Quote:
Originally Posted by uspspro
Shiv,
Why is the header causing the lean code? P0171 is based on the fuel trim being considerably out of spec on the LEAN side.
Please explain... Isn't it usually best to try to avoid disabling system checks unless absolutely necessary?
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From what I've seen the P0171 code is caused by the o2 sensor spacer in some headers that is intended to eliminate the cat inefficiency code (P0420). But what it also does is muddle the size and make it slow to respond. I have not seen fuel trims go out of spec considerably with the header installed. But I have seen this code get triggered during sustained highway cruise. So disabling this code isn't a big deal IMHO.
In our Stage 2 map however, we did rescale the MAF a bit to shift trims closer to 0 during cruise/light throttle. But this was mainly to avoid additive and unwanted long term fuel trim that would otherwise make the car run too rich (for max power) over time. I can turn the P0171 diagnostic back on to see if the code comes back or not.
Cheers
shiv