open/closed loop trouble? 1994 S-15

[antxxny]

My jimmy runs for about 8 minutes and then stalls. If I wait for things to cool down it will run again for less than 8 minutes. At one point I noticed a jump of 1000 rpm's on my tach shortly before it shut off. (engine speed did not change) I have tested the module(ok), replaced the ign coil (old one had 120k on it), replaced the cap, rot, plugs, wires. Still dies after heating up. When this condition is happening I do get power to the coil + module. I have not tested for spark yet because I'm here posting this. I have some ideas on the emmisions where the system either runs on an open or closed loop before the truck heats up. (my knowledge is not strong in this area) Is it possible that a sensor is malfuntioning and shuts down when the switch from open/closed loop occurs? I am pulling no engine codes. (just 12 meaning life is peachy) I have read up to forum page(s) 23 and haven't seen any questions similar to this one. Any help would be outstanding. Thanks!

[JackDaniels386]

it could definately be something with the closed loop situation, but I think that when a sensor is reading something serious enough for the ECU to shut your engine off, it should store a code. the thing where u said your RPMs jumped about 1000 makes me wonder if your IAC valve might be whats causing the problem. If thats not it, im thinking its definately got to be a sensor, or a loose connection somewhere.

[94 Jimmy]

ANTXXNY
How do you pronounce that, is it a family name?
In any case suspect your O2 Sensor, if you have two it's the upstream one(closest to the engine). The oxygen sensor detects the oxygen remaining in the exhaust, but it only works when it gets to about 600 degrees. Until that time the mixture is controlled by data stored in the ECM. If you O2 sensor has drifted out of calibration as mine did, everything will be fine until the computer decides to go into closed loop when the coolent temperature reaches around 150 degrees (about 5 - 10 minutes).
Mine ran OK except on sweeping right turns like freeway on-ramps. The sensor had drifted to a rich reading and the computer compensated by leaning out the mixture. On long right turns the mixture leaned out to the point that the engine quit.
Don't troubleshoot it too much, if you haven't changed the sensor in the last 50KMi just do it, if you have do it anyway. These are often the last thing people think of and are the cause of a lot of failed smog checks.
Good luck, let us know what happens.
See ya
94