So my 95 EJ1 has a wonky speedo. It has for a while now, but it's been getting worse and worse, and nothing I do seems to fix it. It started dropping out (to 0) randomly. Then it went away. Then it came back. Then I replaced the cluster. Then it went away again for a while. Then it came back. Then I replaced the VSS. Then it went away for a day and came back worse. Then I cleaned up every ground in the engine bay, to no avail.

The signal that's getting to the cluster looks like this (please excuse the ishy cellphone pic):



1V per division
5mS per division
Squarewave top is ~4.9VDC p-p (VSS output)
Squarewave bottom is GND
Both connections are at the back of the cluster.

It's not exactly perfect, but it's damn close (spec is 5VDC squarewave). Well above limits for TTL and CMOS logic levels...should be perfectly acceptable.

The only parts left are the wires. None are broken, I checked that already. the connectors are all in good shape. Nothing measures more than a few ohms from end to end, well within specs.

Ideas?

I'm about to throw an output buffer on it to bump it up to a schmitt triggered 5.5V P-P so the cluster will never ever have an issue again.

-dave

 

Anyone?

 

OK, quick update. I've torn the dash apart a few times, and torn apart my spare clusters a few times, and still, nothing sticks out as causing the problem. I did discover that when the system is 'dead' I can bring the speedo back by holding the trip reset button pretty hard. That seems to indicate to me that there is a contact issue somewhere. Unfortunately, 5 nights of tolerance analysis, stackup measurement, and physical pushing and prodding have yielded....nothing. Again.

Any more ideas?