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[/u]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[/align]

 

The catalytic convertors could do it. You must have them off completely and be able to check them visually or you may as well replace the one on the bank 1 side to rule it out. checking heat output tells you nothing most times. Could also be badwiring inthe fuel pump circuit (possibly solder overload in circuit board). Keep the money and buy parts instead of the computer "trying to help". Almost $1000 for a lousy $150 fuel pump and filter? I'd run 'em over with it and ask 'em "Can you fix it now?" All the money they already got it should be fixed. I could have changed the whole interior color or your vehicle for that much. You could look for a bad fusible link, fuse, loose wire, etc. to start. Sometimes high paid guys miss all the basics. Then maybe clean your battery cables. Check fuel filter - they have 2. Maybe they missed the one not in the gas tank (depressurize your fuel system before you check it though - and don't keep a hot light bulb nearby).