Fullauto Posted January 28, 2018 Share Posted January 28, 2018 Finally got the stock tachometer working. Jus wanted to pass along the details. PSI LS3 harness (white wire to tach) stock 1978 280z tach modified by Johns in Dallas. Hooked it up and no tach reading at all on the gauge Stopped by my tuner and the settings are 14 and 15 on the resolution. He thought there should be a good voltage reading. PSI said should have a 5v output Square wave (need oscope meter) I could only read a miniscule reading on the meter .05v and a little frequency wave but almost flat. Decided to try the 1000 ohm resistor attached to a 12v source then spliced into the tach signal wire. As per PSI instructions that came with harness. This bumps up the voltage from the signal wire. Cranked up the car and the tachomter reads perfectly. Amazing how low the voltage from the e38 ecm is!! Hope this helps someone.. Tadd Quote Link to comment Share on other sites More sharing options...
blu240z Posted January 28, 2018 Share Posted January 28, 2018 Had same problem figured it out after sending tach back to John now works great Quote Link to comment Share on other sites More sharing options...
carzan Posted June 7, 2019 Share Posted June 7, 2019 What was the modification done to the tach? Quote Link to comment Share on other sites More sharing options...
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