 misinformation
I Have an '03 Explorer 4X4 V6 4.0L SOHC. This vehicle runs just fine at speeds around town. The idle is perfect. Problem is that when I get into the gas for entering the highway, passing, ect., when I get to 55-60 mph the vehicle stops accelerating. the rpm's stay up and you can hear pinging. I have to back off the gas, let the vehicle shift and slowly baby it up to highway speeds. During all this, the engine never misfires or surges, but the check engine light flashes before extinguishing.
I thought I had an exhaust problem due to a DTC 0171(Bank 1 too lean). I replaced the bank 1 fwd side O2 sensor (no Fix) I checked all three Cats and found them to be functioning properly (heat wise). Can find no vacuum leaks.
Finally broke down and took it in to the dealer. They ran a diagostic and determined that I had a bad fuel pump (no pressure at high engine rpm). The pump and filter were changed and the PCM cal'd. $860.00 NO FIX
Took it back in and now they say that I have weak valve springs. If this were the case, I figure that the engine would run very rough. Apparently there is a TSB (02-3-2) that rectifies this problem. I read the TSB and it does not seem to be the same problem. Before shelling out another $800, I would like to get more info | 
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