Single o2 sensor setup

I got rid of it for a few months when I replaced the o2 sensor shortly after getting the truck. It came back after my alternator upgrade (130amp) cleaned the connector and it disappeared for a few days. Now it's back. I had an extra sensor (unused) and that didn't help. I can't find any leaks in the exhaust before the o2-doesn't mean they are not there. I don't have MAF. New silicone vacuum lines (all of the small one's anyway). Had IAC and TB gaskets so I put them on (TB didn't have a gasket so I figured I had found the issue) but that still didn't help.

I don't have any other issues, runs good, doesn't stall or stutter, plenty of power, idle's smooth. Just keep getting this running lean code and I know the computer is running her rich to try to compensate. Any ideas on where/what to check would be appreciated. Spent the last day and a half researching and trying to find problems but haven't located anything.

PS: Planning on grabbing a fuel pressure gauge tomorrow to see if that could be causing this.

 

I like the 02 posts. I find them educational and entertaining. What r you going to test first?

 

My guess right now is exhaust leak just because it runs like a top other than the 172 tripping the CEL. Just not sure if there are places that leaks usually happen in, don't really want to pull the exhaust if I don't have to.

 

Just a question, if your timing is advanced, would that throw a lean code?

 

I'm not sure, but I've never advanced the timing.

 

Smoke test it. There's a fancy machine that nobody has but you should be able to figure out a way to redneck it. Just crank the motor with the ignition off and suck some smoke through it. Block up the tailpipe a bit and you should see any leaks

 

Just pull engine vacuum.

 

I'll vac test the engine tomorrow, and I've seen people use cigars to smoke test-don't have cigars but I got 3-4 cartons of cig's so I think I can figure something if the vac test reveals a leak.

 

Vac held at 20 while warming up then dropped to 19 and held steady. Blipping the throttle it dropped to 10ish then rebounded and held at 19. Going for fuel pressure tester in a few minutes.

Forgot to say that the light only comes on after a few minutes of driving, then disappears upon restart only coming back after a few minutes of driving. Let the truck warm up the other day because it was cold outside and I wanted to be warm and the light didn't come on until driving for a few minutes. I'm thinking it's got to be a small leak somewhere in the upper exhaust but don't know how to track it down. Going to rule out fuel for sure today.

 

19 is not 2 bad.