECM requires a 4k signal in a different wave pattern than the stock TH125 VSS puts out but does not really say how to get it. Fiero addiction made a converter to go the other way but they are not selling anything. This is my sticking point, I need the old signal for the speedo and a new signal for the ECM

quote Originally posted by skwrks: painless says the '30 ECM requires a 4k signal in a different wave pattern than the stock TH125 VSS puts out but does not really say how to get it. Fiero addiction made a converter to go the other way but they are not selling anything. This is my sticking point, I need the old signal for the speedo and a new signal for the ECM

Perhaps they are referring to the later design speed sender installed on the autos around late 80s to early 90s that uses a magneto interupter like the DIS ignition crank position sensor instead of the fiero sender which I believe works like a traditional voltage generator sending a sign wave signal instead of a square wave.