Speedometer question (not a newb one) (I think)

[Clawhammer]

Hey guys,

I have a '90 fastback w/automagic transmission. Well the speedometer has worked intermittently since the day I got it. Probably about 40% of the time I drive it's actually working. Can't really pinpoint what makes it work cause it's so random...sometimes I hit a bump and it goes, others it doesn't. Sometimes while flooring it and the tach get's high it'll work but other times it doesn't. Sometimes I'm just cruizing and it'll (the needle) pop up and work for like 5 minutes or all day. Anyway, really random. I know these cars are notorious for speedometer problems and that this is nothing new, but I replaced the speedometer with one from a DOHC and it still does the same thing. So I got a new transmission speed sensor, no deal. The only thing I can think of is the ECU?? Seems like the signal is getting lost between it and the speedo. I know everything's plugged in for sure, and all the connections look fine, so I'm stumped.

Just wondering if you guys could give me any insight on the problem, I'd really appreciate it.

[Luvs2slide]

I heard that a DOHC cluster won't work with a SOHC car no matter the transmission.

[Clawhammer]

I only took the speedo out of the DOHC cluster and swapped it into mine. The only reason that I know of that the cluster wouldn't work is the tachs are not compatable with the different motors.

[Clawhammer]

Either people don't like me or I just always ask questions that no one has an idea about (any tech. forums; cars, compters, etc.).

[Gilboyto]

Have you checked all your grounds underneath the dash? Could be a loose connection somewhere and when you hit a bump it makes temporary contact. I read somewhere when you do the SR20 swap, that you dont necessarily need to swap the whole cluster in, but you can just do the speedo and assembly for it and it changes it all voltage wise for the speedo.

[projectRDM]

Lot of bad info in here, as usual.

The voltage input is the same no matter what cluster or speedometer you use, so swapping clusters or even transmissions has no bearing on that. The signal is derived from the VSS and goes straight to the cluster first, then to the ECU, so it's not ECU related.

Pull the cluster and check for loose contacts on the back of all the gauges, then clean out the plugs on the cluster and on the subharness behind the dash. From there, check the plug going to the VSS, it'll be run along with the transmission harness and should be near the starter area, unplug and clean both sides of it out, then make sure it's plugged back in tight.