O2 sensor bad?
07-28-2010, 08:12 PM
#1
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Location: KS, USA
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O2 sensor bad?
94 Z28, 113K miles, LT1 - auto, K&N CAI, Hooker long tubes, PI converter (2800), 3.73 gears, newer opti-spark - waterpump, newer plugs & wires, newer ICM.
I have a slight hesitation/miss that seems to come around after warmup and the car is in closed loop. It is only noticable under light to moderate load. WOT I don't seem to notice anything (other than some black smoke). It is running rich as evidenced by the smoke and carbon build up on the tailpipes. I only got 13mpg last tank of gas and that was highway mostly! Some readings from the scanmaster are as follows: LIN/RIN = 120-130/180-190, LBL/RBL = 120ish/160ish, LO2/RO2 = 449/normal up and down movement. This was all read at cruising speeds of 70mph. It seems the LO2 wants to "stick" at 449 but will jump around periodically. I am not sure how old the O2 sensors are, they were on there along with the longtubes, when I bought the car at 98,000 miles. So my question is whether or not the O2's are shot? Any help from the knowledgable people on this board would be much appreciated!
I have a slight hesitation/miss that seems to come around after warmup and the car is in closed loop. It is only noticable under light to moderate load. WOT I don't seem to notice anything (other than some black smoke). It is running rich as evidenced by the smoke and carbon build up on the tailpipes. I only got 13mpg last tank of gas and that was highway mostly! Some readings from the scanmaster are as follows: LIN/RIN = 120-130/180-190, LBL/RBL = 120ish/160ish, LO2/RO2 = 449/normal up and down movement. This was all read at cruising speeds of 70mph. It seems the LO2 wants to "stick" at 449 but will jump around periodically. I am not sure how old the O2 sensors are, they were on there along with the longtubes, when I bought the car at 98,000 miles. So my question is whether or not the O2's are shot? Any help from the knowledgable people on this board would be much appreciated!
07-29-2010, 06:34 AM
#2
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If your sensors are staying at ~.45v then they aren't connected, warmed up, or are dead. If a sensor isn't cycling (or stops cycling), the PCM will revert to open loop control as the perceived o2 status is "not ready". If the sensors are cycling within a couple minutes of cold startup, then they are usually fine.
I wonder if the 'sticking' is simply due to a slow sample rate (or averaging) of the scanmaster.
I wonder if the 'sticking' is simply due to a slow sample rate (or averaging) of the scanmaster.
07-29-2010, 06:45 AM
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Location: Kissimmee, Fl, USA
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I assume you don't have a SES light...correct?
Since headers are involved, look for an upstream exhaust leak..that will make it run rich.
I've seen weird responses from non-GM O2 sensors after they age so it might well be the sensors since you don't know the age or brand. To be clear, the wierd responses I've seen weren't on an LT1...it was an LS6 with NTK (NGK) sensors. They are a 'wear' item like plugs, wires, and distributor caps and have a finite life...
Since headers are involved, look for an upstream exhaust leak..that will make it run rich.
I've seen weird responses from non-GM O2 sensors after they age so it might well be the sensors since you don't know the age or brand. To be clear, the wierd responses I've seen weren't on an LT1...it was an LS6 with NTK (NGK) sensors. They are a 'wear' item like plugs, wires, and distributor caps and have a finite life...
07-29-2010, 08:55 AM
#4
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Join Date: Apr 1999
Location: KS, USA
Posts: 68
If your sensors are staying at ~.45v then they aren't connected, warmed up, or are dead. If a sensor isn't cycling (or stops cycling), the PCM will revert to open loop control as the perceived o2 status is "not ready". If the sensors are cycling within a couple minutes of cold startup, then they are usually fine.
I wonder if the 'sticking' is simply due to a slow sample rate (or averaging) of the scanmaster.
I wonder if the 'sticking' is simply due to a slow sample rate (or averaging) of the scanmaster.
I assume you don't have a SES light...correct?
Since headers are involved, look for an upstream exhaust leak..that will make it run rich.
I've seen weird responses from non-GM O2 sensors after they age so it might well be the sensors since you don't know the age or brand. To be clear, the wierd responses I've seen weren't on an LT1...it was an LS6 with NTK (NGK) sensors. They are a 'wear' item like plugs, wires, and distributor caps and have a finite life...
Since headers are involved, look for an upstream exhaust leak..that will make it run rich.
I've seen weird responses from non-GM O2 sensors after they age so it might well be the sensors since you don't know the age or brand. To be clear, the wierd responses I've seen weren't on an LT1...it was an LS6 with NTK (NGK) sensors. They are a 'wear' item like plugs, wires, and distributor caps and have a finite life...
07-29-2010, 12:48 PM
#5
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Sounds like there's more to it than that.
The driver's side (left) O2 circuit probably has an intermittent connection. Reads ~450mV when its disconnected, than starts to function normally when the connection is temporarily re-established. The loose bolts on the driver's side manifold should have caused elevated long term fuel corrections (BLM's), but if they are "120ish" they aren't elevated.
Then there's the passenger side (right). With a 160 BLM, its adding 25% extra fuel. The 180-190 INT is adding 45% extra fuel. Since the terms are multiplied by each other, its adding 80% more fuel than the PCM thinks it should add. You really need to figure out if that is a "true" lean condition that is being corrected, or a "false" lean condition. If its a false lean, the oil is probably full of gasoline by now. The plugs should be totally carboned up .
So far, I don't think you've figured it out at all.
The driver's side (left) O2 circuit probably has an intermittent connection. Reads ~450mV when its disconnected, than starts to function normally when the connection is temporarily re-established. The loose bolts on the driver's side manifold should have caused elevated long term fuel corrections (BLM's), but if they are "120ish" they aren't elevated.
Then there's the passenger side (right). With a 160 BLM, its adding 25% extra fuel. The 180-190 INT is adding 45% extra fuel. Since the terms are multiplied by each other, its adding 80% more fuel than the PCM thinks it should add. You really need to figure out if that is a "true" lean condition that is being corrected, or a "false" lean condition. If its a false lean, the oil is probably full of gasoline by now. The plugs should be totally carboned up .
So far, I don't think you've figured it out at all.
07-29-2010, 10:07 PM
#6
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Join Date: Apr 1999
Location: KS, USA
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Sounds like there's more to it than that.
The driver's side (left) O2 circuit probably has an intermittent connection. Reads ~450mV when its disconnected, than starts to function normally when the connection is temporarily re-established. The loose bolts on the driver's side manifold should have caused elevated long term fuel corrections (BLM's), but if they are "120ish" they aren't elevated.
Then there's the passenger side (right). With a 160 BLM, its adding 25% extra fuel. The 180-190 INT is adding 45% extra fuel. Since the terms are multiplied by each other, its adding 80% more fuel than the PCM thinks it should add. You really need to figure out if that is a "true" lean condition that is being corrected, or a "false" lean condition. If its a false lean, the oil is probably full of gasoline by now. The plugs should be totally carboned up .
So far, I don't think you've figured it out at all.
The driver's side (left) O2 circuit probably has an intermittent connection. Reads ~450mV when its disconnected, than starts to function normally when the connection is temporarily re-established. The loose bolts on the driver's side manifold should have caused elevated long term fuel corrections (BLM's), but if they are "120ish" they aren't elevated.
Then there's the passenger side (right). With a 160 BLM, its adding 25% extra fuel. The 180-190 INT is adding 45% extra fuel. Since the terms are multiplied by each other, its adding 80% more fuel than the PCM thinks it should add. You really need to figure out if that is a "true" lean condition that is being corrected, or a "false" lean condition. If its a false lean, the oil is probably full of gasoline by now. The plugs should be totally carboned up .
So far, I don't think you've figured it out at all.
The RBL seemed to stay at 160 today while the LBL was at 120. The RIN was reading around 140-150 and LIN 120-130.
The oil was fairly fresh according to the previous owner but when I checked it, it looked pretty black (used up). The extra fuel being dumped in (if that is the case) could have caused this, correct? I did pull the cylinder 1 plug and it didn't look bad. I guess I need to pull a few plugs on the pass side.... The car only got about 8,000 miles put on it over 7 years so I don't think all the sitting around did it any good!
08-02-2010, 09:19 AM
#7
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Join Date: Apr 1999
Location: KS, USA
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Update: Looks like I was on the right track.... I think the rich condition started out as a header exhaust leak and kinda snowballed from there. Everything I saw pointed to bad 02 sensors (the right one was completely clogged with carbon build-up) so i installed new acdelco ones and problem fixed! Thanks for your help/info guys!
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