Appologize for the double post not sure how to delete thread…

I need some guidance… been having an intermittent code 28. CEL is super random. I would start the car and the light would be off and then proceed to drive about 5-10 minutes for it to come back on. Other times it will just be on from start up and stay on. Sometimes I would start the car and leave the car idling for 5-10 minutes with CEL off, then shut it down…restart then see CEL light on. Here is what i have replaced/installed so far.

- Installed new main o2 sensors both sides (denso)
- Installed new Spark plugs and wires (denso)
- Interchanged MAF and ECU from my other sc400 that are known to be in working condition

Car runs good, dont really recognize a power loss (comparing it to my other sc400), but I believe the car is running a little rich.

I think it could be just down to be a short in circuit but I'm not entirely sure. If I were to test connections with Multimeter where should i start first? Any leads on ground location? Any known common locations of bad grounds? Could a potential exhaust leak cause this type of issue? Open to any guidance!

THANKS!

 

I would start with verifying if you have the correct O2 sensors, assuming you only have 2 and you replaced the pre-cat ones. I think you may have a 2 wire vs a 3 wire, but I may be wrong since the transition to OBD2 makes 94-95 models unique in a way vs OBD1 91-93 models and OBD2 96+ models. Besides that I would check their respective wiring and ensure they're not damaged in any way, either by touching the exhaust and melting, or the clip coming undone for whatever reason. Once those are verified I would check the grounding point on the ECU since it's probably the only ground that works through the Oxygen sensors. If all those are good, then maybe have a look at the ECU, more than likely it will be the ECU, but check free first.