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Need help with an on going problem.


December 13, 2008
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I havea 2003 Explorer 4x4 4.0L sohc. Been having problems with mis fires and the engine chugging, running rough. I've put new plugs and wires, and replaced an O2 sensor(bank 2 sensor 1). It's been running okay for the past 3 weeks(since I replace the O2 sensor), but it started acting up again. The CEL is on now and it also blinks at me while driving. I had auto zone check the codes and got some new ones.

The codes:
P0171 - Fuel trim bank one condition
P0174 - Fuel trim bank two condition
P0302 - Cylinder 2 misfire
P0306 - Cylinder 6 misfire
P0300 - Random cylinder misfires
P0316 - Crank sensor condition

Autozone told me it could be a Mass Air Flow sensor, but he didn't seem to sure. Any suggestions, ideas?


EDIT: forgot to mention that about a week ago, there has been a semi loud knocking noise at cold starts, but it goes away fairly quickly and it doesn't happen all the time. (maybe 3 out of every 5 cold that noise would show up)

I took it into the shop, they ran all the tests they could(fuel presure, MAF, coil, plugs/wires and O2 sensors) and they reset the fuel trim values. It was running rich,
-25% both banks. Turns out that both downstream O2 sensors are bad, causing the misfire.

How hard is it to replace both downstream O2 sensors?

I replied on the other post before i read this one. A bad crank sensor will either cause your engine to not run at all (becuase the PCM doesn't know where the pistons are compared to the cam timing, so it doesn't know where to inject fuel.) Or if it was an intermittent deal it could very well cause random misfires, due to same reason stated before.

If the circuits for the crank sensor are good then its the sensor most likely. (Could also be main bearings, more diagnosis needed to verify that though. Kind of doubtful that there is that much play in them to cause a crank sensor to read incorrectly.)

I suggest new crank sensor and see what that does for the random misfire code. I have seen vehicles with bad crank sensors many times. Ford just recently had a recall for certain 7.3 diesel crank sensors. They were screwing up and leaving the drivers in tennis shoe mode.

The likely hood of two 02 sensors going bad at the same time are slim to none, unless they got contaminated due to coolant/oil being burned.