Been having a o2 problem as well as a misfire on the driver side for a long time even after replacing almost all of the ignitions components.

Been trying to trouble shoot for a while and im not sure what else there is besides the ecm.
Tested everything and gathered data threw tunerPro
(Things ive checked and tested)
-Both sensors replaced
-Driver side stays stuck at 450.mv, Left works properly
-Swapped sensors to opposing sides and problem stayed on driver side
-Rewired Driver/Passenger to ecm (wires looked burnt and cut up)
-Driver side still wouldn't read(stuck at 450mv)
-Grounded out both side to check wiring(Driver side still would not read or move Mv) [passenger side works and reads 4mv when grounded]
-Re did o2 sensor ground to frame
-checked again and Driver side o2 would not read Stuck at 450mv


Im not sure what else could be causing this not to read or register. This has been causing a misfire and has been giving me a headache since i got the car. The misfire doesn't start until around 180* im assuming because the car is stuck in open loop and that sensor isnt reading right.

Any help id greatly appreciate it. Thanks! 1992 vette

 

Sounds like ecm replacement / substitution is next step. All 92 -93 LT1s use the same ECM unfortunately they are hard to find and even used they can be pricey. You will likely have to send yours to repair facility and have it reconditioned.

 

How do you know it is stuck? Can you probe the wires and see what it is reading? Sounds weird.

 

I am using a aldl cable into my laptop and tunerpro data scanning so I am able to view the voltage coming into the ecm.

I can’t think of or know of any reason that the ecm would be blocking the signal beside a faulty ecm. The only other factor that I know of could be a bad adx. File. If anyone knows of any other scanner program I can use let me know and I will try that route... I still suspect the problem to be related to the o2 sensor because the car won’t enter closed loop and the misfire still occurring on the driver side.

 

If you pull the plugs do any show abnormal condition?

 

0.45V sounds more like a post cat voltage. Can you probe the sensor itself and see what voltage you are getting?

 

Pulled the sensor and bench tested it, put it in a vise and grounded the sensor and checked voltage. Lightly hitting it with a torch will show fluctuations in voltage between .20v- 1v. So I know it’s good and working also re-check wire continuity and shows good. Plugs are new and show nothing abnormal. All have a light brown haze and no smell of excess gas out the exhaust. The .450 volts out of a o2 shows no signal or not active. The thing is it’s a 1 wire non heated sensor and only has 1 on each side pre cat. Everything passenger side works and reads right, something to do with that driver side o2 is causing all sorts of problems

 

I'd disconnect it and see if the value changes. It might be that it doesn't read till it gets to light off temperature

 

Hello again aklim, et al
What you are seeing is exactly what aklim was pointing out, that you are seeing the two outputs for the One Side of the engine. The one bouncing is the Primary/Upper Pre-cat Oxygen sensor and the more stable signal is going to be the Down Stream/ O2. The rear are frequently more stable but the primary oxygen sensor should oscillate between .1 and .9 Vdc. The oscillation is so fast you need special tools to see what it is doing. That is why you now have data to see what the left side O2's and the Right Side O2's are doing.


I was taught that you should Always replace Both Oxygen Sensors on a side at the same time. If you have a "left side" and a "right side" then you might have up to four O2's in your Corvette It is more expensive but keeping them all on one schedule I would replace all at once. The factory replacement schedule is for 24 months or 50k miles on the earlier Non-heated type Oxygen sensor. I had an O2 fail and put my car into "Limp Mode". Older Oxygen sensors start to develop a narrower signal, In the beginning it would oscillate from .1 to .9 vdc and as they age the signal starts getting narrower send something like a .3 to .7 spread versus the wider .1 to .9 we see when they are new. The signal also slows down and cause problems for the ECM with its data output slowing down excessively.

Your Corvette will run more efficiently and the performance will increase while saving you some money all for a $20 part and a half hour of your time.

 

Yes,I understand what is being said I guess I forgot to mention that there is only 2 oxygen sensors in the car,(only pre catalytic converter)

91 L98 and 92-93 LT1 had two, both before the cat.
94-95 LT1 had three, one on drivers side before cat, two on passenger side one before,one after the cat, they were also heated electrically
96 LT1/LT4 had 4, two before and two after(each side)the cat.
LT5 had two heated sensors both before the cats.

I am using a data scanner so I am able to view voltage output in numerical as well as graph form. Still no movement or any sign when car is on as well grounding out the o2 wire still won’t show and movement on driver side

 

Just to clarify this aspect: the car is in open loop until it warms up, and thus isn't referencing the O2 sensors at all until then. However, once it enters closed-loop mode it starts referencing the O2 sensors, and you get the issues you're describing.

I strongly, strongly doubt this an ECM problem, since you have zero other symptoms and in fact the problem you describe sounds like the ECM is accurately reading the O2 sensor signal but the signal itself is faulty. There can literally only be two causes: the sensor (even though new) is still bad, or the wiring between the sensor and ECM is bad. I'm not familiar with the connectors and harness for your 92 C4 (I had a 96), but I'd try to probe the wire at the harness connector and see if you still get flatline voltage there. If so, you know it's not the ECM. I know you've seen voltage changes on a bench, but you could always swap sensors left to right to see if the problem follows the sensor. If it doesn't (i.e. if it stays on the left side) then you know it's not the sensor, either. At that point, it has to be the harness wiring. A final experiment could be bypassing the wire in the harness by running a different wire and tapping into the harness connector or into the wire just before the harness connector. If it runs well at that point, then you know it's the harness wire that has a short or discontinuity.

 

Ill list my step in my trouble shooting process to help make a little more sense
-Replaced 02 sensors just for routine maintenance along with other things. injectors,opti,coil,fuel filter, fuel pump,spark plugs,plug wires,iac valve,waterpump,fan motors along with a bunch of other misc things really anything i could (just bought the car Previous owner had problems with the vats so it sat for a few years)
- Before and after replacing all those parts a misfire/stumble at idle was always present
- Wanted to get into tuning/logging the car myself so had myself a early Christmas at maots(aldl cable,Ostrich 2.0, some other stuff as well)
-First noticed threw data logging that the driver side 02 wasnt reading right stuck at 450mv. As the passenger side was working right
-Made sure wires weren't corroded, bare, or bent/broken.
- Still reading 450mv
-Swapped 02 sensors to opposing sides (still no voltage change on drivers side
-pulled both o2 sensors and bench tested ( both tested good .2v-1v)
-disconnected/pulled 02 pins out of ecm and ran external wiring to the o2 sensors
-Driver side still stuck at 450mv ,Passenger side moved within range
-checked 02 sensor ground (came out good)
-Decided to cut 02 ground wire and run to frame ( after that re checked readings and passanger side worked properly and still no reading from driver side)
-After repining with external wires to each o2 sensor i then decide to check for continuity in my new wires just to be sure
-Disconnected and check with out problems tested good
-With the wires pined into the ecm and unplugged from o2 sensor i took the o2 side and grounded it out to check for ground signal on the ecm side.
-Passenger side after grounding dropped to .4 showing good wire and ground
-drivers side check and no voltage change when grounding out the 02 side of the wire. But when i back probe the wire ecm side it shows the drop to .4


After all of that im not sure what else could be stopping the 02 reading and not allowing it to work right. From wiring diagrams to plenty of reading i cant find anything else that is in relations to the driver side 02 sensor.

Im sure this is the problem that is causing the misfire at operating temp, as well as not allowing it to go into closed loop mode.... If one of the o2 sensors doesn't read right or shows not there 450mv the computers closed loop timer runs out and keeps it in open loop. I was wanting to keep the original computer systems on board for as long as possible, but the car is slowly turning into a track only vehicle. Im stuck between trying to tune as much as possible out of the ecm and forcing it to stay in open loop and if all that still fails and the stumble is still at idle just switching to a completely new management system and removing all the limitations of the factory ecm.

 

Again, I'm pretty sure your car is going into closed-loop mode. That's why it's not running right. If you could force it to stay in open-loop mode, it wouldn't run badly because it would ignore the O2 sensors.

You've clearly crossed a bad O2 sensor off the list. The only thing you haven't done that I can see is to probe the wire at the ECM while running in closed-loop mode to see if you are getting a variable voltage there vs a flatline 450mv. If you're getting a variable signal there, then either the ECM really is back, or at least the pin on the harness plug is bad.

 

Just did some more testing and found out some more info, as the car was running I back probed the ecm and as the car was running I could see voltage moving via my multi meter but still noo movement on myscanner. On another note I know that it’s stuck in open loop because I am able to view the loop status as well as a error I’m receiving is closed loop enable time over due. Meaning that the car is unable to enter closed loop due to being in open for to long.

im at the part where I decide to either to remove everything and all the parts I put into it and change my route or continue to fix what’s going on with a ecm replacement and hope everything thing else is in good condition and working order. I appreciate the help! I’ll update the post if anything changes

 

Well, that certainly does speak to the problem actually being the ECM. I don't know how easy/cheap these are buy, but another option could be SIA Electronics in Illinois. They can test and repair your ECM.

Maybe these older ECMs really work differently than the 94-96 units. I don't know why it would run badly if it's stuck in open-loop: it's clearly not ignoring the O2 sensors as it would in open-loop, or else it would continue to run okay like it does when warming up. I wonder if that's a semantic thing in the readings: like maybe it only calls it closed-loop if everything is operating properly, even though it's trying to read all the sensors? In any case, I think you've done as much diagnosis as possible. Good luck!

 

It takes three primary parts to allow your car to work in "Closed Loop".

The First is the Oxygen Sensor, always replace after 24 months or 50K miles. They wear out, they default to the "Rich" side to protect your engine. Later cars came with dual sensors on each side. The UP Stream Oxygen sensor should be bouncing back and forth very quickly where the down stream sensor has a more stable output since it is watching for Cat failure. This should be the same on the left side and the right side.

The second is the Coolant Temperature Sensor, this little bugger does wear out occasionally and simply shifts the temperature range of the unit. If the CTS tells your Computer that it is 20* where in fact it is really 80* you have real problems. The engine would run rich and eventually possibly damage the Oxygen Sensor and plug the catalytic. The same CTS could also tell your car it is 120* when you first try to start the car some winter morning, and this would make starting the engine an issue.

The Third item is the Mass Air Flow or Mass Air Pressure sensor. The sensor is supposed to measure to Volume of air being ingested by the engine. The MAF is a very precise measuring device and is mounted in the air hose connecting to the Throttle Body. There can be NO leaks at all in the tubing between the MAF and the throttle body. Any air getting in causes driving issues. The MAP sensor does the same thing but in a different way.

I read that when the ECM was faulty that it would make the cooling fans all run wide open. If your Corvette can't go into the Closed loop and is in fact stuck in closed loop it means that one of those three is not doing their job. Either put your O2's back the way they were or replace them all. Can the engine start and run okay? Using your new scanner what does it tell you?

 

Hello All - sorry to revive an old thread, but I am unable to message Livewild directly :-) I have a 1991, and am facing exactly the same issue. Code 13, light comes on when it tries to go into closed loop. Need to backprobe the O2 sensor while running to confirm the voltage, but have had the same behavior with multiple sensors (new and known good). I tested the purple wire from the ECM pin to the connector at the sensor, with 0 resistance, as I was thinking I would find an open in that circuit. With all that said, I wanted to ask if you ever got this sorted out, as it sure points to the ECM, but that doesn't feel quite right. Thank you!

 

it’s been a while not sure exactly what I did, but the the code 13 is real generic and could mean a few different things. It depends on the module your getting the code In. What I do remember is I skipped the wiring harness completely and ran a solid wire from the sensor to the ecm. Traced back a little
from plug to the ecm cut and put the wire in. I did have a moats live data reader that allowed me to see everything real time. That helped me a lot. But after dealing with that for a while I left it alone and it just fixed itself. It took my car a while to go from open to closed, like stated earlier it dose take a few other components and variables to swap modes. And as far as the misfire, that’s what I could never figure out when I had the car. Everything from coil to opti to injectors and pump and everything in-between was replaced. Once I sold the car I was helping a friend with a hot rod caprice wagon. Similar work and I noticed it still had that horrible misfire once it got warm. Looked into it and finally figured out lt1’s are know for having shotty lifter springs. Never confirmed it he sold the car as well. But that would be my next bet. No way two completely different cars had the exact same problems with similar work done. The last thing in the puzzle was the lifters Just never had a chance to change them
out

 

And after all that typing I realized I think you have the l98 which is crazy different than the lt1 92+ ecm problems. That code most likely means something completely different than what I think it is. But something I said hopefully gave you an idea of my situation. If there is any more specifics on the code and what it means im sure someone could help steer you in a right direction

 

Thanks so much for the reply Livewild! Since your symptoms with that O2 sensor circuit were so unique to mine, and about the only instance I could find on the internet, I was really hopeful to hear how yours ended up. When you ran your own wire to the ecm, did you splice on a new male connector end by chance? I had a very surprising thing happen tonight - the body side connector on my car was cracked since I bought it, so I had ordered a new one and it arrived tonight. In the interim, I had removed the plastic from the connector, and it was seated into the O2 connector just fine, terminal to terminal - code 13 and driveability issues persisted. Tonight I spliced on the new male end, got it heat shrinked up, and drove it for 20 miles. No code 13, SES, or driveability issues. I was really not expecting this, as it seemed to have been making good electrical connection with the old connector. In any regard, that seems to have resolved my issue, as it ran better tonight than it has since I bought it, and the light surging I normally had at low speeds with the clutch in was also gone.

I appreciate you taking the time to post this initially, and get back to me 3 years later - it helped me alot :-)