1993-1994 Mazda RX7s like previous RXs seem to develop problems unique to their generation e.g. early second Turbo 2s have vibrations in the drivetrain more specifically, imbalances associated with the transmission. Third gens. (93-94) RX7s are plagued with instrument (gauges) problems and speedometer- odometer issues are common. I am working on a automatic 94 rx7 that has a working speedometer but an odometer that recently stopped showing. There are some places here in Florida that claim to be able to bring these units back to life. I made the decision to do some investigations including online threads to tackle the odometer issue. In this particular the engine check light was on and flashed 6 times for speedsensor malfunction. First order was to replace speed sensor (after checking wiring) which sells for $271.0 from the mazda dealer, result; nothing changed. I removed instrument cluster which is quite a job to check speedometer- odometer itself. To my delight, there it was a burnt 1000uf Capacitor just what folks online said I would find, I got the Capacitor online soldered in and also another Cap. of lesser value that’s been known to fail. The grand result was that the odometer worked! but only for a few minutes after starting the car. No codes came up from the computer though, but there must be other problems in the speedometer circuit board and my guess is that the culprit is probably a diode but which one. Ahhhh the saga continues……. I will post anything else that I find provided that I sum up the courage to go back into the 94 RX7’s instrument cluster….what a job!
Did you ever get this resolved? I’ve got a ’93 w this same issue. Every once in a while the odometer will pop on out of the blue, but only for a few min. This only happens a couple times a year… my car seems to have a mind of its own sometimes.
Never did anything else with odometer issue. I would encourage anyone to try the “fix” because it might be just a matter of replacing capacitors.
There are some fixes and pics at RX7club.org.
I have the same problem, along with a check engine light and a hold light, but not brave enough to pull the cluster myself.
Pull the instrument panel, and remove the speedometer printed circuit module. Have an experienced electronics person remove and replace all the electrolytic capacitors on the circuit board; and clean up with ethyl alcohol any and all leaked acid and corrosion.
Check for any bad connections due to the acid leaks.
Occasionally a diode or transistor may have been damaged too. Look for obviously damaged ones that may need replacing.
Do this cleanup even before you have any odometer, tach, speedometer, check engine light problems to prevent the acid leaks from causing damage.