Question: I have a 2000 Chevy Silverado 2500 with a 6.0-liter V-8. It's hard to start when cold. I have to crank it for a while, and it runs rough and stalls for about 15 minutes after that. Once it warms up, it runs great with no problems. How can I straighten it out when it's cold?
Answer: Dealing with a cold-start condition is a process of elimination by running certain tests in the correct diagnostic order. The first test requires a scan tool to view powertrain control data. Engine coolant temperature and intake air temperature sensor voltages are the key. The engine requires more fuel for cold-temp operation. So the Powertrain Control Module views temperature information and commands the appropriate amount of fuel via the injectors.
When the temperature data is incorrect, there are problems. You want to see accurate temperature readings on a cold engine; if it's 80 degrees F outside (or in your garage), you should be looking at similar numbers for coolant and intake air. If the numbers are off from ambient temperature, or intake air and engine coolant sensor readings don't match (on or within a few degrees), that must be corrected before you go any further. It's possibly a bad sensor, high resistance in a sensor circuit, and so on.
Other items to check: Fuel pressure needs to be tested with a gauge, gas should be checked for contamination, the proper operation of the Idle Air Control valve must be confirmed, and the throttle plate in the throttle body assembly should be cleaned of carbon buildup.
If all that checks out, you're likely looking for an atypical failure such as a valvetrain problem or even a blown head gasket. When a head gasket leaks coolant into the combustion chamber, it will sometimes trickle into the cylinders while sitting overnight. This will
give you a hard-start, run-rough situation until the coolant burns off. Start from the top and work your way down.
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