EFI question

[jaybee]

Since it turned cold here (12 degrees right now) my son's '91 Chevy Lumina with 3.1 MPI engine has developed an unfortunate tendency to die just as it's almost warmed up.  Maybe it thinks it's carbureted?  Plugs looked good but used up, replaced them.  The plug wires and coil pack visually look almost brand new.  No trouble codes.  Nonetheless it wants to run rich with even a puff of black smoke just as it stumbles.  Cold start is excellent, once it's warm it does fine.  Any ideas where I should look?

[unklian]

The temperature sensor makes it run rich when cold.
What happens when the sensor goes bad ?

[jaybee]

The temperature sensor makes it run rich when cold.
What happens when the sensor goes bad ?

I had that same thought a couple of hours after posting the question.  Can the sensors be tested?

[Jokester]

I had that same thought a couple of hours after posting the question.  Can the sensors be tested?[/quote]



Buy, rent, or borrow a scan tool.  Almost everything can be tested.  I've heard (but not confirmed) that Autozone will perform this service right there in their driveway.  

my two cents


.bjb

[awsum34]

My Blazer was doing the same thing.  Mine was the EGR valve. to much carbon buildup. it kept the valve open.  The car companies run the cars so lean. for the gas milage they have to get.

[SKR8PN]

What you are describing could be caused by any one of a number of things. Is the "check engine" light on? If so,there will be a trouble code/codes stored in memory. Get it scanned and that will give you an IDEA as to where to begin looking.If there is more than one code,clear them out and drive the car to see what comes back. THAT will be the code/codes you want to start with. No trouble codes? It will prolly be a circuit or system the engine controller does NOT monitor.  Try  to find someone with a scanner that has the ability to go into "actuator test mode" and a Lab scope,so you can check the injectors and some of the other wiring,connectors,and sensors. MAP sensor and/or MAF sensor would be a good "no code" place to start

[kb426]

Most sensors can be checked with a volt meter. The problem is knowing what the correct reading is.