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Banks Too Lean


New Member
November 6, 2013
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Year, Model & Trim Level
1999 Ford Explorer XLT
I have a '99 Explorer XLT 6 cyl. SOHC. So my bank 2 is running to lean and my bank 1 has a "pending code" being too lean. According to my scan tool, my LTFT WAS about 10-15% (going up higher at idle) in both banks. Now, a couple days later, it's up to about 23% at idle in both banks and goes to 17ish% while driving. I briefly looked under the hood and didn't see any obvious leaks. I did take off the intake manifold and go through and clean everything when I first bought it and can't remember if I put a new gasket on or not so that was my obvious first assumption. But the fact that the long term fuel trim has jumped so much in the last couple days (enough to trigger a code) makes me suspect something else, but I'm not sure what.

Any ideas? I did replace both oxygen sensors as I had gotten a code previously about a faulty O2 sensor so I just replaced both. I cleaned the MAF as well. And what should the MAF readings be? I believe mine were .01 to .11 lbs/s or something like that.

intake leak

A small intake leak will have the most effect at idle. Since your trims are higher at idle than cruise I suspect you have a leak. Gaskets shrink with age and cooler temperatures. If you replace your upper and lower intake manifold gaskets I suggest that you also replace your EGR tube O ring. Here's a link to intake manifold vacuum connections: Intake manifold vacuum lines