Hello everyone. This is my first time on the site and I was hoping someone could shed some light. My sister's 1997 dakota 3.9L automatic (rebuilt motor, less than 3k miles) idles erratically when cold, sporadically stalls when accelerating from a stop (though sometimes I can prevent it by giving it more gas), and in the last week stalled twice while driving (once on freeway while cruising and the other on a surface street). The catalytic converter was about 8 months old when we put the new motor in. It's been about 5 months since then and it now has a very noticeable rattle. I hadn't driven it since the motor was installed and yesterday when I picked it up I immediately noticed a marked decrease in power, which I'm assuming is caused by the clogged cat. We had the same problem with the previous motor and went through two cats. As I understand this is because the mixture is too rich. I checked the MAP sensor and got good voltage from the PCM and when back-probing the connection. The TPS got good voltage from the PCM as well but when back-probing I got a reading of 3.84V with the throttle wide open, whereas the book says it should have been 4.5V. I replaced the TPS and now get a reading of 3.74 with throttle wide open. I know I have to replace the cat but I'd like to figure out why we keep burning them up and why the engine has been stalling and idling roughly. Any input would be helpful at this point.

thanks

 

Check the intake man for leaks?

 

if you are still getting 3.7 V at the tps i would start there. have you checked the wires going from the TPS to the PCM? what codes does it have?

and if the intake manifold was leaking it would have a high idle. the above person clearly doesnt know how a speed density intake air strategy works!

 

ROFL.. I guess that is why the number 1 suspect on these trucks is to replace the seals and pan on the kegger eh? Not trying to argue or anything just a thought.. but I understand where your coming from.. but a vac leak on the inside of the engine is not going to raise it.. it would suck in oil more than anything and throw your air/fuel mix off and could cause a ****ty rough idle.

Just some food for thought.