I am having an issue that when I press the throttle past about 80 percent(ish),1.9 volts or so on a logger, the tach drops off almost to zero although the car is still revving up. There was some car hesitation(I thought) but it does not seem so while in the shop, while logging. It seems to read fine up to 7K and beyond, unless I press the throttle in all the way, if I do that, it drops off at 4500 or less, and goes basically to zero.

Any suggestions as to where to start looking? This engine and wiring was just removed and reinstalled, but it worked fine for about two weeks, including being tuned on a dyno.

I will include a ecmlink log for those who want.

Thanks in advance for any advice!

Is it a 90 ECU?

I have a feeling it's not i had the same issue.when I put the 91+ ecu in my car. At a certain rpm, or past a certain percentage of throttle.the tach went dead on my old car until I put back the 1990 ecu.the 1990 really are a bastard child.but they make a chip you can install internally in the ecu or external version. I believe its on dsmchips.com

Wow, you called it, I swapped in a second ECU I have, and did not think of it! Thanks, been pulling my hair out! I did know that the 1990 tach is different, I just assumed it was the dash that was different, not the ECU - in regard to the tach, anyways.

I unfortunatly had the same problem on my 90 eclipse. I was using AEM v1 for tuning so it might be a single issue and not the Ecu itself. I tried everything on these forums to correct the issue but nothing helped. In the end, I bought an aftermarket tach and it works great with no problems. Sorry I have no solutions/help but I thought I would share my experience. Good luck

Swapped back in, works fine with the original ECU.

Also, looks like dsmchips.com is closed...

I believe he still has those adapters around. he is not doing tunes from what I understand. Unless you want to change what you have and not a first time buyer