LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Serious closed loop problem please help!

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Old Jun 25, 2004 | 11:49 PM
  #16  
JTS95TA's Avatar
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From: Lake Zurich IL
Well the car will run great when I unplug the 02's, but how do I get the readings from them if they are disconnected? or do you mean find out what the computer puts it at with no 02's connected?

Thanks
Old Jun 25, 2004 | 11:53 PM
  #17  
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yep

that was a good idea dave. with the sensors unplugged, the scanner should read around 450mv steady. this will test the wires to the pcm.
Old Jun 26, 2004 | 12:20 AM
  #18  
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Ok so if I unplug the 02's the computer should default to .450mv? and when you say this will test the wiring to the PCM, is that because it will show that now the computer recognizes nothing connected to it anymore proving the wires are actually doing something?

Wow this problem really has me stumbled now.

Last edited by JTS95TA; Jun 26, 2004 at 12:26 AM.
Old Jun 26, 2004 | 12:32 AM
  #19  
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the pcm does not go default. that is just the voltage that it should read with the 02 unplugged. in other words, the pcm gives the 02s 450mv to play with. the 02 is supposed to toggle the 450mv up and down.

if the pcm does not go 450, or close to 450 then there might be a wiring problem or faulty pcm.

if you do achieve 450mv with sensor unplugged then your wiring and pcm are fine. then you will know that either the 02 sensor or header or exhaust leak are to blame.

you might not get 450mv right away with the ignition on. it may take a few minutes but it should be around that area with no 02 connected.
Old Jun 28, 2004 | 07:21 PM
  #20  
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Ok I have an update for everyone. As I said before I repaired all my 02 wiring. Today I bought new 02 sensors and put them in. I then drove the car and so far all day today it has been running pretty good surprisingly. However the last time I bought new 02's it did the same thing ran good for a couple days then finally took a crap. As of right now the car does go into closed loop and runs good. I also ran the laptop and the 02's are doing what they should fluctuating back and forth throughout the range. At WOT they are sitting a bit rich at around mid .950mv's sometimes higher but I figures thats because I have longtubes. I am still not 100% convinced the problem is fixed I figure in a day or two it will take a crap on me again. Now this brings up another question, if it does infact get bad again what is causing the 02's to die like this? It must be something in the exhaust stream. A friend mentioned a possible slightly blown headgasket and coolant is killing the 02's after a couple days. This makes perfect sense, but I have never added a drop of coolant to my car since I have owned it for two years and its always topped off. Any other ideas would could possibly be killing the 02's?
thanks again for the help
James
Old Jun 29, 2004 | 02:54 PM
  #21  
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Check your IAC, I know it sounds weird but I had the same problem as you and this past weekend I changed my intake gasket cleaned my IAC and switched my injectors from left to right. I also changed my O2 Sensors around. It runs a lot better now and the IAC was really dirty. My passenger side was reading 10 MV at times making my cylinders missfire.
I think either the intake leak (vaccuum leak maybe) or the IAC may have fixed it. I guess if the computer sees a bunch of extra air from the intake leak, it is gonna try and compensate with a bunch of fuel causing the car to run and smell really rich. (at least mine was). Maybe the extra unburned fuel in the exhaust gasses will kill the O2 sensor?
Good luck and keep us posted. I would hate it if mine started running like crap again.
Check out my post HERE
Old Jul 6, 2004 | 08:52 PM
  #22  
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let me know how replacing the O2's is going. I am having the same problem you had and it's driving me crazy.
Old Jul 6, 2004 | 09:18 PM
  #23  
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Well suprisingly the car is still running pretty good in closed loop now. Its been since June 28 and I have drivin the car everyday since then and it has not givin me any problems yet. For some reason The car still seems a little shaky as the rpms go up, but it isnt a big deal it idles good and cruises fine. Im still not 100% sure its gonna keep running this good but so far it looks pretty promising since it has been over a week. I still dont know exactly what the problem was. The last thing I did before I changed the 02's this time was replace and re-solder all my 02 sensor wiring. Who knows if it takes a crap on me again I will post it. And if that happens im gonna sell the car.
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