So I have owned my 97 civic lx sedan d16y7 for almost 2 years now. 185k miles at this point. Ever since I bought it, the tach would work 20% of the time, but most of the time it would just jump around or read 2k rpms higher than what it was, or get stuck at the bottom past 8k. Recently my exhaust cracked in half where it was rusted, and I am planning on doing a mini me swap soon, so I decided to get a megan racing header, magnaflow cat, and yonaka catback, which is all EX style exhaust basically. So from what I've been reading, the tach problem is either the icm, cap, or rotor in the dizzy, or the wiring, or the cluster. I was pretty sure it was the cluster. But now, I only have the upstream o2 sensor plugged in to my new headers and have the other hole plugged up until my o2 sensor extensions show up in the mail. After the exhaust install, my tach now works perfectly. Did I mess with the wiring harness just enough to fix it? Or is the new oxygen reading to the ecu causing this system to be reset somehow? I am 99 percent sure o2 sensors have nothing to do with the tachometer, and am real curious what happened. I am glad it's fixed just curious why this could have happened! Thanks

 

The tach problem will probably revisit you.

Here's the connector path of the blue tach wire from the ICM to the Gauge Assembly.

The issue could be the ICM, the blue wire or its connector junctions, the gauge assembly, or the tachometer. The most common causes of the problem are a bad ICM or bad tachometer.