After driving about 50 miles with the 4wd HI locked in, I stopped at a stoplight and got a strong odor of propane. At first, I just thought it was something about the area we had stopped. However, after returning home, the odor filled my garage. I had the 4wd on due to snow and ice, however, some of the drive time was just on pavement. Any help or suggestions would be appreciated...if it matters, I did recently have the solenoid that engages the 4wd replaced. The truck is an '07 F150 Lariat.

 

If you were driving in 4wd on pavement, you may be cooking the transfer case. Better check your fluids.

 

F150 SMELLS LIKE PROPANE: I had also a very strong odor which smelled exactly like propane. (2010 F150 SCREW 5.4L) You could smell it inside or outside the truck.
There turned out to be 2 causes.
The first was that the U joint type mechanism (I think its called a propeller joint) on the end of the front driveshaft where it enters the front differential had the seal blow out, and was flinging grease onto the exhaust pipe, which created an odor burning off.
The second source was the vent hose for the front differential, which is located by the master cylinder. The odor coming out of it also smelled awful, like propane. And due to its location, the odors were sucked right into the cab.
Had the differential opened up, cleaned out and the fluid replaced. End of stink!!
My mechanic said the odor was so bad, he had to put fans in the doors to air out the shop!

 

Ahh, the joys of working in a shop... I guess it was better than running over a fresh skunk then having them work on it.

Skunk versus propane smell... dunno... both stink!

All comedy aside, glad to see it's resolved.