So I bought the car in December, its an '03 g35 coupe. I rented a uhaul truck and trailer because the car was 3 hours away. Backstory from previous owner was that he couldn't pass inspection and had bought an sti so the car had been parked for several months. Over the course of owning the car, I kept it in my parking lot and fixed a bunch of cosmetic things (bumpers, not working sunroof, oil leak). Last week i finally registered the car and took it out for a spin. Car has a slight misfire once its reaching operating temp. The first day i drove i can feel a misfire/bog from 1-3k rpm's. After that, car would pull fine. I thought it was bad gas since the car sat for so long and the tank was on E. I filled up tank and drove it some more. After driving it the second day it didnt bog but it felt like the car would misfire at idle. I pulled the codes and this is what i go after driving just two days in a row:

-P1148:
closed loop bank 1
-P0300:
Random-multiple misfire detected
-P0138:
Oxygen sensor circuit high voltage bank 1 sensor 2
-P0158:
Oxygen sensor circuit high voltage bank 2 sensor 2
-P1276:
Air fuel sensor 1 heater bank 1
-P0158:
Oxygen sensor circuit high voltage bank 2 sensor 2

the rest are the codes mentioned above but PENDING.. I did change the oil and spark plugs prior to registering the car. From what i can see the previous owner deleted the cats and car also has an intake. I ordered some ARK high flow cats and pray the car will read the air fuel better. Any suggestions??

 

Those bankXsensor2 ones can probably all be fixed with non-foulers on the test pipes (or by switching back to a HFC). If the airflow is too great with the test pipes and there's shitty geometry where the downstream O2 sensors read then you get those codes. Non-foulers are usually the fix, sometimes it takes 2 sets, you just need to move the sensor away from the stream of air shooting down the pipe.

Multiple misfire can be a lot of things, pull all the plugs and make sure it looks like they're all firing. What plugs did you use?

Looks like your bank1sensor1 O2 sensor (the upstream one) died.

Check for any exhaust leaks, that can really screw up the system as well. Have a local reputable shop do a smoke test or do it yourself if you have access to a halloween smoke machine and a shop vacuum.

 

I used the nkg iridium

Are Denso sensors good for our cars, or go with Bosch?

I'll get under the car this weekend and see if anything seems abnormal, thank you so much!

 

Usually I try to use all Bosch fuel components (including O2 sensors) and everything else Hitachi. Both are solid brands.

 

OK so I replaced the Bank 1 sensor 1 and cleared the CEL. Drove the car and its still sputtering really bad between 1k-3k RPM, after that it pulls super smooth and hard. I searched around and read that the PCV valve may cause this so i replaced the valve. Drove the car after replacing it and it ran beautiful for about 5 minutes and back to the terrible idle and bad hesitation and sputtering. The 02 sensor i put in and the PCV valve i purchased from the dealer.

Also while it was idling rough, i pulled each coil and they all seem to be fine (rough idle got worse every time i pulled the plug). Did the same with MAF sensor, seems to be good. I also reset the idle right after i replaced the PCV valve, and like i said, car idled beautiful and was accelerating just fine for about 5 minutes. Now I'm back to square one. When i parked the car, check engine light came back on so i ran the codes. Now instead of 11, I'm down to 6 codes.

-P0138
Oxygen sensor circuit high voltage
Bank 1 Sensor 2 CONFIRMED
-P0158
Oxygen sensor circuit high voltage
Bank 2 Sensor 2 CONFIRMED
-P0138
PENDING
-P0158
PENDING
-P1278
Air fuel Sensor 1 Heater Bank 1
PENDING
-P1279
Air fuel Sensor 1 Heater Bank 1
PENDING

I'm not sure why I'm getting the Sensor 1 heater bank 1 code since i replaced the 02 sensor and inspected the wires and everything looks fine. The random misfire code did not come back but the sputter is terrible, just as bad as a misfire. Also, for the bank 1 and bank 2 sensor 2, i ordered high flow cats, I'm hoping that fixes those two codes. If anyone can point me on the right direction for this hesitation and terrible idle please let me know. Really appreciate it!!

 

I was going to suggest removing the cats and i specting them to see if they're melted but if it pulls hard past 3k with no problem then I doubt it's the issue and I'm suspecting a cam sensor failure.

I recommend at this point to go pay Nissan for a 1 hour diagnostic because they can watch the cam/crank sensors with an oscilloscope. Be sure to tell them you already replaced that upstream sensor and it's still throwing a code.

I can't think of any other good reason it would be misfiring only between 2-3k rpms.

 

wouldn't the cam sensor throw a code?

I'm going to remove the cats it has now to inspect until the high flows come in on tuesday.

 

It will throw a code when it has a dead short, an open circuit. I suspect it's simply sending a wrong signal during a certain range which is causing the ECM to make the wrong fuel and ignition pulses between those rpms.

I would also clean the MAF, just to make sure it's not the culprit and if it hasn't been done lately it's probably due anyways.

 

UPDATE:

So i bought Uprev software and cable to run some diagnostics on the car, and after testing voltage and continuity following the FSM, it seems to be the engine harness. Tested everything and when it came to the 02 sensors, for some reason there was no continuity. Probably explains why i kept getting the codes after the sensors were replaced. These are the codes that came up...



Right now I'm in the process of sourcing a used engine harness. Need a 2003 6speed manual coupe harness. If anyone has one please message me so I can finally get this car running 100% !! Thank you

 

First thing to do is unplug the ECM, the O2 sensors, and verify the circuit is indeed incomplete or grounded out. There might not be anything wrong with the harness and you need to troubleshoot it before replacing anything.

Keep in mind you can also just run new wires from the ECM down to the O2 sensors rather than replacing the entire harness. Put them in their own wire loom and run some SXL wires down there, use quality tie wraps (ones that are UV rated) and Super 33+ electrical tape to tape it to the existing harness and stay away from close proximity to any heat sources like the headers/exhaust pipes.

I would simply cut and solder splice the wires at the ECM, leave a tail about 10-12" long or so, then crimp a cap onto the abandoned wire and leave it. Do the same thing at the O2 sensors then use a DMM to verify continuity.

 

Jeez I didn't think of that.. I already removed the harness. When i was inspecting the wires by the ECM a lot of the wires were exposed and taped up. Here's an example.

 

Yuck, well looks like your found some of the problems.

 

UPDATE:

So i sourced a good harness and installed it on the car. Car still has the same exact symptoms. and the same codes came back up. I am leaning towards the ECM now.



Now, before I wasn't getting the U1000 code only the U1001. So Im assuming because the previous harness was hacked, maybe it fried or shorted something out on the ECM.



According to the FSM it says it's either the connector or harness, but harness has been replaced. Also, all those 02 sensor codes are not the sensors since i put new sensors.
The FSM also directs to do the following troubleshooting...




I've done the idle relearn and nothing. I also replaced the CMP which is the cam sensors (replaced both driver and passenger). The CKP i haven't replaced, but as you can see it suggests to replace ECM. I'll try that out and hopefully that does it.

 

[QUOTE=BadG35M;7169772]UPDATE:

So i bought Uprev software and cable to run some diagnostics on the car, and after testing voltage and continuity following the FSM, it seems to be the engine harness. Tested everything and when it came to the 02 sensors, for some reason there was no continuity. Probably explains why i kept getting the codes after the sensors were replaced.

Are you getting continuity at the sensors now with new harness? Do you have a way to see the o2 voltage with scanner while car is running? I’m having same issue/same codes. I also installed new sensors.

 

Figured it out on my g35. It’s definitely your ecu. Our 2003 ecu should not be looking for 127*-1289 codes because those are for the newer sensors. When I pulled my ecu out it had 2004 350z written on it.