85irocz87

hello everyone, i have a 1985 silver metallic iroc. two days ago i had about $1800.00 worth of mechanical work done. new fuel pump, water pump , brakes and so on. my mechanic said while he was working under the hood he found that the previous owner disconnected the O2 sensor, so he reconnected it. driving home from his shop the car ran like crap. it had good throttle response but everytime i stopped or slowed down it felt like it was going to stall out. when i called him he suggested maybe that was why the O2 sensor was disconnected. would the O2 sensor be the reason for this problem? basically the whole fuel system is brand new now and when i drove the car out of my garage and on to the flatbed to get it there it drove much better and at that time the O2 sensor was disconnected. is there anyway for me to check this without having to pay him with my other kidney ? Can i disconnect the O2 sensor myself and see how it drives? If so, can someone tell me exactly where the O2 sensor is located?

five7kid

iTrader: (14)

Disconnecting the O2 sensor will cause the ECM to command full-rich mode. Not good.

Need more details about what your car is/has. It is either carb or TPI. Further help will requiring knowing which it is.

The SES light should be coming on (assuming it isn't burnt out). Have you checked the computer for error codes? The O2 having been disconnected should have set one - after checking the current codes, you can clear old codes by disconnecting the ECM power for a minute, then reconnecting and starting the car and driving it again to see if any new ones are set.

Schrade

On a properly tuned motor, the O2's really don't do much more than go along for the ride...

No SES light? Is this a stock-configured motor?

Tuned Performance

iTrader: (92)

Un hook the o2 and hook up a vom, with the engine above 146F assuming the o2 is still in the exhaust manifold you can watch the o2 swing if its steady at 450mv it is bad.

Schrade

Looks like by the 'I don't understand smiley', that you don't understand.



Maybe Ray B can explain it better:






In other words, if you can LOSE it, and it has no impact ... , then it's a safe assumption that if working, and the motor is properly tuned, then for the most part, it's just going along for the ride.

Hope this clarifies your mis-understanding.

Knowledgebase OUT!

ed.:
Got the rest of the article if there's interest. I love sharing knowledge!

Also note that Ray says, Above certain throttle opening %, ECM IGNORES O2's' input:
(you could say that O2's are just goin' along for the ride )

Tuned Performance

iTrader: (92)

So simply put, you are correct cold start enrichment the o2 is not used until the ecm detects ect 146f o higher and o2 movement at 5-600f.

vetteoz

iTrader: (13)

To bad there are so many mistakes in that article.

The OP switch for example will not turn off the fuel pump with low oil pressure because the pump has a separate independent supply from the pump relay run by the ECM

vetteoz

iTrader: (13)

"Loss of the O2 sensor a well tuned engine will have no impact on the AFR "

Maybe"Ray" should have read O2 sensors 101 before writing the article.

The O2 sensor is the most critical element in a ECM controlled engine.Without it the ECM has no feedback what the engine fueling is doing

"The computer uses the oxygen sensor's input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop."
The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change
in the O2 sensor reading.
This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture.
The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency
while keeping the average overall fuel mixture in proper balance to minimize emissions. It's a complicated setup but it works.

When no signal is received from the O2 sensor, as is the case when a cold engine is first started (or the 02 sensor fails), the computer orders
a fixed (unchanging) rich fuel mixture. This is referred to as "open loop" operation because no input is used from the O2 sensor to regulate the
fuel mixture.
If the engine fails to go into closed loop when the O2 sensor reaches operating temperature, or drops out of closed loop because the O2 sensor's
signal is lost, the engine will run too rich causing an increase in fuel consumption and emissions.
A bad coolant sensor can also prevent the system from going into closed loop because the computer also considers engine coolant temperature
when deciding whether or not to go into closed loop."

Tuned Performance

iTrader: (92)

Ray B hasn't meet Jack S