I have install a Firebird dash in my fastback and I am having some issues with the Speedo, when I idle it jumps around 20 to 120+ MPH but when I move it comes back to normal and works great right up until I stop at a light then it goes crazy again.

My question is do I need to make a filter for the Speedo line or Do I have another problem?

The old Speedo worked fine so I am thinking that I have an issue with a missing buffer?

Thanks

Axcessitall
3800 SII SC

This isn't going to be much help but mine did the same thing for a while. After I removed it several times for various reasons, it started working pproperly. I don't know if I had a bad gauge or a bad ground. I do know that my speedo was laying in a puddle of water in the floorboard of the Firebird when I found it and the gas gauge didn't work. I decided to replace the gas gauge and to use the cluster anyway. The last time I removed the clusted and reinstalled it (without making ANY other changes) the speedo started working like it's supposed to. I'd say, check the cluster grounds.

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Roy

double-click on this link to follow my interior build-up https://www.fiero.nl/forum/Forum1/HTML/023174.html

Blue 87 GT w/ 4th generation Firebird interior.
Suncoast Fieros

Judged "Best Custom Interior" at the 20th Anniversary Show @ Pontiac, Mich - 7/2003
Judged "Best Custom Interior" at the 8th Annual Fiero Fun Weekend @ Daytona - 3/2004

ours has not worked since I road tested it with 40 000 ppm instead of 4000 its on my to do list to fix, some day.

I have never had a problem with my speedometer, it is rock solid. But I have the 88 with the 4000 pulse per mile output that I connected to. Its my understanding that only the 88 had this as it was to be used for the electro-hydraulic power steering.

I would suggest picking up an 88 cluster and swapping the electronics board for the speedometer, (this won't affect your odometer if you are worried about the mileage displayed), good luck

- Jonathan

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If you find my advice useful, then please give me a positive rating, thanks...

1988 GT (Firebird Interior),1988 Coupe (Daily Driver), 1985 SE (Project Car), 1985 Coupe (parts car), Firebird Interior Installation Website

If this is for your L67 car, then it should work "out of the box". Like said before, check your grounds.

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My Cardomain page
www.FFDET.com

This is for my L67 with a 5 speed Getrag and yes it is a 4000PPM VSS. The Speedo works great when I drive it is ONLY when I stop that it goes crazy. I am starting to wonder about the way I am tapped into the same line is the VSS to PCM. Maybe at idle my speedo is picking up some kind of noise from the PCM.

If you think about it the PCM wants to see a much higer PPM signal from VSS and then it outputs that to the Speedo but the way I have it the input to the PCM is only 4000PPM and I tap that same input for my Speedo.

Now the test I should do is disconnect the PCM input and see if it still goes crazy at idle because that would tell me if the PCM has anything to do with it.

If it does then I will just run the VSS directly to the Speedo and MIG up a stock Grand Prix VSS at the proper PPM for the PCM.

(My god this post has a alot of VSS, PPM, PCM's and so on's!)

Axcessitall