O2 sensor

[STEBS]

been doin some reading up and studying for my ASE, and a question came to mind...

on the 87-95 tbi, it utilizes 2 o2 sensors, 1 at the driver side exhaust manifold, and the other at the y pipe...neither of wich are after the cat, i know gm probly spent countless hrs of research back in 86 to come up with the tbi fuel injection... but i got to wonder, how efficient is this design?

if i were to move the 02 sensors, 1st at the y pipe (so to read both manifold exhaust readings rather than just 1) and the other post cat... in theory should i see better fuel milage, and better throttle response?

 

[X-Cutioner]

i have a 95 k1500 and it only has the 1 in the y-pipe
i diffinently know there is only one becuase i pulled the computer pin-out wiring schematic so i knew which wire to tap for my o2 graph

i know that a 92 had it in the driver manifold

 

[jeff's88silverado]

all the TBI's i can think of only had 1 o2 sensor

 

[Aloicious]

no, I don't see where you'd get increased mileage and throttle response by installing a post cat sensor...the pre cat sensors are used for fueling trims, the post cat sensors are typically used to verify cat efficiency.

I'm not sure on the TBI O2 sensor installation variations, but if you've got 2 sensors, one on the drivers side bank, and the other in the Y pipe pre-cat. then they are both going to be used for fueling trims. having separate bank O2 sensors is very beneficial on port injection because the fuel can differ from bank to bank, and hence the trims are used to curb those variations. where in TBI and carb, the fuel is introduced all together and theoretically should be a uniform mixture by the time it reaches the cylinder. so individual bank O2 sensors would just be added cost for redundancy. most likely the reasoning behind the placements you mention are for the most upstream sensor will be used for trims, and likely the one in the Y pipe would be a verification sensor since that is where all the exhaust gas is present.

I thought the TBI's had 1 pre and 1 post cat sensor, but I could be wrong. in any case the post cat sensors job (in typical setups) is simply to monitor the exhaust after it passes through the cat to ensure the cat is functioning correctly. it typically doesn't make fueling corrections, or anything that would directly affect fuel mileage or throttle response....UNLESS you have bad cats, and the O2 sensor was seeing that, then the only gain you'd get would be from replacing the bad cats.....besides, if the ECM for the TBI's isn't programmed to have a post cat O2 sensor, you wouldn't be able to add one directly to the engine control module, it simply wouldn't know what to do with the data it recieved, then you're getting into ECM/PCM swaps, programming and chip burning, etc....all for a post cat O2 sensor, which wouldn't really give you any benefit other than being able to illuminate the SES light when you get a bad cat.

 

[Aloicious]

also, forgot to mention, that moving the primary O2 sensor back to the Y pipe isn't a good idea either, since the further downstream you move them, the more error they produce (since the exhaust has to travel further before it reaches the sensor) and the more inaccurate the trims will be...

 

[STEBS]

no, I don't see where you'd get increased mileage and throttle response by installing a post cat sensor...the pre cat sensors are used for fueling trims, the post cat sensors are typically used to verify cat efficiency.

I'm not sure on the TBI O2 sensor installation variations, but if you've got 2 sensors, one on the drivers side bank, and the other in the Y pipe pre-cat. then they are both going to be used for fueling trims. having separate bank O2 sensors is very beneficial on port injection because the fuel can differ from bank to bank, and hence the trims are used to curb those variations. where in TBI and carb, the fuel is introduced all together and theoretically should be a uniform mixture by the time it reaches the cylinder. so individual bank O2 sensors would just be added cost for redundancy. most likely the reasoning behind the placements you mention are for the most upstream sensor will be used for trims, and likely the one in the Y pipe would be a verification sensor since that is where all the exhaust gas is present.

I thought the TBI's had 1 pre and 1 post cat sensor, but I could be wrong. in any case the post cat sensors job (in typical setups) is simply to monitor the exhaust after it passes through the cat to ensure the cat is functioning correctly. it typically doesn't make fueling corrections, or anything that would directly affect fuel mileage or throttle response....UNLESS you have bad cats, and the O2 sensor was seeing that, then the only gain you'd get would be from replacing the bad cats.....besides, if the ECM for the TBI's isn't programmed to have a post cat O2 sensor, you wouldn't be able to add one directly to the engine control module, it simply wouldn't know what to do with the data it recieved, then you're getting into ECM/PCM swaps, programming and chip burning, etc....all for a post cat O2 sensor, which wouldn't really give you any benefit other than being able to illuminate the SES light when you get a bad cat.

now, that u put it that way, gm's design makes a lil more sence, and im not afraid to admit that while reading ur post, i kinda had a "duh" moment when i thought about my initial question... i guess i was just overthinking it a lil too much

but to add to previous posts about o2 location, idk if its just the v6, or just 92, or wat designation called for it, but my 92 does have 2... i guess i just kinda assumed that the rest of the tbi's were simular

 

[Aloicious]

now, that u put it that way, gm's design makes a lil more sence, and im not afraid to admit that while reading ur post, i kinda had a "duh" moment when i thought about my initial question... i guess i was just overthinking it a lil too much

but to add to previous posts about o2 location, idk if its just the v6, or just 92, or wat designation called for it, but my 92 does have 2... i guess i just kinda assumed that the rest of the tbi's were simular

no worries, it happens...overthinking isn't a bad thing...it's acting without research or testing that proves problematic most of the time...

 

[STEBS]

i try as much research and as many 2nd opinions as i can get before i do lol

 

[97PROSHOZ71]

I wish the O2 sensors weren't so picky, I've had a bad one forever, throws my check engine light on, occasionally it goes off depending on how the weather is, noticeable difference in power and mileage when that light is off.

 

[Aloicious]

the difference in mileage and power is because they are changing the fueling of the engine...they also wear out over time. its a smart idea to replace them as a part of regular maintenence...not necissarily overly frequently like oil or something, but y'know, every 50-100k wouldn't hurt....

I've been thinking for a while of pulishing an article on O2 sensors, how they work, etc...after I get done will the current things I'm working on I might have to do that, I think it'd be fairly helpful especially since there seems to be some misunderstanding about them (not judging from this thread, or the OP or anything, just in general)