Auto Parts: 1998 CHEVY 7.4 STARTING PROBLEMS AND ENGINE LIGHT, coolant temperature sensor, independent mechanic

Question
MY CHECK ENGINE LIGHT STAYS ON WHEN IT WARMS UP OUTSIDE TO AROUND 70 DEGREES AND HIGHER.  I HAD THE CODE CHECKED AND IT SAYS MY O2 SENSORS ARE BAD BUT I REPLACED THEM TWICE.  ALSO WHEN MY MOTOR WARMS UP AND YOU SHUT IT OFF FOR 20 MINUTES OR MORE IT HAS A HARD TIME STARTING BUT DOES START AFTER ABOUT 6-10 SECONDS.  WHAT COULD BE MY PROBLEM???

Answer
    My guess is the coolant temperature sensor.  The computer can determine the health of some sensors, and others are still within their normal range of values when they fail.  The coolant temperature sensor is one of those.  Unfortunately, the oxygen sensor is another.  When the engine is warm, the computer still thinks it is cold, and tries to enrich the mixture to make it easier to start.  But, when the engine is warmed up, rich mixture makes it harder to start.  What you need to do is get a pro to hook a real-time scanner up to the computer and check the function of all of the components.  Just using a code scanner is not really getting you any information, just the best guess of the folks who wrote the software.  With a real-time scan of the engine, a mechanic can determine which sensors are providing what information.  He can compare that to independently measured values and decide what needs fixing.  I know everyone hates paying pros for these services, but you've already bought several parts that you probably didn't need, buying more isn't going to make it better.  Just don't go to a chain-store, tire-store, or franchise tune-up place.  Find a good independent mechanic and let him show you the results he gets and give you his recommendations.  If you don't know of one, go to a local independent (not a chain, like Pep Boys) parts store and ask for their recommendation; they know who the good guys are and are more than happy to steer business his way.