Explain why koer code 41/91/12 would go away with increased fuel pressure

[bsedwebt70-5.0]

Been checking codes and fiddling with things and checking again - finally adjusting fuel pressure up 1 turn got rid of these codes - Anybody know why? or is this a fluke? NO koeo codes at all

 

[HISSIN50]

41/91 are lean codes. You temporarily richened the mixture by increasing FP with the old injector pulsewidth. Once the puter realizes what is going on (assuming O2's actually work) it will adapt the pulsewidth down (so you are still squirting the same amount of fuel as before the FP change) and the codes will probably pop back up (they might not, but it is likely).

12 is probably IAC related. Not sure why that changed.

Good luck.

 

[Grn92LX]

Like I told you on corral.net, I had code 91 with a check engine light when I first got my 347 running. I had a few vacuum leaks that i had to fix. My wideband showed very lean too with the vacuum leaks. One vac leak was at the lower manifold and the other was a vacuum port on the upper manifold I completly forgot to plug.

 

[bsedwebt70-5.0]

41 is baaaack -- I found a loose pcv valve and lowered the fuel pressure and I get 41 every once in a while - not every time I check but 1 time out of 3 or so. Still no 91 or 12 again though - any ideas - could I have installed a bad o2 sensorn that only works some of the time?