Hi everyone! I've finally come across the time that I cannot diagnose my own car. I need some actual help now from more experienced people.

Here's my situation and a backstory. I will be going into detail with all of the diagnostics I've done so it can help you guys understand where I stand.

I have an 5.3 swapped Nissan 350z, cammed, lth, ls6 intake, and E85. It is also on a 225 shot of nitrous. Recently, I decided to up the shot to a 250 shot, and long and behold, it backfired. It blew out the maf sensor, intake tube, and shredded my air filter. I was able to drive the car back home without all 3 items. Surprisingly, the car drove back just fine. Cruising afr were at a 14.7:1, but would richen up if I step on the throttle a bit more. It would be around 11:1 to 9.5:1 at heavier throttle. Didn't worry much as I'm missing the MAF, figured its normal.

Got the car back home and replaced all 3 parts. I bought a Delphi MAF sensor from AutoZone and the other two. Once I replaced the maf, figured out would be okay now. Drove around and same thing, cruising around, the car drove fine. It was still at the 14.7:1 range and when I gave it more throttle, same rich condition, 11:1 to 9.5:1 ... From that alone, it would make sense that other things might have gotten damaged, such as the O2 sensor and my MAP sensor. I went ahead and bought a GM O2 Sensor from Amazon and a Duralast MAP Sensor. I also did a compression check and smoke leak down test, both checked out just fine. No vacuum leaks at all.

When I replaced the O2 sensor and the MAP sensor, the car then started being rich at all times. Idle is now sitting at a 12.5:1 cold to 13.5:1 warm. I tried to see if the O2 sensor needed some heat cycles? (I have heard that it was a thing? I doubted it but it was worth a shot). Car still progressively gotten rich with slight throttle and it could only get worse from there. Car also misfired on idle.

I had replaced the AutoZone MAP sensor back to my old MAP sensor and that has fixed the misfires at idle but my rich condition remained. I have been thinking that I should replace the O2 Sensors back to my old one? But I have yet to do that. I wanted to figure out why its rich at all times now, in denial about the chance of the new O2 sensor being a bad unit.

So I had started troubleshooting my fuel system, I went ahead and checked my fuel pressure and it started at 40psi at Key ON Position and quickly dropped to 20psi. I had thought I got my issue from there! It's on a returnless set up, and Nissan 350'z fuel pump assemblies have an in tank regulator. It being a returnless set up, I only have a few parts to check out. I started with checking my injectors and I was so sure that it was probably stuck open or closed. Pulled and had them testing, just for the tech to give it right back as it was perfectly fine... I had just gotten a brand new fuel pump assembly so I know for a fact that my fuel pump and the in tank regulator was good. I realized that I was near E on my gauge, so I added some E85 and voila, pressure at Key ON was at 40psi and held! Started the car and fuel pressure at idle was 50psi and held. I know that stock LS fuel system runs 58psi. I may have a weaker voltage and I have my hotwire key collecting dust, which I'll probably install in the future.

Now I'm out of ideas as to why my car would still be running rich? I have a theory that maybe my Z got tuned with some issues and now I have replaced some sensors, it needs a new tune to run properly again?

I could really use some help from people that can read datalogs. My STFT stays at 0% and LTFT are at -1.6% sometimes. If my car is running this rich, shouldn't my STFT and LTFT be at over +10% trying to correct the balance? This is exactly where I'm stumped now.

I'll attach a cold idle log, warm idle, and a slow drive log. I would greatly appreciate it if someone can take a look at it and make something out of it.

ALL OF MY DIAGNOSIS SO FAR
- Check Coolant for possible head gasket issue due to backfire
- Check Oil for gas or coolant
- Smoke Leak Test for Vacuum Leaks
- GM O2 Sensors from Amazon - MAP Sensor: Good
- Check for Fuel Pressure: 40psi Key ON // 50psi IDLE
- No Pinched Fuel Line
- Fuel Pump is Good
- Injectors are in proper working condition
- Compression check are the same across the board

 

You are only getting a default phantom voltage reading on your o2 sensors, so the computer is not going into closed loop. The 0 STFT and 1.6 LTFT are just leftover artifacts of the last time the o2 sensors were working. You probably have some broken or melted wiring somewhere.

 

could that also mean that my current o2 sensor was bad? I was thinking of throwing my old o2 sensor to test.

I did also force the ecu to go into Closed Loop using HPT and it started leaning out into like 15’s:1 AFR. I saw upwards of 15% on the stft.

 

For both banks to start reporting nothing from the o2 sensors would require a crazy coincidence of both sensors going bad at the same time, or much more likely a wire problem. I strongly doubt any of the o2 sensors are bad. I am confused by your use of the singular "o2 sensor", rather than plural. You are showing no real reading on bank 1 or 2. Since this is a swap vehicle, I have no idea what your wiring situation looks like.

 

I totally understand, I will look under the car for any wiring issues then. Maybe the backfire had caused some damage under there. But also, yeah, I meant o2 sensors.

 

Have you checked to see if you have any DTC's? If so, that could be keeping it going into CL. But IIRC, it should say OL fault if there is.

As gametech said, there's something going on with the 02's. The 02 voltage staying around 450mv is normally an indication the sensors aren't plugged in or a wiring issue.

I can see the commanded EQ in the log, but don't see the actual WB, your PID layout is kinda hard to follow.

 

Hi! Apologies about the PID. I’m new to HP Tuners so I just turned on whatever parameters I will can help me out lol

Also, I have checked all the wiring just now and there are no issues with it. I do not see any breakage, I was hoping it was just that but unfortunately the wiring looks just like how I put it on during the swap.

The car only has the upstream o2’s so that’s why I can’t show the WB readings on HP. But that’s also why I’m not throwing any CEL code, my tuner might have turned it off?

I’ll keep on digging deeper to see if there are any wiring issues.

 

Moderator Note: I merged the OP's two threads; hence there is some duplication in posts.

Hi everyone!

Need some professional help. My LS 350z is not getting any o2 sensor reading from the ECU. On HPTuners, it is stuck at 450mv.

First I changed the O2 sensors since I had brand new Delphi sensors anyways. Didn’t fix it.

I checked the wiring on my ECU pin and wiring are all going to the correct terminals, and have good continuity on the Tan and Purple wires. 12v on the pink wire is also good on voltage, and same with ground. Physical wires are in perfect condition, no pinched wires or broken/cut wires.

I don’t know what else to do… Could be that my ECU went back on just the O2’s? I don’t have another ECU to try out but I’ll probably start looking for ECU’s to try out.

The ECU is out of a 2001 Camaro Z28 - I’ve looked into Case or Isolated Ground O2 Sensors and I know my wiring harness is built for an Isolated O2 Sensor.

The car worked flawlessly before then I had a Nitrous backfire that ruined my maf, intake tube, and air filter. Ever since then, my O2 sensors stopped working.

Any other suggestions, please let me know as I’m stumped.

I had posted before with logs if anyone wanted to take a look. Here is the LINK to that old thread I had created.

 

Sounds like you have done all the correct troubleshooting. Please confirm:
1. The new O2 sensors have the same plug as the old ones?
2. You unplugged the sensors and got 12V and Ground at the connector?
3. You confirmed continuity of the two signal wires from the connector back to the ECU?

(I know stupid questions after your detailed post, but since no replies in 24 hours, everyone else is baffled too.)

Where did you buy the O2 sensor? Reputable?

I ponder how a Nitrous backfire could damage the O2 sensors in the first place. But then how could it damage the ECU too?

I suggest all members add their city to the profile. It makes it easier for someone nearby to help you.

ANYONE - Sorry I don't know this, but will an O2 read 450mV even if disconnected?

 

1 - O2 Sensors indeed have the same plugs
2 - All the multimeter tests were done with the O2 sensor unplugged. Pink Wire gets the proper 12v and Ground is good on the pcm, also made sure ground is solid on all of the ground points in the harness.
3 - Both Signal, High and Low Wires, have continuity. Reading at 0 resistance on my multimeter as well.

I have tried 2 different sensors, a GM Genuine Brand from Amazon and a Denso. Both unfortunately did not work. I did contact Wiring Specialties as they made my 350z LS Harness and provided my ECU, they have mentioned that it could just be the wrong type of O2 sensor. I finally have a Part Number for an O2 sensor, and I am PRAYING that solves my issues… If not, then I’ll be trying a new ECU and pray it solves it lol…

To answer your other question, 450mv is a default voltage if there are no O2 sensors are plugged in…

But that’s where we’re all confused by my post. I’ve done all my diagnostics and wires are checking out to what they are supposed to be doing, yet there’s no reading at all? That’s when my harness builder said it’s probably a wrong O2 sensor.

I will be updating my post with what happens, as someone might get some answers from my detailed post.

I appreciate your time replying!

 

The engine is not going into Closed Loop. You are stuck im Open Loop and the O2s are acting properly because of Open Loop.
Check your Tune for when Closed Loop gets active. You are only hiting 76 Degrees Coolant Temp so maybe you need to check that value in the Tune for Closed loop

 

Even in Open Loop, I should be getting O2 sensor movement right? Like shouldn’t it still be oscillating?

I’ll check my logs again for the coolant temp, but even driving the car around at ops temp, it still running rich. Granted I did not log any of those.

I also tried to force the car to go into Closed Loop and still had no O2 sensor activity. Forcing CL would make the car run lean, like 15:1 or so. Which I would guess is normal because of the rich condition.

 

I stand corrected, you are right there should still be some movement in Open Loop.

So this means you have a wiring issue/ no connectivity somehow with the O2's

 

Yeah, that’s where I’m stuck unfortunately. Both high and low signal wires have good continuity and there are no broken wires. The harness builder suggested that I may have just been using the wrong O2 Sensors but I’ve tried two already. I’ll give the suggested Denso 234-4087 a try, and if that doesn’t fix it… It better be the damn pcm at this point…

I know for a fact that its not wired incorrectly or anything as it was working before.

 

As far as I can tell, there aren't that many different narrow-band O2 sensor. Mostly just connector and length. I don't know if identical connectors ever have different pinouts.
Hopefully your new sensors will work.
Can you share what part numbers you have so far, including the non-working ones. And what you have coming.

 

That’s why I think it won’t work… But I’ll keep my hopes alive lol

GM Genuine #12640453
Denso #234 4025

^ Those above did not “work”

I know the sensors are all working as I did the torch test and saw voltage.

The one that my builder provided will be the Denso #234 4087

 

@yolandosm - You started a second thread, which was very confusing and may have annoyed some of the people looking to help you. Therefore I just merged the posts into one thread, in chronological order.
Moderator.

 

Well guys! Denso 234-4087 worked for me! It’s oscillating as it should, verified by my scanner… But how fun would that be if there’s no other issue…

Started the car and it ran for 10 seconds and something shorted out :/ PCM is completely toasted as it wouldn’t connect to my scanner anymore and car would not crank at all.

I happened to have a spare pcm and plugged that in. It cranked over the car, but that pcm is not tuned. So I’m in talks with my tuner so he can flash this other pcm with my tune file.

I’m praying that the pcm was just on its way out and it finally stopped working completely? Last thing I want is to flash this new pcm my tune, start the car, and it shorts out again

I’ll keep updating the thread if it gets completely resolved.

 

Sorry to hear; that really sucks.
I do wonder if there is/was an underlying problem which prevented the other O2 sensors from reading, that problem briefly went away with the new Denso, and then came back with a vengeance.
It might help you to know if the PCM still has power; maybe it just lost power.'

 

It’s bricked for sure. I have a spare pcm and it powered the car but obviously that pcm is not tuned so I couldn’t get it to fully run but at least o2 sensor reads. I did see some burnt wiring look but its the BCM harness. Maybe it backfed somehow to the pcm??? Could be that they share the same ground or something. But at least I’m close to getting it running again…