I have read alot of post on here but am still at a loss. I have a 99 f150 5.4 automatic. The four wheel drive is the twist **** on the dash, no manual lockers all internal. So here's the problem......shift into neutral turn **** from 2wd to 4h and the light on the dash comes on saying 4h. Nothing truck doesn't engage it's not in 4h but if you put the truck back into neutral and try to turn **** back to 2wd light doesn't go back out. So here what's next light on dash says 4h and the truck is still in 2wd and it will say that way for 1 to 3 days. Then at some point I will get in the truck during that time period and start it and back out the driveway and the tire bind on the asphalt. Whala!!!! 4h!!!! Put the truck in neutral and turn **** to 2wd and you can hear it go back to 2wd. Then if you were to immediately try to put it back to 4h it will start the same long drawn out process again. I have read post did all sorts of things tested vacuum replaced obvious dry rotted vacuum lines. But in the end I'm at a loss. It work but seems like it work on it own time. So my question anyone know what is causing this so I can replace the problem? Some advice would be greatly appreciated. Thanks in advance.

 

Check the vac lines. They like to crack between the battery box and firewall. One line is Pink, the other is Blue.

 

That's what I thought to but the fact that the 4x4 eventually starts working just long enough for it to engage and then disengage is what makes me confused as to the problem.

 

The relay on the firewall routes vacuum to the actuator down on the front axle.
It must work or you donot get front engagement.
Check it out.
Setting in the truck with the window open you should be able to hear it engage and disengage.
Shift on the 'fly' does not need to be in neutral or even stopped like 4L needs to be.
Good luck.

 

I understand that but I don't think that's the problem. It's the fact that it does work but only when it wants to like I said in my previous post. As far as shift it while in neutral that's just the way I was brought up. Figure you have less chance to break something shifting while stopped versus moving down the road.

 

You have a bad GEM module. Mine did the same thing. Replaced shift motor, solenoids, even rebuilt the transfer case. You'll need to pull the gem out to get the program and serial number off it. From Ford the GEM is $600. Then to install and program is $150. I found a used 1 for $150 with a matching serial number. But first things first, The cause of this is a leaking front windshield. I had mine pulled and resealed at a window shop for about $80..

Also you need to be slightly moving for 4h. This is because there it has a electromagnet in the planetary to help lock in correctly without causing added wear on the driveline. 4L is a different story.

 

So your sure about the GEM? Cause I'm positive I don't have a leaking windshield. Whereis the GEM located at? Is there a way to test it?

 

It could be quite a few things, it's up to you to eliminate the possibilities. So far you haven't done nothing. But yes, there's a very good chance it's the GEM. It's very hard to tell if your windshield is leaking. What you do is disconnect the GEM and inspect blades and connector socket for corrosion.

BTW, - These trucks DO NOT have to moving for 4WD to engage. They can be, but it isn't necessary. I have one up on blocks now that engages just fine in park.

 

thank u I thought the same thing that they do not have to be moving to shift. Do you know where the gem is located?

 

If you search GEM in this forum only, you'll find some great pics of it, diagrams and how to remove. User JMC and I have posted many times on this.

 

Yea, there's allot of info on the GEM, to much to post here.

 

Ok so I pulled the GEM out boy was that fun! The GEM didnt look like it was bad no coorosion on it but I sprayed out the terminals with electric circete board cleaner for good measure. It didn't work truck did the same thing again light says 4h and stuck there but truck isin 2wd. I go under the truck with it running. Now with it in "4h" I have vacuum to the actuator on the blue 4x4 line to the actuator. Actuator was sucked in. No vacuum on pink 2wd line to actuator. Hooked up vacuum tester straight to the actuator on the 2wd side and pumped it up. Slowly the vacuum on the 2wd side of the actuator started to fall to zero. So does that mean the actuator motor on the axle is bad? Or no? Also through all the testing of the actuator the front drive shaft was not turning don't know if that matters being the truck isn't enen in 4x4 even though the dash says it does. Any ideas? Thanks

 

It sounds like its stuck. They go in to dealership all the time stuck like that from what I hear. You have to work it free. It's not a motor. The pin gets stuck. With each pump the pin should move a little. Here's some pics of working the actuator.





Once you get it to move with the vac tool, lube it up w/dry lube.

It might be a bad acutator, but it's usually not the case. Just make sure the pin isn't hung up and that it can indeed move freely. Pry a little bit on the lever there in pic, - it shouldn't take much. If you have a hard time after prying a bit, then it's stuck. If it moves fairly easily, then the diaphragms gone in the actuator.

 

So there was no white water marks at the GEM? Your lucky, those are pricey.

 

If your talking bout the pin as far as the piece with the rubber boot around it then no it's not stuck. It move just fine. But like I said when I put the vacuum pump on the 2wd side the vacuum leaked back out almost immediatly. So if not pin the diaphram. Like u said. I tryed to get the actuator out but couldn't. Took off the E clip from under the boot, but the actuator is like welded into that bracket it sits in. Any trick to removing it? I didn't want to beat it to death if it's not broken. But I would like to get it out to examine it closer and maybe determine if it is the problem. Nope GEM had no water marks on it clean as a whistle. But sprayed it out just in case.