Hey guys. My 1998 C1500/Silverado with 5.0 Vortec was going thru antifreeze so I figured intake manifold gasket job was needed. I did that, along with new valve cover gaskets. Used the Felpro kit. Just before I did the job I -think- I got a P0420 code. I wish I had wrote it down at the time but I did not. So I went and did the gasket job. Everything back in place fine and I did a smoke test and no leaks could be seen. When the truck is cold and I first start her up and giver her gas she'll hesitate a little at first and then she'll be fine. After that no hesitations any time thereafter until she's cold again. Now a few days later I get the P0171 and P0174 codes for both banks being lean. I cleaned the MAF sensor with MAF cleaner. No change. I smoked the engine again and still see no leaks. Fuel consumption seems about the same. What should I check next? Any help would be greatly appreciated.

 

OK guys. I did the vacuum leak test using propane and I smoked the engine again. No leaks from what I can tell. I checked the STFT and LTFT and the LTFT is at 25% and does decrease when I rev the engine. I took the MAF sensor off and slightly warmed it with a heat gun and then applied MAF sensor cleaner to it. Reinstalled it and no change. I had forgot that every now and then when I start the truck I hear something like a vacuum/slight whine sound coming from the rear underside somewhere. I'm wondering if it's my fuel pump going or if it's somehow working hard because the fuel filter is clogged...? I bought a fuel filter and will do that tomorrow.