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Speedo not working |
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tweeder 
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Joined: 05 August 2012 Location: Canada Status: Offline Points: 27 |
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 Topic: Speedo not workingPosted: 06 August 2012 at 10:18pm |
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I looked into the speedo and vss but am still confused as to where to start? A previous owner did. 3800 swap with a 866 4l80 CFD 910 hydra-matic(not sure what that is or where it's from). My tac works but no speedo or odo. |
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86 GT Convertable 3800
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bcampbell
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Joined: 14 November 2011 Location: Canada Status: Offline Points: 160 |
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Posted: 10 August 2012 at 11:27am |
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If you could hook up a datalogger you could find out if the
PCM is seeing the VSS signal and go from there. Did the speedometer work at all since the swap or is this recent? If the PCM is getting the VSS signal then you could try using the PCM speedo output wire and make a conversion circuit to your speedo. Like this: http://www.gmtuners.com/fiero/speedo2.gif |
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'86 2m6 F23 5-speed, LSD, 3.5L LX9
'89 Firebird 3500T, T56 |
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CFoss
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Joined: 13 February 2007 Location: Canada Status: Offline Points: 580 |
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Posted: 10 August 2012 at 4:24pm |
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What ecm/pcm are you running?
The regular Fiero vss puts out about 60hz at 60mph or something like that. If it's the original you could put a voltmeter on it which is capable of hz and check it as you drive to see if it's outputting. A scanner is by far the prefered method though. FYI, the original speedo has a 'buffer amplifier' circuit inside it. It would take the vss signal, and then backfeed a signal to the ecm if I remember correctly. When I went to a 1227730 I moved the vss signal directly into the ecm, and then the ecm outputted a signal which supplies the speedo; I used the info in the link bcampbell has referenced above and it works pretty well. Chay |
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86 SE 3.4
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tweeder
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Joined: 05 August 2012 Location: Canada Status: Offline Points: 27 |
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Posted: 10 August 2012 at 11:11pm |
The previous owner said that the speedo hasn't worked since he had it, the owner before him had don the engine swap. |
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86 GT Convertable 3800
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tweeder
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Joined: 05 August 2012 Location: Canada Status: Offline Points: 27 |
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Posted: 10 August 2012 at 11:13pm |
It has te ECM from the engine swap(90 Buick Electra). |
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86 GT Convertable 3800
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Capt Fiero
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Founding Member Joined: 12 February 2007 Location: Canada Status: Offline Points: 4039 |
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Posted: 11 August 2012 at 9:10pm |
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What you need to find out is if the VSS in the trans is even capable of outputting the correct signal for the Fiero speedo. In my case, I simply put a T in my VSS signal wire, ran 2 wires directly to the speedo and 2 wires directly into the ECM. Everything works perfect. For whatever reason, my 93 Caddy ECM reads the Fiero VSS perfect, but the output signal from the ECM was wrong. I am not a signal genius but that is how I got my speedo working.
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Capt Fiero
88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd. |
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tweeder
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Joined: 05 August 2012 Location: Canada Status: Offline Points: 27 |
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Posted: 11 August 2012 at 9:15pm |
I've been told that my tranny is a thm125c not sure if it's compatible? |
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86 GT Convertable 3800
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Capt Fiero
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Founding Member Joined: 12 February 2007 Location: Canada Status: Offline Points: 4039 |
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Posted: 12 August 2012 at 5:08pm |
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The 125C 3spd Auto and was factory on all Automatic Fiero's. So if you inded have a 125C then it will be correct for the speedo. Have you pulled the VSS and checked the gear? If you pull the VSS grab a cordless drill and use that to spin the VSS then check the speedo in the car to see if it moves.
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Capt Fiero
88 Fiero GT 5spd V6 Eight Fifty Seven GT V8 5spd. |
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bcampbell wrote: