My truck won't start when the temperature get down to 50 degrees. Runs good on warm days. What causes this??

 

Try replacing the temp. sensor. Not to be confused with the gauge/light sending unit.

 

The same happened to my truck but it would start when cold but it took alot of cranking and waiting. But eventually it got to where it wouldn't start at all. Used to start when it was warm, like if I went to school and them came home around 3:00, fire right up. Ended up the crankshaft postion sensor wire shorted out and fried my computer. Pull computer and keep in a warm place overnight. Like in a bunch of covers wrapped up or near a heat source (but not next to fire or too close to a gas heater) and then when it's cold again like early in the morning; install computer and see if it starts. If not then you ruled out a simple but exspensive fix. If not computer then check your fuel pump relay and asd relays. Check fuel pump operation and then check spark and fuel filter.

 

that thing sticking out of the snorkel of the air cleaner. its got a vacuum line runnin out of it.

try changing that