O2 sensor disconnected
Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
"The oxygen sensor in your Corvette is an important, if not vitally necessary, component of your vehicle's exhaust system. The oxygen sensor detects the quantity of oxygen present in the exhaust and communicates with the exhaust system so that the engine can regulate the fuel/air mixture in order to properly and most efficiently operate.
If your oxygen sensor is broken or otherwise malfunctioning, you may need to repair it or replace it before you can ensure that your vehicle is operating at the proper fuel and air mixture. Failing to act quickly enough can result in permanent and costly damage to your vehicle's exhaust system. So read below to learn how to find and repair your broken oxygen sensor."
Copied from this link: https://www.corvetteforum.com/articl...iyoverview.php
If your oxygen sensor is broken or otherwise malfunctioning, you may need to repair it or replace it before you can ensure that your vehicle is operating at the proper fuel and air mixture. Failing to act quickly enough can result in permanent and costly damage to your vehicle's exhaust system. So read below to learn how to find and repair your broken oxygen sensor."
Copied from this link: https://www.corvetteforum.com/articl...iyoverview.php
Thread Starter
Drifting
Joined: Oct 2001
Posts: 1,444
Likes: 4
From: Hawthorne NJ
Actually, my sensor was not broken, the wire was disconnected.
The reason why I asked in a rather vague way is because the car overheated for no apparent reason and I wondered if the two things were at all related. Car is now apart for other work and that's when I noticed the o2 wire. Can't run it for a while, and just wondered if I had found a cause for the overheating.
Thanks
The reason why I asked in a rather vague way is because the car overheated for no apparent reason and I wondered if the two things were at all related. Car is now apart for other work and that's when I noticed the o2 wire. Can't run it for a while, and just wondered if I had found a cause for the overheating.
Thanks
Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
Lack of coolant flow...... faulty pump or faulty t-stat, or insufficient coolant in system.
Lack of air flow...... fans not activating as programmed, debris behind radiator blocking air flow.
Worse case condition.... head gasket rupture.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
The engine goes into limp home mode if the O2 sensor is disconnected. The engine runs on a pre-programmed set of parameters and the mixture is enriched to assist in internal fuel cooling.
Your gas mileage would have gone down maybe 8-10 mpg average if it was disconnected that long.
If the thing overheated, check for the trash accumulation, low coolant, the radiator cap no good, thermostat stuck, fan not coming on, the overflow bottle getting fuller every day, blown head gasket, hose leakage, heater core leakage, vacuum leaks, etc.
These things run around 200 in the summer. 215 in traffic in the summer.
Your gas mileage would have gone down maybe 8-10 mpg average if it was disconnected that long.
If the thing overheated, check for the trash accumulation, low coolant, the radiator cap no good, thermostat stuck, fan not coming on, the overflow bottle getting fuller every day, blown head gasket, hose leakage, heater core leakage, vacuum leaks, etc.
These things run around 200 in the summer. 215 in traffic in the summer.
Last edited by coupeguy2001; Jun 9, 2013 at 09:24 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The ECM might be running the engine lean, which would result in it running hotter than normal.
How did reconnecting the O2 sensor affect the way the engine runs?
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 411
From: WV
Cliff, this is the same thing I told him in his other post on this same subject....WWCorvette Stories
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Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
If your overheating was caused by a failed tstat, now would be a good time to drain the block by removing the knock sensor and tstat. Even if the tstat was not the problem, it will be inexpensive preventive maintenance.
With the tstat and knock sensor removed, flushing the block is an easy task.
Replacing both coolant sensors (analog & digital) would be
recommended, also.
With the tstat and knock sensor removed, flushing the block is an easy task.
Replacing both coolant sensors (analog & digital) would be
recommended, also.
Thread Starter
Drifting
Joined: Oct 2001
Posts: 1,444
Likes: 4
From: Hawthorne NJ
If your overheating was caused by a failed tstat, now would be a good time to drain the block by removing the knock sensor and tstat. Even if the tstat was not the problem, it will be inexpensive preventive maintenance.
With the tstat and knock sensor removed, flushing the block is an easy task.
Replacing both coolant sensors (analog & digital) would be
recommended, also.
With the tstat and knock sensor removed, flushing the block is an easy task.
Replacing both coolant sensors (analog & digital) would be
recommended, also.
Safety Car
Joined: Aug 2002
Posts: 3,842
Likes: 230
From: SANTA CRUZ CA
No, not necessary now since you have replaced the tstat. Was only suggesting that if you hadn't replaced the tstat, now would be the time to drain and flush the block. Removing the knock sensor really helps to completely drain the block.
My suggestion was only related to your heating problem, but replacing the tstat may have solved that problem. Flushing the block is just maintenance.
My suggestion was only related to your heating problem, but replacing the tstat may have solved that problem. Flushing the block is just maintenance.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
I mentioned earlier that the engine would go into limp home mode without the oxygen sensor input. I still believe that. But it has to get into the closed loop condition to get there. If the oxygen sensor wire is disconnected, it will never get out of open loop.
In limp home, the computer reverts to a preprogrammed set of parameters and richens the engine to avert damage.
When the engine is cold, and is in open loop, the computer monitors the oxygen sensor output, and watches for the 450 millivolts and then the computer checks the time that expired since the engine started, and if the millivolts and time are correct, the engine goes into closed loop, and leans out the engine according to the oxygen sensor, throttle position, and temperature of the engine.
If the oxygen sensor is not present electrically, the engine stays in the open loop condition, and delivers a rich mixture to prevent internal engine damage.
check the other things I mentioned in my previous post.
In limp home, the computer reverts to a preprogrammed set of parameters and richens the engine to avert damage.
When the engine is cold, and is in open loop, the computer monitors the oxygen sensor output, and watches for the 450 millivolts and then the computer checks the time that expired since the engine started, and if the millivolts and time are correct, the engine goes into closed loop, and leans out the engine according to the oxygen sensor, throttle position, and temperature of the engine.
If the oxygen sensor is not present electrically, the engine stays in the open loop condition, and delivers a rich mixture to prevent internal engine damage.
check the other things I mentioned in my previous post.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
I looked at the ECM schematic (1227165 -- used in '86 - '89). The output of the O2 sensor goes to a differential amplifier that has floating inputs. From there it goes to a A/D (Analog to Digital) converter and then to the microcontroller. If the O2 sensor input was open the input voltage would be zero and that's what the microcontroller would see. It would wait forever for the output to go over 450 mV and would stay in open loop mode.
One of the mysteries of the ECM for me is how it goes into LIMP mode. It appears to me that the FMD (Fuel Modeling Device) pulls the LIMP signal low, which disables the microcontroller. That seems more likely than the microcontroller pulling the LIMP signal low to put the FMD in LIMP mode because I don't see any code in the firmware that controls the LIMP signal.
I would love to have someone clarify this for me. For reference, see these links:
http://home.earthlink.net/~cliff_har...chematics.html
http://home.earthlink.net/~cliff_har...5/BUA/BUA.html
One of the mysteries of the ECM for me is how it goes into LIMP mode. It appears to me that the FMD (Fuel Modeling Device) pulls the LIMP signal low, which disables the microcontroller. That seems more likely than the microcontroller pulling the LIMP signal low to put the FMD in LIMP mode because I don't see any code in the firmware that controls the LIMP signal.
I would love to have someone clarify this for me. For reference, see these links:
http://home.earthlink.net/~cliff_har...chematics.html
http://home.earthlink.net/~cliff_har...5/BUA/BUA.html