1995 Lumina - Running rich and dies

Hi,

New to the board. I have a 1995 Lumina, and she's been a great car til I let her to my Sister. When I got her back, it has 147,000 Miles, and the engine service soon light was on, and she's running really rich. So rich that she starts, but after a 1-2 minutes of idling, she'll start puffing black soot and die. The Emissions test was ok, and the last mechanic I took it to said that one of two sensors were bad. He replaced the one sensor, and said something to the effect that the engine temp sensor was registering normal temp, but the other sensor was telling the engine it was -20 degrees outside temperature. Does that sound right? I would really like to salvage this car.

Thanks

It could be several different things. My ranger did exactly the same thing and it turned out to be the oxygen sensor. My z34 did it and it turned out to be the coolant temp sensor. If you start your car and the cooling fans come on right away, than it is most likely the coolant temp sensor. Its best to pull the trouble codes and see what the car says it is. Bend a paper clip into a U shape, Place the ends of it into the plug under the dash, (top row of holes, last two holes on the right.) turn on ignition and count the number of flashes on the check engine light. The first should be one flash followed by a pause and then two flashes. That is a twelve and indicates that the system is functioning. Than will come the reason the light is on. Hope this helps.

To test that theory, measure the resistance of the coolant temperature sensor at a known (or presumed) coolant temperature. An open circuit (unplugged sensor or cut wire) or very high resistance at the sensor will indicate exceptionally low temperatures to the PCM and cause a mixture enrichment. Compare the measured resistance to the chart:

http://72.19.213.157/files/CTSMAT.gif

My guess is that the car has a 191 CID (3.1L) engine. If that's the case, you can find the coolant temperature sensor (CTS) on the intake crossover, just under and toward the front of the throttle body. It should have a yellow and a black wire connected to it.

If the CTS resistance is out of specification, you can connect another CTS to the harness without even installing it, and the mixture should at least be closer to correct on startup. Replacement sensors are about $10-15.

Thank you, this really helps alot. I'll give both a shot and hopefully I can get her running again. BTW, your right it does have a 3.1L V6.