It's an 89 Civic SI. I've replaced the o2 sensor, spark plugs, and put in the oem ECU because the previous owner swapped it with one from an early 90s Integra. Anyways, the new ECU works fine but the light on top for you to check codes is broken. Is there any other way to see what codes are being thrown?

 

You need an OBD I scanner. That will allow you to read the codes.

 

An OBD1 scan tool won't do much good on an OBD0 ECU, not to mention that it's well established that OBD1 scan tools don't hook up to OBD1 Hondas.

OP, you put a PM6 ECU into the car, correct (check the label on the side of the case)? It may be possible to replace the LED, or just jumper something off the leads; I've not tried this myself. I've also never run into an OBD0 ECU with a busted light, so while it's not impossible, I wonder if not all is well inside there. Did the car have issues with the Integra ECU? Why did you swap the factory type back in?

 

I swapped it because it was causing lots of blackish smoke out the exhaust which meant it was running rich. It also would not idle correctly.

 

It should run rich on the teg ecu, but I'm surprised it ran that poorly. I'm nervous there's more going on here, but without codes it's tough to know where to start. Any chance of getting another ecu to check with?

 

I may just have to buy another one. It's an 1989 SI. The ECU code is 37820-PM6-A080. heres the inside of the ECU. Does everything look right?

 

It seems that the board has a light but it doesn't line up where the ECU cover is... Could this mean I got shafted?

 

Willing to pop the cover and get a picture of the board? Can compare to one of my collection.

 

I thought I akrealr posted a pic of it but I think it has to get approved first. I'll pm you

 

Looks like you got the right board. I have a PM6-A09 to compare, yours appears to be a prior revison (the sticker on that green plug tells you, can't see enough of it in pic), but most of the board matches. With the cover off can you tell if the light's working?

ref to explain ecu part codes, you may want to bookmark:
https://www.hondata.com/tech-ecu-identification

 

It only flickers once when you turn the key to the on position. And I don't mean a code flash like it's just a flicker of light and then it doesn't do anything else.