Quote:
Originally Posted by 5GSS
That is correct. MAF measures air mass going in, first O2 sensor measures O2 coming out (to calculate A/F), second O2 sensor measures O2 after cat (to verify properly functioning cat).
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This is what I had always thought. So to sum it all up, if you do LT's without a tune it will not have ANY affect on your A/F ratio as the first set of O2's is what determines that. The second set of O2 sensors are strictly to determine if your cats are functioning properly. If they are not or the second set of sensors is missing, the car will throw a code. The code however will still not affect your A/F ratio. This was the big change with OBDII computers which allowed for emissions to be tested without the use of the sniffer.
Guys that are worried about blowing up their motor because of not getting a tune need not worried. Look at how many people have added LT's to 4th gens and not tuned them.