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Discussion Starter #1
I want to upgrade my o2 sensor to a heated sensor, as it’s in need of replacement and I feel that since I coast a lot in 5th gear or with the engine off, my sensor probably is cooling below the threshold at which it’s supposed to work. This is all based on limited research.

I understand that wiring the sensor consists of a ground (either bolting to the exhaust manifold or a separate ground wire), the signal wire (into the one wire from my factory o2 sensor), and the heater wire, which I’m not sure exactly where I’ll run that into but I’m thinking fuel pump relay or fuse?

I haven’t pulled the factory lambda off but it looks like rather than threading into the exhaust, it’s actually bolted to it. My question is this: is there a heated sensor that is compatible with this setup? If not, could I use some sort of a block off plate and weld a bung into the exhaust pre-cat? My cat is getting ready to let go, I already have a flowmaster from a previous project that wasn’t ever used. It’s got two bungs welded to it, one on either side. Is there a way to block off the post cat bung?

This forum has helped me immensely with my $280 corolla and I look forward to being a part of it for quite some time. Thanks in advance for helping with this matter.




TL;DR: I want to wire in a heated o2 sensor and I’m looking for fitment options
 

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1992 Geo Prizm
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If it uses a bolt on style o2 sensor, you'd have to look for one. Try Denso's web site, as they have a lot of o2 sensors for different applications, and it might narrow your choices. As for blocking that spot and moving it, that could work too, but you'll need to keep it as close to the exhaust manifold as you can, because moving it further back will allow it to cool (even if heated), and cause a rich condition. Flow master and other companies make screw in plugs for o2 bungs, so you might want to check with your local auto parts places first, and maybe even e-bay.


As for wiring in a heated O2 sensor, you'll have 2 grounds (1 for the o2 sensor, and 1 for the heated portion) then you'll have a signal wire (goes to the ECM) and 1 wire to a 12 volt with key on wire. Hense your 4 wires to a heated O2.
 

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Heater on O2-sensor is still ECM controlled with PWM signal to maintain constant temperature (ratio of exhaust + heater). As car and exhaust warms up, ECM dials back on heater to maintain same temperature. You'll need ECM that has code to control O2-sensor heater.
 

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1997 Corolla
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I'm not sure if you'll gain much by installing a heated O2 sensor. I don't think it would cool appreciably even with the engine off for a few minutes. The 7th gens don't have a heated sensor on the front either. The rear O2 sensor on 7th gens is heated, but that sensor is only used to monitor the catalytic converter for emission regulations. Maybe newer cars all have heated sensors all around.

As for wiring in a heated O2 sensor, you'll have 2 grounds (1 for the o2 sensor, and 1 for the heated portion) then you'll have a signal wire (goes to the ECM) and 1 wire to a 12 volt with key on wire. Hense your 4 wires to a heated O2.
The sensor part signal wire is positive and the other wire is grounded to the computer ground (E1) like the other sensors. Like DannoXYZ said the heater is controlled by the ECU, and the heater has a +B connection and is grounded by/at the ECU. +B comes from the EFI fuse and EFI relay. If the heater were on all the time it might fail earlier, and how would you know if it failed anyway if not connected to ECU? (If it failed open-circuit.) ECUs that control the O2 sensor heater will throw a code if the heater fails.
 

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Discussion Starter #5
Longer shot, would there be an available wideband sensor that fits the factory location so I could monitor my afr? That'd help with carb tuning when I swap for a weber I think. Or would I be better off just replacing the factory with another and putting a wideband downstream of it? I just know I'm gonna be tearing into it soon and would like to improve while I'm down there. I'm also planning on putting a header on pretty soon and don't want to buy a factory sensor if it can be avoided.
 

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Don’t put wideband at stock location, that’s too close and too hot and will harm wideband sensor. Put factory sensor in factory location. Wideband should be 20-24” from beginning of header.
 

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Heater on O2-sensor is still ECM controlled with PWM signal to maintain constant temperature (ratio of exhaust + heater). As car and exhaust warms up, ECM dials back on heater to maintain same temperature. You'll need ECM that has code to control O2-sensor heater.
Why is it that the GM guys just add a couple of wires to run a heated O2 sensor in place of the single wire unit? When the heated version is used, you get a finer/better reading (leaner?) than the 1 wire unit. That's also with only using the single wire O2 sensor ECM too (power supplied for the heater comes from the fuse box).
 

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Discussion Starter #9
Why is it that the GM guys just add a couple of wires to run a heated O2 sensor in place of the single wire unit? When the heated version is used, you get a finer/better reading (leaner?) than the 1 wire unit. That's also with only using the single wire O2 sensor ECM too (power supplied for the heater comes from the fuse box).
I was actually reading a bunch of stuff about GM guys doing it, which is partially what brought me to want to do the same thing on my '88 corolla
 

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Why is it that the GM guys just add a couple of wires to run a heated O2 sensor in place of the single wire unit? When the heated version is used, you get a finer/better reading (leaner?) than the 1 wire unit. That's also with only using the single wire O2 sensor ECM too (power supplied for the heater comes from the fuse box).
You do realize you're talking about a company that went bankrupt because they have such crappy products right? There's absolutely difference in meals you get from S.F.'s Laurel Court restaurant versus any Burger King. Toyota uses ECM-controlled heated O2-sensor so constant-temperature can be maintained. When engine's cold, when you're flooring it, when cruising on freeway all require different contribution from heater.

Proper double-blind testing is also needed. In GM example, exact same brand-new O2-sensor must be used. With and without heater turned on. Comparing two different sensor of different types and ages yields invalid data for comparison due to extra variables. You'd also need to use exact same wideband O2-sensor as control to verify actual AFR between those two tests. And it must be something other than LM-1 because that unit uses analogue gauge without regulated reference voltage. Exact same AFR displayed would vary depending upon state of battery charge and whether you had headlights turned on or off.

First, if the O2-sensor actually needed a heater, then some engineer messed up. O2-sensor was placed too far from exhaust valves. Not on Toyotas, they did it perfectly. Primary 1-wire O2-sensor close to exhaust-valves and secondary 4-wire heated O2-sensor further downstream. Only 2nd/downstream O2-sensor needed heater because it was placed 3-feet from exhaust-valve and needed its own heat supply.

Second, IF you replaced Toyota's primary O2-sensor with heated one, there will be absolutely zero difference in readings because non-heated one will put out exact same signal as heated O2-sensor due to optimum placement. Retrofitting car with more modern ECM to run heated O2-sensor will yield no difference in exhaust readings and no difference in performance or MPG.

Although some newer OBD-II cars DO come with heated primary O2-sensor, but that's purely for quicker transition to closed-loop operation and lower-emissions. Again, nothing to do with accuracy or performance and specific ECU + matching heated O2-sensor needed.

Have you even looked at O2-sensor signal on your car with oscilloscope? How would you even know if signal is not accurate?

 

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1991 Toyota Corolla
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Hey feardamichael,

Just read your post and figured I could potentially give you some late insight. I have a Corolla with the 4afe engine. I installed the pacesetter exhaust manifold. A few months later, I needed to replace my oxygen sensor. I tried two aftermarket sensors and one of those was a denso (oem). The issue I ran into was the bung was too small in diameter to fit either of the oxygen sensors I purchased although both of those sensors would fit in the factory exhaust perfectly fine. I didn't want to ditch the pacesetter manifold. I went to Napa and was able to purchase a toyota 2 bolt flange adapter. Now, I was able to screw in any oxygen sensor in its place. I picked one out at my local Carquest that was a bit thinner in diameter from the factory sensor. The one I purchased was a 4 wire sensor. I removed the 2 heater wires and ran it as a 2 wire sensor. Car runs great now. Hopefully this helps in some way.
 
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