Hello I have a 99 Civic Si that has a jdm b18c swap. It has the factory obd2b Si wire harness and has a jumper harness to a obd2a p72-013 ecu. the tachometer (rpm) guage was working perfectly until my Distributor went out. So I replaced it with an aftermarket ebay distributor. the car runs again but no tach? could it be the icm is faulty? I tried to run a jumper wire straight from the distributor blue wire to the back of the tach and still didn't work. but if I unplug the jumper harness and p72 ecu and I plug in the original stock b16a ecu the tach works fine. so I feel like my issue lies in the distributor? just doesn't make sense it would work perfectly, then when I replace the distributor it stops? very odd! crazy electrical problems! 🤕😝

 

Okay so I did a bit of research online and the only thing I could come up with was running a wire directly to the tach wire on the back of the dash cluster. so when I did that I just spliced into the blue wire and did not cut it off from the tach. when I did this the tach still didn't work. so I cut the wire off and now it works. idk why my tach stopped working when I put the new dizzy on but it works now with the jumper wire. stupid electric crap! haha!

 

Not sure but I think on the 99 tach signal from ICM went through the ECU before going to the cluster, I am guessing but if it works with the original ECU installed and no jumper that would be my guess.
I do not have a 99 wiring diagram with me to confirm tach signal routing. 94

 

yes it does go through the ecu. but what I'm confused about is why did the rpm work before with the p72 ecu then when I replaced the dizzy the rpm quit working? makes no sense. so I just jumped a wire straight from the dizzy to the tach. makes me wonder if the new dizzy isnt putting out the correct voltage for the rpm to work through the ecu?