I have a 2006 Lincoln Mark Lt with 90,000 miles that works fine in 4x4 low, but will not engage in 4x4 hi. The light on the dash comes on when I switch it to 4x4 hi, but it doesn't engage the front wheels. Does anyone know what it might be, or what it wouldn't be? I have done some research but not found anyone with this problem. I have seen that common issues are the actuator, and the IWE solenoid, but it seems strange to me that 4x4 Low still works. I was hoping that someone might be able to diagnose it based on what its doing so that I dont have to take it to the dealer to figure it out...

All help is greatly appreciated

 

when you say 4 low works, is the front shaft spinning? Or does it just drop to the lower gearing with only the rear shaft engaged? maybe a chain?

 

Ok I was mistaken, the 4x4 does not work at all. It was in fact just dropping down to a lower gear but not engaging. I have done some more research though and done a little trouble shooting. When I put it in 4 wheel, the drive shaft from under the cab to the front axle will no longer spin freely. I hear actuator(motor directly under cab) shift, and pulled it off and noticed that it seems to be operating correctly. This leads me to believe it's good up to the front axle. I also pulled the vacuum hose off of the front hub on both sides and put my finger on it and could NOT feel any vacuum at all(both in 4x4 and 2x4).

From what I've read, it should have vacuum on it while in 2 wheel drive, and when the vacuum is released it slips into 4x4. Is this right? Since I just bought this thing I'm thinking who ever had it before me, had the vacuum selenoid(looks like its the original) go out and then they may have just let it chew up the front hub and splines inside. Am I way off or does anyone know if that sounds accurate??? I am wanting to know what to replace, because it seems like I need to replace the hubs and vacuum selenoid.

ALL HELP IS APPRECIATED!

 

Did you ever figure out your problem?