2000 Trans Am running in Open Loop only
#1
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I bought a 2000 Trans Am a few weeks ago and it had been worked on by a pretty shoddy mechanic. I have been going through fixing the messed up stuff that was done to it. The previous owner had Texas Speed shorty headers installed with a Corsa catback. It previously had cats and both sets of O2 sensors installed from what I can gather. The car is running in open loop only and is running pretty rich. I hooked up HP Tuners to it just to look at some things and it runs better when you manually command closed loop. So I started doing some digging around and it brought me to the O2 sensors. I am getting fluctuating readings from both sets of O2 sensors even though it looks like only one pair is installed. I'm confused on how that can be. Before I get crazy tearing things apart I was hoping for some advice on what to do next from people with way more experience than me on this.
#2
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So upon further inspection there is a rectangular box that is about a half inch wide by 2 1/2 inches long that has a pigtail that looks to be plugged into the secondary O2 connector. There is one on each one of them.
Edit: It looks like those are O2 sensor simulators of some sort. I unplugged both of them and the voltage goes to .445 on each one indicating it is unplugged.
Edit: It looks like those are O2 sensor simulators of some sort. I unplugged both of them and the voltage goes to .445 on each one indicating it is unplugged.
Last edited by GPHusker; 08-24-2020 at 09:23 AM.
#3
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I'm no expert, but I know that the rear O2's don't have any actual effect on engine performance, they just exist to throw a light if there's a problem with the cat. Given the shoddy mechanical work you've seen so far, I should mention that the exhaust shop that installed my long tube headers put the rear O2's in place of the front O2's, and I couldn't figure out why my car was running like garbage and stuck in open loop. When I picked up my car they said they "didn't need" the extensions I provided, and I was like "Huh. Okay." Well once I figured out why, I made them fix it for free and use the extensions I had originally bought on the ACTUAL front O2's. (It was either that or I had to get the Corvette O2s to reach.)
The simulators are for passing inspection right? But I wonder if they mixed up the 4 sensors like my shop did the first time.
By the way, it's also possible your front O2's are just .. bad. But I don't want to suggest just throwing money at it, someone else with more experience and knowledge might be able to help better. You're not getting any O2 low voltage codes from the front ones (Bank 1 x Sensor 1, and Bank 2 x Sensor1 I believe) are you? My long tube headers destroyed my factory front O2 sensors pretty fast, and I had to replace them.
The simulators are for passing inspection right? But I wonder if they mixed up the 4 sensors like my shop did the first time.
By the way, it's also possible your front O2's are just .. bad. But I don't want to suggest just throwing money at it, someone else with more experience and knowledge might be able to help better. You're not getting any O2 low voltage codes from the front ones (Bank 1 x Sensor 1, and Bank 2 x Sensor1 I believe) are you? My long tube headers destroyed my factory front O2 sensors pretty fast, and I had to replace them.
Last edited by SouthernRex; 08-25-2020 at 10:55 PM.
#4
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I'm no expert, but I know that the rear O2's don't have any actual effect on engine performance, they just exist to throw a light if there's a problem with the cat. Given the shoddy mechanical work you've seen so far, I should mention that the exhaust shop that installed my long tube headers put the rear O2's in place of the front O2's, and I couldn't figure out why my car was running like garbage and stuck in open loop. When I picked up my car they said they "didn't need" the extensions I provided, and I was like "Huh. Okay." Well once I figured out why, I made them fix it for free and use the extensions I had originally bought on the ACTUAL front O2's. (It was either that or I had to get the Corvette O2s to reach.)
The simulators are for passing inspection right? But I wonder if they mixed up the 4 sensors like my shop did the first time.
By the way, it's also possible your front O2's are just .. bad. But I don't want to suggest just throwing money at it, someone else with more experience and knowledge might be able to help better. You're not getting any O2 low voltage codes from the front ones (Bank 1 x Sensor 1, and Bank 2 x Sensor1 I believe) are you? My long tube headers destroyed my factory front O2 sensors pretty fast, and I had to replace them.
The simulators are for passing inspection right? But I wonder if they mixed up the 4 sensors like my shop did the first time.
By the way, it's also possible your front O2's are just .. bad. But I don't want to suggest just throwing money at it, someone else with more experience and knowledge might be able to help better. You're not getting any O2 low voltage codes from the front ones (Bank 1 x Sensor 1, and Bank 2 x Sensor1 I believe) are you? My long tube headers destroyed my factory front O2 sensors pretty fast, and I had to replace them.
#5
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You can run full-time open loop if the car is properly tuned for it; I've done it for years at a time. You don't need O2's at all in that case. MAF, VE, and AFR tables have all to be in the ball park. If so, you shouldn't see a decrease in fuel economy. Since there is no feedback, fuel trimming is turned off as you found.