'90 lumina eurosport speedometer/rpm gage

[mdmoffatt]

recently rebuilt my old lumina for son,
transmission had problems for years so replaced with rebuilt
the speedometer and rpm gage not working properly
rpm gage out the top and the speedometer is a slow increase to
maximum found speed pick up on the passenger side of the transaxle
took apart and cleaned did not fix
question: where does the engine get the rpm reference form??
transmission shifting weird, seems to go the overdrive when not necessary the two gages were acting this way prior to the replacement of the transmission
motor totatly rebuilt
any help appreciated matthew

[richtazz]

The engine/tachometer gets it's rpm signal from the crank sensor and ECM. You need to check all your battery cables and grounds for corrosion and or grease, as it sounds like a bad connection. Make sure all the pins in the crank sensor, ECM (electronic control module) and ICM (ignition control module) harnesses are clean and free of corrosion. If all these check out, you may have a bad ECM, as it's a fairly common problem (especially if the GM service number on yours is 1227727).