Re: The Infamous P0171 and P0174 codes troubleshooting
So mine is fixed finally. I thought I had it fixed when I addressed my previously mentioned evap issues but i was still getting lean codes. New MAF, fuel pump and filter, iac, egr, etc trying to avoid the inevitable gasket change. But finally tore into the job yesterday. I was very worried when I got down to the fuel rail and saw that new gaskets had already been put in this truck. Great now what. One thing I noticed though before I even started this job was is when I blew on the vent hose that comes from the oil fill tube I could hear air escaping below the lower intake manifold right by the thermostat housing, so obviously unmetered air was getting into the system and closing this part off meant it was drawing the air in from the pcv side. So I had to go deeper and pull the lower manifold also. The gasket set that was installed, and the new set I bought has two separate lower intake gaskets instead of one large gasket so a sealant has to be used to seal the front and rear valley areas. The previous sealant must have been improperly applied and allowed outside air into the system. So with new gaskets and properly applied rtv I now have a leakproof lower intake manifold and hopefully no more lean codes.
97 4.0 2wd