nealnanoHX

So I failed emissions for no communication due to my OBD1 conversion on my 98 Civic with LS Vtec swap. I swapped out my P28 ECU for my old OBD2 P75 ECU that I saved for this exact reason. All the monitors have passed but the catylist monitor. I have put 150 miles on the car and it still has not passed, did a lot of highway driving at 55 mph, did a bunch of stop and go at 40-45 mph and did some high speed driving taking it up to 70 mph. Did not want to push it too much without the right tune on it. Are there and tips or tricks to getting the cat monitor to set????

Former User

Secondary O2 sensor? Is it real?

nealnanoHX

Yes and yes. Everything is there and hooked up for this car to be fully OBD2 from the ECU to the dizzy to the EVAP system, OEM OBD2 99 Si cat, rear O2 sensor and the CFS. I have owned this car for many years now and did the B18B1 swap myself and did it fully OBD2 and it passed emission 4 years ago as a OBD2 B18B1 swap. I did the Vtec head swap on it and the OBD1 conversion which is just the harness adapter and ECU. I now have The P75 running the car and it runs fine just no Vtec and way down on power, 161whp to 116whp as per Dynojet when I had the stock B18B1 set dynoed and the tuned LS Vtec dynoed and no CEL and no codes pending. The emissions laws changed where I live and 2 years ago I could pass with my OBD1 conversion since the CEL turns on and off and there are no codes but now they have to be able communicate with the ECU so since I went threw with the OBD1 ECU that was not happening and they failed me. All my other monitors have passed just need to get the cat monitor to pass, please any tips.

Former User

The ECU monitors the cat by comparing the primary and secondary O2 sensor outputs. Perhaps you should test both sensors, especially the secondary one.

nealnanoHX

I watched them in the data and they are both looking good and responding well. If there was an issue with the O2 sensors it would not have passed the O2 monitors and would have posted a code for the bad O2 sensor or a cat efficiency.

Former User

Bad O2 sensors don't always throw codes.

But if they're both responding well, then check whether the Back Up fuse is blown. The problem could also be a bad ECU.

nealnanoHX

No blown fuses if the back up fuse was blown I could not read the data with my scanner. This is a good known ECU. As I said I used it on my car before I did the OBD1 conversion and it passed emissions before.

Former User

Not true. You're thinking of fuse 43 for the DLC circuit.

Not a water tight argument -- That was then, this is now.

nealnanoHX

Well I just went to emissions and it passed finally. So I guess it was a good ECU no reason for it to go bad just sitting on a shelf. So nice to have my tune ECU running the car again, Vtec YO.