Normal operation applies regulated disengagement vacuum of 5.8-7.3 in-Hg for 15 seconds and then drops to 0 in-Hg. I assume you are waiting more than a minute before switching from 4x4 to 2x4. I am not sure the 4x4 module is programmed to allow fast switching back and forth.

Griz

 

Griz, No I did not wait for any amount of time to speak of. I will try this tonight after work and see. I do feel what seems to be the solenoid energizing though. I'll give some feedback later. I'll look through the threads and try to find the one on the vacuum wiring harness to see what lead is energized and when and test with a meter to check module output. Thanks.

 

Ok, so I had a chncse to recheck the vacuum with your suggestion Griz and it didn't seem to make a difference. With that in mind would you lean towards the solenoid? Have you ever heard of a module acting up in this way?

 

To tell you the truth...I haven't seen a 4x4 module go bad but if the solenoid you are getting from the wrecking yard isn't too expensive I would try that first. New solenoids cost around $75...not cheap. Have you removed the electrical connector from the solenoid yet? If not I would remove it and inspect the wiring connector/pins and reset the connector. Then retest. On mine the solenoid worked as described...45 second pulse of 10+ in-Hg and then returns to 0 in-Hg to lock and a 15 second pulse of 5-7 in-Hg to unlock then returns to 0 in-Hg. If that isn't working correctly I would replace that first. I don't have the wiring diagram to tell you what the signals are coming from the 4x4 module. I can imagine the 4x4 module is more expensive than the solenoid...lots. If it were me and the 4x4 module wasn't sending the correct signals to the solenoid and everything else in the 4x4 system worked. I would either just manually lock the factory hubs when needed or replace them with Warn or Mile Marker hubs. Just my two cents.

Griz

 

You don't want to be messing with the 4x4 module - on a 99-01 truck that's called the GEM (Genric Electronics Module). On an 02 and later, it's a specific 4WD control module.

The solenoid has two control coils in it, so you should check the resistance of each coil. They should be between 45 and 55 ohms. It's likely that the unlock coil on the solenoid has burnt out (and will show infinite resistance - open circuit).

 

Good info klhansen...do you know which contact pins go to which coil?

Griz

 

I checked the pins on the 4x4 solenoid today on my truck. Pin #2 is the common pin. I had 45 ohms between Pin #2 and #1. And a little higher between Pin #2 and #3.

Griz

 

It turns out that the vacuum solenoid problem was self inflicted. Being curious to how it was built I had taken the white cover off of the top a few days ago. Inside there is a white foam piece and between it and the disengage port is a small disc acting like a check i guess. Apparently I had it out of position when reassembly leaving it wide open and causing a vacuum leak. I also checked the resistance and found 49 ohms between pins 1 & 2 and had 62 ohms between 2 & 3. I appreciate the help but do apologize for this type of problem. By the way the best price for that part in my area was $88 ranging up to $98.:shinner:

 

Guzzle O-Ring has them for $74.22 if you still need one. Here is the link: Replacement O-rings for Ford Diesel Engines

Griz

 

Better at Tousley or:

TascaParts.com

 

Axle seal was the culprit. I didn't replace the u-joint while I was in there because it was fine. Curious how long I can expect the axle u-joint to last. Truck only has 81k. Thanks for the help from everyone that replied.