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Discussion Starter #1
Greetings!

I have a 93 Ford Taurus with 156,000 miles. The Check Engine light has been coming on and off lately and I suspect the Oxygen sensors need replacing. My question is where are they located? I know one is located near the catalytic converter, but where is the other? Thank you.

Regards,
93Blue
 

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Pre-OBDII have one before the cat. If you have two cats then you have two sensors.
 

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I had 1 of mine replaced last year and I was told by Ford there are 4 - O2 sensors in my 97. There are 2 before the cats and 2 after.
 

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i had the same problem but that is because i had an intake installed. Just ignore it if you have an intake....if not it is your sensor
 

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Well you don't want to ignore it. If the computer is telling you the O2 sensors have a problem then you are either running lean or rich. Lean will burn a valve or piston and rich will burn up the cat along, both will reduce your gas mileage.
 

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As I believe is stated earlier, there are only two O2 sensors in pre-OBDII cars. Usually right on or right after the exhaust manifold, but before the cats.

Listen to SHOZ123. You definately want to fix a lean or rich condition.

BTW, welcome to the TCCA!!!
 

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Discussion Starter #8
Thanks for all your responses. I will look into replacing the O2 sensors right away!
Thank you, I'm glad to be a part of TCCA.

Regards,
93Blue
 

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This is from an email I got from AutoTap that helps explain how the O2 sensors work.

QUOTE
First let's take a quick look at what happens when you step on the gas. The computer reads the throttle position (TPS), checks the coolant temperature (ECT), checks the intake manifold air flow and pressure (MAF and MAP), air temperature (IAT) and engine RPM. With all that info the computer then performs a "look-up" function. Similar to finding a coordinate on a map, except this map has many more variables than horizontal and vertical! Once the computer finds the correct coordinate for all of those operating conditions, it finds the result it was looking for - exactly how much fuel to inject for that condition in order to get *almost* the perfect mixture, giving you the best performance, economy and lowest emissions. All of this is continuously recalculated, dozens of times per second.

Impressive! But why is it *almost* the perfect mixture? Because dozens of things could influence your engine to the point where that factory-programmed value isn't quite right. To "close the loop" of information flow, there is a program running on your car's computer that uses information from our friend the Oxygen Sensor to check if the mixture is right where it needs to be. If it's a little off, the computer uses that information to come up with a fudge factor. The name of that fudge factor is Long Term Fuel Trim (LTFT). That value is the amount of correction that the computer will automatically apply to the value that it looks-up. Measured in percent, we typically see stay well under + or - 10% when driving. If it gets over + or - 25%, the check engine light will turn on and a code is set telling you that your engine is running either abnormally rich or lean.

I've simplified this just a bit. Here are a couple of the complications (and there might be a few more that I haven't learned yet). There's another fuel trim called Short Term Fuel Trim. There are also a bunch of those lookup tables for different driving conditions, each one can have a separate fuel trim fudge factor.

So - what does this mean to you? A few things.

First, when you get a code that your car is running too rich or lean, don't rush out and buy new Oxygen Sensors. That's just shooting the messenger. Those codes are usually caused by bad information from one of the other sensors that the computer uses to do its lookup.

Using AutoTap to monitor your engine's Long Term Fuel Trims can give you some insight into its health. Nice low numbers mean that your engine is pretty content using factory-programmed values. Big numbers mean that, for some reason, a big fudge factor is being applied.

Finally, you'll get the best engine power with a nice low fuel trim number. Why? Because your engine quits paying attention to the Oxygen Sensor at full throttle. It still applies the last known fuel trim correction, but since maximum power requires a bit richer mixture than what is ideal for the perfect mix of economy and emissions, you typically get the best performance if a large correction doesn't need to be applied.[/b]
 
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