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Old 09-13-2015, 09:00 PM   #1
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More power WITH vacuum leak

Recently my AOS bellows tube had a crack, leading to a P1124 and P1126 whenever I would idle for an extended amount of time. At the same time however, it drove with noticeably more power and a lessened 'flat spot' in the 2000-4500RPM range. Now that I fixed it with a new AOS and bellows tube, it is back (albeit better than before the vacuum leak) to having a slight flat spot in the rpm range. TBH it doesn't drive bad at all, but after having the vacuum leak, I'm curious why there would be more power with the leak...?

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Old 09-14-2015, 10:40 AM   #2
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Butt dyno is my guess. The only legitimate guess I have is that perhaps your maf has compensated trims for your operating conditions. Clean it and reset it, accomplished by pulling the battery cable for 15 minutes or so if I remember from when I replaced my MAF.Your car will then relearn settings.

Last edited by jdraupp; 09-14-2015 at 10:44 AM.
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Old 09-14-2015, 12:53 PM   #3
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Lean is mean... Over time the fuel trim would have tried to compensate for it.
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Old 09-14-2015, 01:35 PM   #4
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So my small air leak, combined with the ECUs ability to enrich the mixture just enough created a pseudo-larger-throttle-body? Maybe I should cut a hole in my new bellows...
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Old 09-14-2015, 03:56 PM   #5
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more air getting in than the maf sees. ecu sees the result in the exhaust and tries to add more fuel to compensate. this is because the ecu wants, at idle and cruise, for the mixture to be 14.7 parts air to 1 part fuel (the 'air fuel mixture' or afr). once the ecu adds about 20% or so more fuel and still can't hit 14.7:1 afr then you get the code.

when hooning around the ecu tries to add a bit more gas to the ratio (ie, 12.5 parts air to 1 part fuel) in order to keep things cool. the ecu defines 'hooning' by throttle position (ie, 'wide open throttle' or wot) rpm, engine temperature. this 12.5:1 afr makes less power but helps keep the engine alive. unfortunately, the ecu doesn't have any sensors on the exhaust for this richer mixture (the 'narrow band' oxygen sensor used by the ecu can only detect an afr of14.7:1) so the additional air sneaking past the maf goes undetected, leans out the AFR, and you get more power. and your engine runs hotter.

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