Originally Posted by Paul1958
38-40 psi relative fuel pressure is normal/correct. Just curious - when was the last time your Focus had new O2 sensors? Have you looked at the O2 sensor voltage output in scan tool live data? Lean condition can be lack of fuel or too much air (leak). What are your ST and LT FTs?
Last time I changed the O2's was soon after I purchased the car, as a preventative measure thing as I didn't know when or if they were changed, and that was about 110K miles ago. The one that I had took out was still "good" so maybe I will try swapping it back in in the interim, and replace it with another Motorcraft one.
To amc's post: I do not believe that hose is the issue as today when I went out to the car (was unable to get to it either Friday or Saturday) the car ran fine like nothing ever happened, so it would not seem that hose would be at fault as if it failed would it not be still failed and causing the issue even after waiting 48+ hours? Took the car on a road test today no issues, including to highway speeds.
I suspect it is something heat related as the car was sitting and we did have snow yesterday night (though all melted by late this morning), and on the day the issue happened was warmer but far from extreme, but a lot of stop and go mixed city and highway driving. Perhaps it is the front O2 sensor maybe developed a fault that make it seem like the engine was running drastically lean, maybe it was some other issue and the O2 was just reporting the actual facts. Will have to see how the car behaves over the next couple days, but may be prudent to replace the front O2 in any case and see how things go. I've been doing my own car maintenance for 20 years now and never recall seeing a similar thing happening.