Can you give specifics about plank placement and heat source (position), cooker, etc.
Soak the plank for at least 1 hour in water. Place it with the side you want to cook on for a few minutes over direct heat to disinfect it. Then flip it and place the food on it. Place it over direct heat. It doesn't matter if you use charcoal or gas, both works fine.
If you use a pellet cooker with no option for direct heat, you don't have to soak the plank in water.
Cook on high heat (at least 360°F) for about 15 to 20 minutes.
For the sauce use the following ingredients:
1 TBS lemon juice (or lime juice - in that case use lime slices instead of lemon to put into the salmon)
1 TBS orange juice
1 TBS balsamic vinegar
1 TBS honey
1 TBS mustard
1 TBS minced chives
1 clove of garlic
1 tsp salt
1 pinch black pepper
1 pinch chile powder
Blend that in a food processor and add a bit canola oil.