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Discussion Starter #1
Is there any book/web site where i can learn more about the OBD System, and what are the correct parameters suppose to be ?
 

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Could you be a little more specific? LT1, Gen3, Gen4? Tons of tuning help out there for the Gen 3 computers, books, videos, classes. What do you mean correct parameters?
 

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Discussion Starter #4
Could you be a little more specific? LT1, Gen3, Gen4? Tons of tuning help out there for the Gen 3 computers, books, videos, classes. What do you mean correct parameters?
I'm interested in learning about 96-present Stock OBD systems.. And What i mean buy correct parameters is, lets say i look at the fuel trims . Whats normal and whats not for a correct running car/truck .
 

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Depends on what you are looking to do. If you are looking to troubleshoot a 100k daily driver, abnormal high or how LTFT, can indicate things like clogged injectors, low fuel pressure or other issues with fuel delivery. In a car with modified induction/camshaft.exhaust it can indicate a need for VE table adjustment. Fuel trims have nothing to do with WOT performance, as pretty much all of the GM Computers go open loop (disregard O2 readings) when they get to power enrichment mode.
 

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Discussion Starter #6
I'm just looking to trouble shoot a non modded car/truck , that's all .. I ordered an OBD Scaner ,and i would like to know how to fix a problem if there is one. I know that codes don't always mean that sensor are bad.
 

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Well without knowing exactly what the scanner shows it's going to be tough to guess what needs to be repaired. Scan it and then report back.
 

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On fuel trims, you have long and short term, short term are immediate changes and the long term adjusts to keep the short term close to 0%

lets say short term goes -11%, and stays there for a few moments, long term will begin decreasing to keep short term close to 0%. Generally anything between +9% and -9% long term indicates a "healthy" engine. Whenever outside of this percentage look for problems. Also, the phrase long term is a little deciving as it can change very quickly.

Whats the vehicle doing exactly?
 

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Discussion Starter #9
On fuel trims, you have long and short term, short term are immediate changes and the long term adjusts to keep the short term close to 0%

lets say short term goes -11%, and stays there for a few moments, long term will begin decreasing to keep short term close to 0%. Generally anything between +9% and -9% long term indicates a "healthy" engine. Whenever outside of this percentage look for problems. Also, the phrase long term is a little deciving as it can change very quickly.

Whats the vehicle doing exactly?
Thanks for explaining that a little more. I'm just trying to learn more on the how the system works . I don't have a problem with any of my car/trucks , but i have worked on a few with check engine lights on . I was able to correct most of them, just wasn't sure if they were running 100% ...
 
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