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Need ideas for my old truck

I have a 1997 dodge ram 1500 4x4 with the 318ci engine. 140,000 miles. Fall 2009 I replaced the CAT (old one had broken loose and was rattling around inside) and both o2 sensors. A few months later, when I’d start the truck cold it would idle fine then as it warmed at idle it would run rough almost quit then idle up and run fine all by itself. When started warm it would idle fine then hesitate while acclerating a few times then run fine. No check engine light. Now, about 10 months later check engine light is on (P0138 o2 circuit high voltage bank 1 sensor 2). I have put about 5,000 miles on the new CAT. I checked the wires and connections for damage and found none. Also, new cap,rotor,plugs and wires.

What did you replace the Cat with? Was it a direct fit, or a universal replacement? The problem could be a bad O2 sensor. Were these OEM or universal replacements as well?

Checking the wires & connections for damage is only the first, most reasonable step. Next you have to pull out a volt meter & actually check the power for circuit.

One other thing you should do though is get a fuel pressure gauge on it, and I’d say pay special attention to the fuel pressure regulator. You can get this code if the O2 sensor is fine but the truck is running rich - possibly from fuel pressure being too high. This can also cause the funny running issues. So you need to know your truck’s fuel pressure range - its probably fairly narrow and check it with a gauge.

cat was a direct fit from Walker and the o2 sensors were Bosch OEM equivilant.