i have a 2003 gmc truck 6.6 diesil and it wont start when it is cold .
i have changed the glow plugs,condutor rial,glow plug actuator,fuelfilter.what could be the problem.
The big boys that drive the 18 wheelers have what's called a fuel heater that circulates the gas through a radiator type heater to keep the fuel warm. Paraffin wax in in the diesel fuel and it will clog up the injectors. If you are in cold weather, find a way to keep the fuel in the tank warm. This may help. Have the injectors cleaned and the fuel line blown out to clear it. There is an additive you can add to the diesel fuel to help this. Also, if there is a leak in the injection system and air is getting in, it will cause a starting problem as fuel is not getting into the cylinders. You may be going to a truck repair place to trouble shoot this problem.
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