1985 Cadillac Eldorado Convertible

[Bry85]

My Eldo was spewing what I thought was excessive "white" smoke from the exhaust. A mechanic looked it over and said it was "blueish" smoke due to a faulty sensor that was located in the dash board behind the glove box. Can anyone elaborate on what this sensor was?

[76eldo]

Try a different mechanic.

Brian

[TJ Hopland]

I cant think of a sensor inside that would do that.  Behind the glove box would be parts of the heat/ac and maybe the ecu.

[Bry85]

The mechanic referred to it as a ""Map Sensor".  Seems to have fixed to problem!

[76eldo]

Did the ECM record any codes?

If the MAP was that far out of whack I would think it would turn on a service soon light.

Brian

[TJ Hopland]

The earlier systems (say pre mid 90's) were not that smart when it came to bad sensors.  They could tell if the sensor was open or shorted but as long as it was getting a reading within a set range it thought it was alright.  So what likely happened is his sensor failed in a way that was giving the computer a reading that made it think it was under heavy load (like towing or hill climbing) all the time so it was adding extra fuel when it was not needed.  Newer systems have more computing power and lots more software running all the time checking things like that.  A new system would be smart enough to see that the reading is not changing like it should in relation to other sensors and then flag it as a possible issue.   I knew the 70's map sensors were on the ECU.  On other 80's GM stuff I had worked on the map sensor was either on the intake manifold or firewall under the hood.  I assumed cadillac was the same, guess not.  The map sensor is Manifold Absolute Pressure or what most people would call vacuum.   Its used to help judge the load on the engine and then adjust fuel accordingly.   

[Bry85]

From what I was told.....the sensor wasn't reading on the mechanics diagnositc computer and the car wasn't telling me of anything in need of service. I'll drive it around today and see how it goes!

[TJ Hopland]

Seems odd but if its working now.....

Another thought is I wonder why it did not trip a light for a rich condition, usually something like O2 sensor out of range?  The only way it should not have done that is that it does not think its warmed up so its never looking at the o2 sensor.  I dont remember if there is a way to tell if its in 'open loop' mode or not. There is something in the back of my mind from when I had my 83 but I dont remember the details. Thinking perhaps the torque converter wont lock up till it thinks its warmed up.   You can usually feel that if you lightly put your left foot on the brake pedal while maintaining your right foot on the gas, this should unlock the torque converter which would usually be a 2-300 bump in the rpm and then releasing the brake would drop it again.  If it does not do that it may have a problem with the coolant sensor.