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I have a 2002 for explorer 4wd 4.0 it won't accelerate. it's fine to 25, but it pings, and won't go over 40. I've changed to the plugs, wires, coil pack and fuel filter. I've also checked the fuel pressure, and it's 65psi. no codes are being set. I've been told plugged cat, but they're welded on, and no way to test them... suggestions? thanks in advance
If you want to test for a plugged converter, you can simply remove the oxygen sensor from the exhaust stream ahead of the converters and see if that makes an improvement. The truck will certainly be louder though and there will likely be a check engine light.
Have you checked for vacuum leaks, made sure the MAF is connected, tried cleaning the MAF (especially if you happen to have a reusable air filter)? How old is the fuel in the tank?
Have you used a scan tool to check for diagnostic codes?