Yash619

I have a 98 Cherokee that's in rough shape, I have just done water pump, thermostat, thermostat housing radiator hoses, distributor cap and rotor, wires, plugs and injectors.

I have a rough idle with a mild back fire in the exhaust. When I rev it up to 2000rpms it smooths out, if I hold it there for a minute then let off it tries to die. I'm getting a code for oxygen sensor 1 bank 1. I looked up under at the exhaust after running it and the catalytic converter was cherry red.

I replaced the injectors due to unplugging the #6 injector while running and it made no change in how the engine ran then did a resistance test and #6 tested bad.

Any ideas on what's going on? I'm thinking it's going to need a new catalytic converter and the bank 1 sensor 1 oxygen sensor.
Could it be a bad valve spring? Or cam problem?

Thanks for the help!

tjwalker

I'd chase the problems you know you have before considering more complex issues.

If you're replacing one oxygen sensor, I'd replace both. They don't last forever. Use NTK brand. And it does sound like you might need a new cat. After these repairs, clear codes and see how it runs and if any codes return. Converters will get red hot when excess fuel is introduced directly into it, along with sufficient oxygen to burn the fuel. This is not a problem with the converter itself, but the result of a problem with the fuel system or ignition that allows unburned fuel to pass through the engine and then travel down into the converter. If the root cause is not corrected, the new converter will melt as well.

Don't hesitate to put an engine analyzer on it or a scan tool to get some real time data of all engine management systems. If the engine has a lot of miles, a compression test is never a bad idea; it's a good "snapshot in time" of the internal condition of the engine.

Yash619

Thanks for the info.
I've done a compression test already I have good compression.

xjchrisc

My 96 model did something pretty similar. Ended up being the coolant temp sensor was bad. When the sensor went bad the computer thought the coolant temperature was was like -40 degrees. The computer tried to compensate by adding more fuel to the combustion chamber to bring up operating temperature.

Yash619

So I got the oxygen sensor replaced, and just for the hell of it I tried the coolant temp sensor. I'm still getting a rough idle a mild back fire in the exhaust, anymore ideas?

xjchrisc

Double check the wires going to the oxygen sensor. Mine contacted the exhaust manifold once and melted. I now have them secured with zip ties.