I've posted a couple of times about a lean running 5.4. I've got a bunch more information so I'm starting a new thread keying on the problem.
When I start the truck, the Short Trim on both banks behaves reasonably. Mild variation from about -2% to +2%. The Long Trim immediately goes to +25%. Revving the engine to about 1,700RPM reduces the LT to about 12%, but it immediately shoots back up to 25%.
After a few minutes, both banks throw lean codes and the Check Engine light comes on.
This started more than a year ago when the O2 sensor on the right bank failed. The sensor was replaced and all was normal for a couple of months. Then the lean codes started showing up.
I've replaced the fuel pump, filter, and fuel pressure regulator, yet the problem persists.
Any 5.4 guys out there with an idea, I'm all ears. I'm out of ideas.
I've been on the road (with a different vehicle!) and haven't had a chance to test it yet. If the weather holds, I've already informed the boss (wife) that Sunday is "vehicle maintenance" day. I'll let you know what I find.
Well this went an entirely different direction than I had expected.
I replaced the fuel pressure regulator and all of the lean issues seem to have resolved. I've put about 2 hours on the truck since then, with absolutely no indication of a problem.
Two different Ford mechanics told me that the pressure regulator had tested OKand in good-natured fashion laughed at me when I told them that I was going to change it. "That's a waste of money. The regulator tested out fine". (3 fuel pumps and 3 filters later, I replaced the $30 part.....)
Apparently, they're not just pass/fail as long trim now varies from -3 to +3, where it was locked in at +25 before.