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New Edge Cobras
shaky motor at idle need help
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<blockquote data-quote="Taz" data-source="post: 2418155" data-attributes="member: 2127"><p>Okay, it goes like this: your MAF meter under-reports your air flow, so your PCM WAS providing only enough fuel for the reported amount of air. BUT it's a feedback system, and after finding out (via the O2 sensors) that the mixture was a bit lean by 20%, the PCM richened up the fuel trims to compensate, hence the 20% LTFT's that you are seeing. As long as the PCM can bring everything back into line with less than 25% compensation, everybody is happy, and you're not going to get any trouble codes. It isn't until the PCM can no longer compensate within its +/- 25% range that it begins to complain.</p><p></p><p>That takes care of what's called the closed loop fuel trims. You're okay there. Now, NORMALLY, without a dyno tune to compensate for the skewed MAF readings, you'd actually be RICH whenever you go WOT. The reason for this is that the PCM uses a value called the OLFM (Open Loop Fuel Modifier) to adjust the table lookup fuel values it uses for open loop (WOT) operation, and it derives the OLFM from the amount of compensation it has to provide via the LTFT's. But your tune should have taken care of this.</p><p></p><p>Confused yet? Okay, let me simplify. You're okay in closed loop mode, because the PCM was able to compensate for the MAF meter's under-reporting of the air flow. AND you're okay in open loop mode, because your car has been dyno tuned, and adjusting the A/F ratio is part of that process.</p><p></p><p>T-</p></blockquote><p></p>
[QUOTE="Taz, post: 2418155, member: 2127"] Okay, it goes like this: your MAF meter under-reports your air flow, so your PCM WAS providing only enough fuel for the reported amount of air. BUT it's a feedback system, and after finding out (via the O2 sensors) that the mixture was a bit lean by 20%, the PCM richened up the fuel trims to compensate, hence the 20% LTFT's that you are seeing. As long as the PCM can bring everything back into line with less than 25% compensation, everybody is happy, and you're not going to get any trouble codes. It isn't until the PCM can no longer compensate within its +/- 25% range that it begins to complain. That takes care of what's called the closed loop fuel trims. You're okay there. Now, NORMALLY, without a dyno tune to compensate for the skewed MAF readings, you'd actually be RICH whenever you go WOT. The reason for this is that the PCM uses a value called the OLFM (Open Loop Fuel Modifier) to adjust the table lookup fuel values it uses for open loop (WOT) operation, and it derives the OLFM from the amount of compensation it has to provide via the LTFT's. But your tune should have taken care of this. Confused yet? Okay, let me simplify. You're okay in closed loop mode, because the PCM was able to compensate for the MAF meter's under-reporting of the air flow. AND you're okay in open loop mode, because your car has been dyno tuned, and adjusting the A/F ratio is part of that process. T- [/QUOTE]
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shaky motor at idle need help
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