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2003 Ford Explorer Eddie Bauer 4dr 114 WB 4.0L

2003 Ford Explorer
Trim Info:
Rear Wheel Drive, 4 Door
15 mpg city / 21 mpg hwy
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April 10, 2013, 3:01 pm

Kenneth H

Question: Bank 1& 2 running lean

It has a 4.0 ohv it run rough when started. Engine codes keeps saying bank 1&2 running lean. I have replaced mass air flow, throttle position sensor, and the I'd air control valve and still saying the same thing 1&2 running lean

April 13, 2013, 10:14 am

Ron W
Expert Mechanic

You may have a vacuum leak in the intake somewhere. Have a shop perform a smoke test to isolate if there is a leak. This is assuming it is already tuned up.

Also, do you have a Kand N type air filter?

It’s possible that your MAF (Mass air flow sensor) may be contaminated. If it gets dirt or oil (from and over oiled K&N type filter), it will misread the amount of air coming into the engine. Usually it reads too little air because of the contamination. What happens is the PCM (Powertrain Control Module) reduces the injector on time (leans out the mixture) to compensate for the reduce air flow. What the driver experiences is surging.
You'll need a scan tool to clear the codes. This will reset the adaptives and reset the MIL light.

If you installed a new MAF, but still had an oily filter, the new one could be damaged as soon as it was installed.

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