I really hate posting this because I know it has been posted so many times on this forum but it seems that mine is a little unique and I would like some input.

98 F150 XLT 4x4 Supercab Short Bed with almost 200k, when I first bought the truck (a month ago) it was throwing a few misfire codes (I don't have the codes anymore) the guy told me it just needed a tune up and he had already bought the parts so I went ahead and did the tune up (Motorcraft plugs and Autolite wires.. Again he already bought it so I just went with it, lol) and all the plugs looked about the same so seemed pretty normal. After doing the tune up the check engine light went out and the truck was running 100x's better.. truck still seems to be running fine now but is a little less powerful than I had expected having never owned an F150 from this generation of trucks.. A day or so later check engine come on again with one code (I don't have the number Advance read it for me and I didn't write it down) lean bank 2.

I've read here to check the pcv valve and its boot/elbow, now in theory shouldn't that throw a code for both banks? I am still going to check that but I'm just trying to bring some logic to the table.. What vacuum lines effect bank 2 because they all look really good.. There is one hose coming off of the top of the passenger valve cover that goes wherever it goes and it has what appears to be a vacuum fitting but isn't connected to anything and I couldn't find any lines off anywhere so I'm at a loss as to what else it could be. CEL is driving me nutts

Any help would be greatly appreciated , Thanks Guys...

-Aj

 

The vacuum system is common to both banks. An intake or exhaust gasket leak or exhaust system leak(before the pipes merge) on bank 2 could set this DTC. If you have someone spray the intake while you monitor your STFTs you can pinpoint the leak.

 

Ok, that makes sense I don't believe I have ever heard one of these generation of trucks without an exhaust leak (ticking noise) seems pretty common. I do have an exhaust leak right at the doughnut between the manifold and the cat, didn't think it was bad enough to throw a code?

So in theory, correct me if I'm wrong but, the exhaust leak causes the o2 sensor to get an incorrect reading therefore making it think that side is too lean? I believe I read a post somewhere that says if it reads too lean its actually rich and the computer is leaning it out (sounded a little weird but who knows)

 

If an exhaust leak is only monitored by bank x bank y won't see it and won't report it. If the leak is that far downstream it might not effect the A/F ratio on either bank. An exhaust leak does cause a lean condition(adds air). If it's lean it's lean. If it's rich it's rich. The computer doesn't make it rich or lean. The computer tries to bring the A/F back to Stoich when it detects a rich or lean condition. If it is lean it adds fuel(longer PW for the injectors). If it is rich it pulls fuel(shorter PW for the injectors). The fuel strategy is ADAPTIVE in that it is always trying to keep the A/F ratio at 14.7:1 to satisfy the EPA. Once it can't compensate anymore the SES lite comes "ON".