4.6L V8 check engine code 'running lean'

'Check engine' light is on. Auto technician ran computer diagnostic. He said the code showed the 'engine is running lean'. The fuel filter and
PCV have been replaced, but we still get the computer code 'engine running lean'. No visible vaccuum lines off. Technician then smoke tested the engine. Two items showed visible smoke; The EGR valve showed very little smoke. The Idle Air Valve showed more smoke than the EGR valve. The tech suggested replacing the 02 sensor. Can the tech be right about the 02 sensor? Also, I am told there are FOUR 02 sensors on this car. (1997 Mustang GT) How can you check to determine which 02 sensor is bad? Please give dtailed response. Rather than just buying parts, I'd like to try to determine what part is actually bad. If you do not agree that the 02 sensor(s) are the problem, please explain why and suggest what I should do.
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Bear1MustardSeed wrote:

Possible, but the O2 sensors usually throw their own codes. The offending one might not be bad enough such that it does.

Yes, there are four.

I can't because Ford publishes that in a separate manual that was out of print when I went to buy it. But generally speaking I believe it's a difference in voltage output that you would need to look for.

What is the specific code number?
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Bear1MustardSeed wrote:

tech
Perhaps, but I it is my understanding that the O2 sensors are a consumable part and after 10 years probably should be replaced.

The Heated Oxygen Sensor (H02S) detects the presence of oxygen in the exhaust and produces a variable voltage according to the amount of oxygen detected. A high concentration of oxygen (lean air/fuel ratio) in the exhaust produces a voltage signal less than 0.4 volts. A low concentration of oxygen (rich air/fuel ratio) produces a voltage signal greater than 0.6 volts. The H02S provides feedback to the Powertrain Control Module (PCM) indicating air/fuel ratio in order to achieve a stoichiometric air/fuel ratio of 14.7:1 during closed loop engine operation. The H02S generates a voltage between 0 and 1.1 volts.

the
should
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The technician did not tell me what the code was but he said that the code indicates that the engine is running lean. Please advise.
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On Fri, 04 May 2007 12:00:50 -0400, "Bear1MustardSeed"
:>indicates that the engine is running lean. Please advise.
My advice is ask him for the specific code and get a print out of what the code means. He should be able to give you that right off the code machine. With that maybe people can be more helpful in narrowing it down for you.
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Isn't the " Check Engine light" ONLY for emmisions crap..

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yes and no. Yes it's about detecting emissions issues. however emissions problems often mean something isn't right that you should attend to regardless. For instance, a misfire code, just because it's so small to only be detected by the computer doesn't mean you don't want to fix it ;)
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It could be that the fuel pressure regulator is bad and it may actually be running lean.take it to auto zone,they will read the code and give it to you.
Idao wrote:

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You know the 2 most common cause I have found for the that will make that light come on are #1. A bad O2 sensor, which others along with the mechanic have indicated and #2. (believe it or not) is the air filter is clogged. This can happen even with relatively low mileage between filter changes if you drive on dirt roads where the air is very dusty. I would at least check that first since it is a cheap fix if it needs to be replaced.
Idao wrote:

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