So I just replaced my plugs on my 01 blazer 4x4 ls... ( in the mud it was a great time!) and Replaced them with the Bosch platinum's and now I'm throwing P0171 and p0176( I think that's the right code for bank 2 to lean.) Now my scan tool I can monitor dtc's and fuel economy / use on my laptop and it jumped from 19-21mpg to 30mpgs!!! WOAH!!! Typical use of gas to get to work is about 2.4`2.6 gallons each way and it only sucked down 1.8 on the way home today. So my question would be why with the new plugs is it throwing these codes? I read "P0171 Explained" and tried searching around to see if anyone else had this issue ( which it doesn't seem like they had.) Are the Bosch platinum's running to hot for my engine? If they aren't why isn't my PCM changing the fuel/air ratio? I was thinking that it might be my o2 sensors... but why all of a sudden will it throw a code? I know the o2 sensors have at least 100k miles on them (171k total on the blazer) but it seems the o2 sensors are using open and closed loops when need be. Any suggestions? I also disconnected my air box and ran it 150 miles ago without the MAF hooked up but plugged it in right before the next start up could this have caused it and if so shouldn't the pcm see it again? Thanks -Mark

 

Probably your fuel pump about to die. Most will throw the 171 cod about 2-6 weeks before the pump kicks the bucket.

 

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but will it throw both banks? Isn't there a code for not enough fuel pressure to?