https://www.rockauto.com/en/moreinfo...pt=5128&jsn=20

 

If I unplug the MAF the B1/B2 STFTs drop to 20%/13%, which is wayyy better. Does this confirm a bad MAF? Probably with a large vacuum leak? Getting the truck smoke tested at a local shop in a week.

 

Have you fixed the canister yet? Is your intake stock or aftermarket?

 

All stock exhaust with no modifications. I havent fixed the canister yet since I have to move the exhaust first. I figured the VMV was closed and I tried plugging the vac hose to it just in case it was stuck open but that had no effect.

I checked the vacuum at the brake booster tonight at idle with the engine cold. It looks like it was holding steady at 19 in-hg. I was leaning towards an intake manifold leak but now I'm not so sure? Could I still have a bad enough vacuum leak to cause max fuel trims but steady good vacuum at idle? Should I go back to looking at a MAF/O2 sensor issue, or is there something I'm missing?

 

Is the INTAKE stock or is it something like a K&N? I would REALLY suspect that MAF.

 

The intake is 100% stock with a normal looking filter. I ordered a new motorcraft filter just in case. I think its definitely odd that the trims immediately reduce by like 30% both banks when I unplug the MAF. So I ordered a new motorcraft MAF sensor hopefully that helps! I also tried disconnecting the O2 sensors one at a time just to see, with and without the MAF plugged in and got the following (trims are ST+LT):
MAF plugged in, B1 O2 in, B2 O2 in = B1+55%/ B2+55%
MAF unplugged, B1 O2 in, B2 O2 in = B1+25%/ B2+20%
MAF plugged in, B1 O2 in, B2 O2 disconnected = B1+53%/ B2+50%
MAF unplugged, B1 O2 in, B2 O2 disconnected = B1+25%/ B2+5%
MAF plugged in, B1 O2 disconnected, B2 O2 in = Stays in Open loop then stalls.

Any thought?

On a separate note, working on this truck (outside) has been making me pretty lightheaded, could the fumes from running so rich or something else burning (coolant, brake fluid, etc) cause that?

 

Yes, the rich fumes can do that.

 

So as a few of you suggested it did end up being the MAF! Even though it was brand new (off-brand, unlabeled) it was causing all the issues. I bought a new motorcraft brand MAF, reset the KAM and my trims for B1 dropped to around +12, B2 around +4 at idle and no more stalling at idle. Which is way way better and no codes. Still have an small issue with B1 apparently and still have a fuel smell but a huge improvement. Thanks for all the input!

 

If you have a fuel smell you may have a leaky injector. The 2005 5.4 had a bad batch that did exactly that.