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Old 06-20-2005, 09:06 AM   #1
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Fuel/air ratio's

I have a few somewhat technical questions on the fuel/air mixutures of the boxster. I have heard that increasing the air flow through the intake and exhaust ends of the car lean out the mixture. I've also heard that running the car lean can lead to fried piston rings or pistons or something to that nature(please correct this if this is wrong because I can't remember exactly). I have also read that the ECU on our car self-adjusts and recalibrates the A/F mixture when it senses it is running lean or rich. If say an aftermarket intake and headers/cats/exhaust are added would this make the car run lean or would it adjust for these modifications? Could these mods harm the engine if the computer is not reprogrammed(ie fried rings)? Would the only way to truly tell what if it is running really lean be placing a A/F sensor somewhere downstream of the engine?

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Last edited by Adam; 06-20-2005 at 09:16 AM.
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Old 06-20-2005, 10:00 AM   #2
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The official Porsche position as I understand it is that any mods made to the intake and exhaust are of concern and likely a warranty killer.

Certainly, the local dealer does not like to work on cars that have aftermarket items of this nature. Having said that, they do have diagnostics that could tell you if your car is running lean or rich and by how much. This is much more sophisiticated than relaying on your CEL to tell you.

As I understand it, yours car's computer can make adjustments to the f/a ratio WITHIN CERTAIN PARAMETERS. If the ratio is way out of whack, my guess is that you would get a CEL but I am not certain.

I will ask the service guys later today.

You are correct in being concerned about any f/a alterations as nothing good can come of them. Fouled plugs to lunched pistons, it is all bad news.

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Old 06-24-2005, 06:33 PM   #3
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The computer does try to re-mix depending on what the sensors all say. The O2 sensors feed info from the intake and exhaust with how much oxygen is coming in and how much is going out after combustion. The computer adjusts all of this to help the engine burn cleaner and safer. It adjusts the mixture up to something like 10 times/second so it's constant adjustment.

Like Brucelee says, there are certain parameters set in the computer that determine how to change the mixture. If it can't get back to the parameters you will get a CEL and could damage the engine. The only way to make the computer accept the new parameters is to re-program it (good luck) or put a chip in that will do the re-programming for you. I'd think twice about it, though. The computer was designed to protect the engine and make it perfom at its' best. If you change the parameters and the computer does not realize the engine is being harmed, you lose all of your protection.

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