CEL always on, ALWAYS

[NolimitZ32]

Has anyone ever had this problem: I recently went through the whole car and tested all input/outputs on sensors as well as continuity and signal at the ECU plug. Everything checks out as it should per the FSM. The car starts and runs, holds idle (though a bit high ~950RPM). When driving it will behave normal from idle to ~3500RPM When I either go WOT (at any RPM) or get it up above ~3500RPM it starts to pull A LOT of timing to the point where its undrivable in these conditions. Back to the CEL, it comes on when the key is turned to the ON position and stays on no matter what, when I try to enter diagnostic mode it does nothing just stays lit it also wont show the O2 switching (Mode II) the CEL just stay on.

So anyone got any suggestions?

[robomatic12]

Bad ECU?? :/ Thats my guess, try a known good one?

[NolimitZ32]

Thanks for the suggestion, Ive tried 3 ECUs, 2 chipped, one NA and not chipped (cant run the car on this one but i plug it in and turn to ON) all 3 ECUs do this, the two TT units could maybe be bad (which they are most likely not), the NA is 100% good and they all do the same thing.

[nissanfreak12]

Curiousity, since its on, what are the codes? Have you deleted anything? I know you have checked all of this but maybe its something you have overlooked, happens to all of us. Other than a grounded out wire and what Robo said, Im at a lost as well.

[NolimitZ32]

All of the emissions stuff is deleted and the chip is written for the deletes, that's the thing I can't pull codes, the ECU wont go into diagnostic mode neither of the 3 will, the CEL just stays on no matter what I do. I though I overlooked something but I've been beating my head against this problem for a number of months now, every single elctrical connection has been checked multiple times so i'm absolutely clueless on what to do short of pulling the engine and EFI harness and going over every inch of everything by hand.

[nissanfreak12]

HOw are the grounds by the ecu? I am not too sure about the z32, but I know my old rx7 had solder points that would just fail, most were by the ecu, and it just did some funky things.

[NolimitZ32]

As far as I know (now I could be wrong but I'm 99.4% positive) that all the grounds are in the engine bay, as in there are none on the passenger compartment side but I will double check all my grounds again when I get back from the weekend. Thanks for the input, keep em coming.

[es.biggs]

Does the LED on the ECU just stay lit when you get into diag mode?

[CTNissanTech]

My 1990 300ZX TT auto is doing the same thing. cooling fans running when ign is on, doesn't matter if the car is running or not. idles high, runs extremely rich at wot or high rpms. MIL on, im gonna pull the codes (if possible) on tuesday. Hopefully i wont have to start chasing electrical gremlins.

[nissanfreak12]

My 1990 300ZX TT auto is doing the same thing. cooling fans running when ign is on, doesn't matter if the car is running or not. idles high, runs extremely rich at wot or high rpms. MIL on, im gonna pull the codes (if possible) on tuesday. Hopefully i wont have to start chasing electrical gremlins.

If for some reason no codes comes out, your problem screams Coolant temp Sensor. Hopefully you dont have too many wiring/electrical problems, those are never fun chasing.

[CTNissanTech]

UPDATE:

Just checked codes, ecu will NOT enter diag mode with pot screw. Also, cannot run "ENGINE" diag using consult-II, though "TRANS" and "HICAS" boot up during system call. LED on ecu lights up and stays soild. I'm guessing bad ecu, but ill do all the power/ground/continuity checks before i have to spend any money.

[NolimitZ32]

So I did have bad ECUs or rather one bad ECU and one bad chip, After mix and matching ECUs and Chips I got the car to run and boost, in the process I installed a new Coolant temp sensor and tested the TPS to find that it was not showing full range of function (it only output between 1 kOhm and 7.3 kOhm, instead of the 1-9 it should show). So pending a new TPS my car may be well on its way to being finally ready for the streets.

[nissanfreak12]

Good to hear you found the issue!

[CTNissanTech]

Thats great to hear. after checking all the fuses and the grounds i could get to, im confident an ecu will fix mine as well. Thanks for the updates.