My 1992 Silverado 6 cylinder turns over but will not run if outside tempter drops below 40 degrees, otherwise runs great, already changed battery, MAP sensor, rotor, distributor cap, spark plugs and wires, knock sensor, fuel filter and checked fuel quality and all fuses?

Answer: The next thing you need to check is the coolant temperature sensor. If it is not accurate, it will cause the fuel delivery on a cold engine to be wrong. The engine need to be fuel rich when cold. You can use an ohm meter to check its resistance and compare it to a chart or what the reading should be at certain temperatures. Or you could just replace it since it is quite inexpensive and you already have spent some money on other repairs.

Next you need to check fuel pressure. On this truck pressure needs to be at least 55 PSI. Even a few PSI less and this engine will NOT start. This is even more important on a cold engine.

Another thing to look at is check for carbon buildup in the throttle. This also can cause a hard start or no start on a cold engine. You can usually cheek this by looking at at it or even holding the gas pedal open a little bit while cranking. If it now start, then most likely the throttle is carboned up and needs to be cleaned.