Hi guys about four months ago I bought a 2002 SuperCrew f150. When I bought it I knew the four-wheel-drive didn't work. But I need to get it fixed now because I work construction and I'm constantly getting stuck in the mud.

so last night I decided to do some testing after reading and watching a bunch of YouTube videos. Here's what I know.

If I put the truck in 4-wheel drive on the dash, the four wheel drive indicator does not come on unless I leave it and drive about 10 miles. Even when it does come on it's not actually engaged. It does the same thing when I turn back to too high the four-wheel-drive light will stay on until I drive about 10 miles. I pulled the vacuum lines off both solenoids and both bottom tubes have really good suction.I pulled the vacuum lines off the front differential and I have no suction no matter which gear. I tested the voltage from the wires that feed into the solenoids, and both of them are getting 11.8. when the truck is off I can manually move the actuator on the front differential. When is running I can't move it. I have checked all the fuses and they're all good. I believe there's a four-wheel drive relay switch that I should hear when switching into 4 high. I can't seem to find it and I never hear it click.

At first I was thinking bad solenoids, but now I'm thinking maybe it's a relay switch. I don't really have money to throw at random parts I need to narrow it down. I'm new to wrenching but have all the tools I need. Can any of you guys out there help me please?

 

Also I forgot to add, I pulled the 4 wheel drive switch out of the dash and check to make sure the wire harness was plugged In securely. The light in the switch does not work but I'm thinking the bulb is probably just burnt oh, I see that's a common problem with these trucks.

 

did you watch this one ?

 

Yup. The part in the video where he says go ground on selenoidft feed then positive to battery, has me stumped as well. The relay is supposed to break ground depending on mode your in, but I get 12v both sides, no matter what.

 

is there any power at the switch?

 

I I didn't bother to check that, because eventually the light in the instrument cluster comes on. If I didn't have power at the switch I would assume that light wouldn't come on at all.

 

Got stuck again today...

If I can't figure this out soon, I might just buy this posi-lok thing I been reading up on.

 

1. Does shift motor shift transfer case?
2. Is shift fork intact and operable?

If and only if both of those things are okay, then vacuum to the front end is the problem.

Jack up passenger front wheel
With truck off, manually engage axle by moving shift actuator by hand. May need to rotate tire slightly to occur.

​​​​​​Disconnect vacuum lines from front actuator so it stays there.

Your front end will stay connected and you can leave it that way for forever if you like. And just shifting from 2-wheel to 4 wheel drive with the transfer case if that works. All you lose is like 2 miles per gallon having the front differential and driveshaft turning all the time. It will stay that way.

 

I I am not sure of the answers to your first two questions, nor am I even sure how to test them. I'm going to try what you said to put it in full-time 4 wheel tonight when I get home from work.thank you for the suggestion I'll let you know how I make out.

 

I agree, vacuum or lack of is the most likely issue here. check out my picture gallery, as I have some pics posted there of the vacuum components of the 4x4 system. I have heard more than once that the vacuum lines from the firewall solenoids to the actuator can leak vacuum, thus no action at the actuator. also there may be a leak at the reservoir which is in the right front fender.