1989 240sx w/ka24de swap cel stays on and won't throw code

[scolobey]

I have a 1989 240 w/ a ka24de swap.the previous owner did the swap and did a crappy jobnow the CEL stays on. I tried to read the code, but I can't get the ecu to access diagnostic mode. I turned the screw clockwise and counterclockwise and clockwise again with the ignition on but engine not startedThe light on the ecu just stays onalready failed smog once, and this was one of several reasons

what would cause the ecu to be unable to enter diagnostic?

[180fan]

a bad ecu could keep it from going to diagnostic.

What other reason did you fail smog on? I'm already almost certain NOx was one of the reasons.

[benemorius]

Have you pulled codes before or is it possible that you're not doing something quite right? (just to be sure)

Welcome to Nico, by the way!

[scolobey]

I have never succesfuly pulled codes before. I went by the fsm instructions.I unbolted the ecu and flipped it around so I could see the light. Turned ignition to on position without starting the engine. Then moved the screw, then waited three seconds, then moved it back. Also tried some other random stuff and pretty much any combination I could think of and the light always stayed on if the ignition was in on position.

Thanks for the reply and the welcome

[scolobey]

you are correct sir. I got 1228 on NOx @ 15mph and 989 at 25mph. Max allowable is 799 and 738 respectively. HC and CO were within specs although they were higher than average. The guy also said that the timing was off. Which was true. When the tps was disconnected, timing went from 20 btdc to way off. I got a new tps and that seemed to fix that problem. I just scored an ecu the other day, but it's for the sohc. Is it possible to use that one or should I start looking for the dohc ecu?

thanks

[benemorius]

Yeah I hate all the instructions that just say wait X seconds. You should be able to find better instructions if you search the board.

[180fan]

Warm up the engine fully first, then with the tps disconnected then check the timing. Adjust as needed. Advanced timing will send your NOx through the roof as I'm assuming you've got 150k+ on the engine and probably never had it cleaned for carbon deposits and other junk that's keeping the cylinder temps higher than they should be. Do not use the SOHC ecu for a DOHC.

[NISTECH]

I have to wonder if you have a sohc ecu in there and thats part of the problem? When you try to access diag mode do the lights inside the ecm flash at all when changing the screw position?

[scolobey]

the lights don't flash at all. I don't think the ecu is sohc because it has only one light. However, when I first tried to pull codes I was going off of the sohc instructions, which specify two lights. I took the ecu apart and soddered in a second light because there was a spot for it (dumb, I know) But it didn't work before that so that didn't break it. My only thought at the moment is that I need to find a new dohc ecu . Is it possible that a wrong connection could cause the light to stay on? Or is it most likely a problem with the ecu?

[scolobey]

yeah, I did all that, so the nox might actually pass by now, but the cel won't go off when I start the engine. I'm just gonna check all the connections and try and find a dohc ecu. Any other suggestions?