At Putnam for the weekend and struggling. Car is falling on its face and feels like it's running on 4 cylinders. New plugs, wires. Fuel pressure at rail looks good at 58psi.
I believe its staying in Open Loop and not operating in closed loop. Engine is a cammed LS1 running GM PCM with speed inc tuning.
Codes remained cleared but showing no pending or active codes stored but one "Specific DTC" whatever that means for P0135. Just replaced MAF, denso O2 sensors and ECT and it is running even worse after reset. Used to run fantastic until the last few events and throwing parts havent done anything. Thinking maybe wiring but I suck at testing harnesses so might as well be magic.
Let me know if you have any ideas on things I can chase while I am here for the next 2 days hopefully getting her running better.
P0135 in the quickest, simplest search comes up O2 heater circuit problem: https://www.autozone.com/diy/diagnostic-trouble-codes/p0135-oxygen-o2-sensor-heater-circuit-malfunction
I don't know whether that includes the sensor, or is specific to the bits that drive it or monitor it.
Having a dead O2 sensor or related wiring certainly seems like something that could cause it to freak out and not run properly, but I know nothing about this application and not enough about whether that's actually a likely scenario for your symptoms.
I don't doubt you'll get more cohesive input here soon, but you might have a good look at any O2 sensor wiring and connectors you can lay eyes on.
O2 heater circuit could be a power problem to the actual O2 sensor, and I can see how the car would go into open loop if it can't trust the O2 sensor. That is specifically for bank 1, sensor 1 so you could test by swapping the sensors side to see and see if the same DTC comes back. If so, it's not the sensor but it's the power supply to it.
But the open loop tuning should be good enough to keep it from falling on its face, otherwise you'd probably see DTCs for things like big long term trims. So that doesn't explain the running. Do you have any way to check the relative temperature of the exhaust runners? Great way to diagnose a bad cylinder or two or three or four. If it's a whole bank, I'd be looking at the connectors on the wiring on top of the valve covers, specifically where the sub harness connects to the main (if memory serves).
Do you maintain battery power to the PCM when the car is off, or is there a whole-system kill switch? If the latter, leave it turned on for a couple of sessions and check the DTCs again. Unless Speed Inc really kneecaps the OBD system, it should tell you what's going wrong. If you have an HP Tuners interface, check to make sure someone hasn't turned off a gratuitous number of DTCs.
Thanks a bunch Mr. Tanner.
Swapped O2 sensor side to side and the ghost code didnt change. Then all new sensors no change (or worse).
Have a temp gun here so will check relative exhaust temps. Will trace O2 wires as well after the drivers meeting.
Two questions I have.
Is it using OEM style wiring or some swap kit wiring? OEM style wiring powers up each bank of coils and injectors separately, if one side is not getting power then it's going to run horribly. (This was intentional - if you lost one bank's coils, it will also thus not open the injectors)
Is it a stock cam? Some aftermarket cams do things like swap cylinders for a different firing order.
If it's aftermarket wiring, make sure it's for your firing order!
Other than that, check the basics - vacuum leaks, exhaust leaks before the oxygen sensors.
If it was running happily before, it's not likely to be firing order as that very rarely changes spontaneously :) Well, not non-catastrophically anyhow.
For the O2 sensor heater, check for fuses. But it's more likely to be a poorly seated connector or a toasted wire. You don't get a heater warning for a leak, that's more likely to be a lean reading.
Exhaust temps will be easiest to check immediately on start. A fast way to check is to get a squirt bottle and just spritz the runners to see which ones boil off the water. Heck, you can do it with a wet finger if you're feeling sporty.
Pete. (l33t FS) said:
Two questions I have.
Is it using OEM style wiring or some swap kit wiring? OEM style wiring powers up each bank of coils and injectors separately, if one side is not getting power then it's going to run horribly. (This was intentional - if you lost one bank's coils, it will also thus not open the injectors)
Is it a stock cam? Some aftermarket cams do things like swap cylinders for a different firing order.
If it's aftermarket wiring, make sure it's for your firing order!
Other than that, check the basics - vacuum leaks, exhaust leaks before the oxygen sensors.
Thinned OEM harness with DIY fuse/relay panel.
Car ran 4 or 5 weekends FLAWLESSLY before this issue surfaced which has me leaning toward maintenance or wiring short.
Do you have a TCU? Far from an expert, especially considering the company here, but my project came with a cammed LY2 in front of a T5 and went like a bat outta hell until the rushed wiring fried the TCU. Engine would have been in front of a GM auto (4L60 or 4L80, me thinks the 80 but it doesn't matter to me) and the ECU needed to see a CAN signal from the TCU or it went into limp. Capped my revs at ~4200, ran rich, and like a mushy version of what it once was. Limping along, if you will. Not sure if it applies to your use case but that's my 1c. Also, I'm fairly certain that TCU problems won't show up as such on OBD.
Otherwise I'd get a bright flashlight, a cold beer/hot coffee (switch at your peril), and start looking for obvious wiring problems. I say obvious because the symptoms given would point to change being the cause, something dynamic, and that would lead me to suspect anywhere that movement, motion, or heat could get at the wiring in the bay. Also, bad grounds. Either way, if something is pulling voltage down then you could be losing a lot more than an O2 heater circuit.
Check the grounds on your diy fuse/relay block- we've battled issues with that and wiring passing through the firewall on our drag car.
In reply to Olemiss540 :
D'oh! I was assuming it was a new swap.
If it still has a stock type tune, you can eliminate MAF and most vacuum leaks by unplugging the MAF and letting it fail out, so the car runs speed-density strictly by the MAP sensor. A speed density car will run a lot better with a vacuum leak than a MAF car will 
I think the O2 heater fault may be a clue that there is a ground fault somewhere.
Grounds are a good suggestion for sure.
All of my grounds are terminated in easily accessible areas in the cabin (around the tranny tunnel) so I dont know how it could be a ground issue but DEFINATELY leaning towards an electrical gremlin.
Guessing a short somewhere. Found an issue in my (old) kill switch where the fuse block power was strangely loosing connection with the slightest vibration. Fixed that and was certain it would lead to success but still having an issue.
I HATE electrical diag.
The 2 brand new O2 sensors reading low like 30-45mV on idle. Car running WORSE with the new ect/O2/Maf to where it wants to die with any throttle now.
Fuel pressure solid at 58lbs per Corvette fpr.
Low readings on O2 sensors at idle could be explained by a heater issue. I think your code tells you that.
I don't THINK it's a closed loop heater on these. It's probably just a solid 12v. Easy enough to check to see if that's present.
In reply to Keith Tanner :
The stock wiring ran the O2 heaters full time, from the O2 heater fuse in the underhood fuse block right to a ground splicepack.
Easy enough to check with a voltmeter. O2 sensor should have two white wires, one should have 12v between the wire and battery positive and the other should have 12v bewteen the wire and battery negative. (I do not like using ohmmeters to check ground)
That's exactly where I am leaning.
Will figure out a way to check this week to see if I can solve this before trying to bribe a shop into taking on my mess......
Car is at the shop, will update once resolution is (hopefully) found.
Now wondering. My car has always ran fabulous and stayed COOL compared to my previous cars. Even mid session the coolant temps seemed to stay in the 170's - 180's with the 160 degree thermostat.
Maybe this was too cool and eventually caused the PCM to go into some sort of limp mode due to under temp. Just my ramblings but let me know if anyone has any background knowledge possiubly even specific to the 2004 GTO that i used the PCM off of.
In reply to Olemiss540 :
If the coolant is undertemp, it will run normally, set a P0128, and kill the coolant temp gauge.
