I have 1999 4.0. I've had bank 1 and 2 lean codes for a while now. Originally tried to find the leak but had no luck. Now I'm back it it again and I'm at a loss. I've tried the usual carb cleaner, water, propane trick , got nothing. I replaced the exauhst so I replaced all my o2 sensors then. I've also replaced my MAF sensor. Replaced pcv valve and hose. I haven't done the smoke test and that may be my last resort. I do have a high flow air filter and muffler I don't know if that could cause the lean codes? Any input is appreciated. Thanks

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1999 xlt off-road 4x4.

I would smoke it, i found three intake leaks and multiple exhaust leaks this way on my Ranger.

I know you said you replaced the PCV valve and hose, but I'm hoping you checked the elbow near the intake manifold for cracks and/or rot?

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2003 XLT 2WD 4.0L V6 SOHC
K&N Intake