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Old 03-17-2006, 06:37 PM   #1
Scooby Newbie
Member#: 103392
Join Date: Dec 2005
Location: Houston
Default CAI running lean, rich? What about O2 sensor?

As appears to be common knowledge on this website, a CAI or intake other than stock can throw off the calibration of the MAF causing the engine to run lean, rich, or just not as smoothly. Could someone who is familiar with the stock EM explain to me what relation the MAF sensor and O2 sensor have with each other and making the car run lean or rich. As I understand the O2 sensor measures O2 in the exhaust to see if is rich or lean and modifies the incoming fuel accordingly.

I just fixed a salvage wrx, with front end damage. Because the stock plastic snorkel/silencer/cold air scoop where smashed I have just been running the top half of the airbox (with filter), and now the entire airbox (top and bottom together) until I can get the other parts. I should'nt be to far off the calibration of the MAF, right? Would this setup cause me to run lean? What are the dangers of running lean? Is it ok to run this setup and not get the other stock intake parts?

Any advice is appreciated.
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Old 03-17-2006, 07:27 PM   #2
Scooby Specialist
Member#: 86665
Join Date: May 2005
Chapter/Region: TXIC
Location: Frisco, TX
2005 WRX SRR 2.5/20g
2010 FXT SWP Cobb Stg2+


The amount of adjustment the o2 sensor gives is small. The ECU can trim out smaller adjustments but if the intake measurements are way off (more air entering than the ECU thinks), it can run lean. Lean on a boosted motor can more easily cause internal damage.

Hard to say from your description, you might be OK. Snorkel deletes are common. If you want to know for sure you might hook up a wideband.
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Old 03-17-2006, 07:47 PM   #3
Scooby Specialist
Member#: 56321
Join Date: Mar 2004
Chapter/Region: NESIC
Location: Hopkinton, MA
2006 Honda El Camino


The reason why intakes often screw with MAF readings is because they are improperly designed. They either cause turbulence around the MAF sensor, screwing up readings and making them inconsistent or they have inner diameters that are not what is expected by the MAF. The MAF is calibrated to 'expect' a certain diameter pipe around it and if this is changed, the car will start running lean or rich.

As long as the top half of the airbox and the tubing containing the maf are okay, I think you should be fine. You may get extra hot air from the engine bay without the bottom of the air box, however, the MAF will account for that.

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