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C2H5OH
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11,867 Posts
https://www.motorcraftservice.com/FreeResources/OBD

If the link does not bring you directly to where it should (doesn't work for me),

Click on 'free resources"

Click on OBDII Theory & Operation
That will bring up a page with a bunch of links divided by model year (MY).
Click the appropriate one for your year and download it.

The guides are very handy in understanding why check engine light come on, what triggers them and such. It's an invaluable resource for everyone/anyone.
 

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C2H5OH
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11,867 Posts
Discussion Starter #7
bump
 

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C2H5OH
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11,867 Posts
Discussion Starter #9
Bump, again.
 

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C2H5OH
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11,867 Posts
Discussion Starter #10
^what he said
 

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Old Phart
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44,595 Posts
Systems description & malfunction indication parameters - Invaluable!

Describes how the systems work & when & how they're tested. If you know what they're SUPPOSED to do, it's easier to figure problems when they don't.

Good reading & reference.
 

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Registered
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215 Posts
CHECK ENGINE LIGHT

automotive stoichiometry

A mixture is the working point that modern engine management systems employing fuel
injection attempt to achieve in light load cruise situations. For gasoline fuel, the
stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel.
Any mixture less than 14.7 to 1 is considered to be a rich mixture, any more than
14.7 to 1 is a lean mixture - given perfect (ideal) "test" fuel (gasoline consisting
of solely n-heptane and iso-octane).

As engine components age, parts-gaskets-seals deteriorate, intake,exhaust, sensors, ect.
The Brain - ECM compensates if you have a vacumn leak by adding more fuel,as the O2 reports
a lean condition. If an injector is stuck open the engine runs rich, and the ECM compensates
by restricting the injector electrical pulses that open its pintols. When these factors get
out of the range of compensation, the ECM sends out a check engine light signal.

Heres good reading:
http://www.youtube.com/watch?v=5WnM_NsOtd8
http://www.youtube.com/watch?v=cARQ0jZZ4Qc
 

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26 Posts
Not to be mean, this is so 30 years ago actually, I had a flash back of an emissions BAR 84 update course for my class MVPC State of California exam!
 

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Registered
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28 Posts
http://www.motorcraftservice.com/vdirs/retail/default.asp?pageid=diag_theory_retail&gutsid=diagsheet&menuIndex1=10

If the link does not bring you directly to where it should (doesn't work for me),

Click on OBDII Theory & Operation
That will bring up a page with a bunch of links divided by model year (MY).
Click the appropriate one for your year and download it.

The guides are very handy in understanding why check engine light come on, what triggers them and such. It's an invaluable resource for everyone/anyone.
FYI: Link is dead. I don't think this needs to be a sticky anymore.
 

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C2H5OH
Joined
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11,867 Posts
Discussion Starter #20
The link changes from time to time. I've had to update it 3 times prior IIRC, this being the 4th.
I found the new/current link and it should be updated shortly.

I'm glad people still click it and want to learn more about how the systems interact.
 
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