You've got it backwards. If there IS vacuum at the actuator hose then replace the actuator, because it means the actuator isn't responding to the presence of vacuum. If there is NOT vacuum at the actuator hose, then you'll have to follow the vacuum line back and test for vacuum at every junction or component you run into to see where you start getting vacuum.

 

Perfect clarification, Alloro. Thank you. I will check back and report my findings.

 

First I want to thank all who contributed to my resolving my 4x4 engagement problem, especially Alloro, Denphillips2, and Jennkent5454, and StevenIll. Each of you were integral in assisting in resolving this issue.

You can read my posts and follow the plan of attack. At first I thought this was a t/c motor issue. I replaced the motor and nothing changed. Upon further reading on this site, I was directed to the 4x4 actuator and the vacuum lines connected thereto.

What was most helpful was getting under the truck. I first checked around the actuator, sprayed it with WD-40 to ensure movement. I had a friend get in the truck and change the ESOF switch from 2 to 4wd as I watched the acutator. It would only move one way which led me to believe I had a vacuum issue up the line. To be sure, I began by disconnecting the vacuum lines to the 4x4 actuator. I found that I had vacuum to the red line (4x2), but novacuum from the blue (4x4) If that was the case I was told to move back up the vacuum lines to look for a crack or listen for suction. Part of the difficulty in locating such a crack or leak is both the red and blue lines which come out of the solenoids are protected and hidden in that black flexible conduit so how do you know if there is a problem without pulling it off?

Anyway, I was told to focus on areas near the battery where the solenoids are located due to battery acid and cable movement so I started there and just moved down. I did peel some of the conduit back in an area that looked corroded and suspicious and don't you know, I found it! A hole in the blue (4x4) line! It appears it was due to battery acid. Glegarry Auto Parts in Livonia, MI "gave" me a piece of vacuum line as a Christmas present which I bridged over the cut-out portion. I added a little caulk adhesive to hold it in place and my 4x4 works again! YEAH!!!!!!

Note: As I have always had, my A4wd light still blinks and I don't know why. Perhaps I'll deal with that next spring. BUt 4x4 hi and low are functioning

Thanks again, all. Have a very Merry Christmas and Happy New Year.

 

Thanks for the update Kurt! This thread has helped me understand mine more also. I pulled the battery and it didn't change anything. My 4AWD light come on and was good until I hit about 40mph then it started flashing.

Will your 4WD engage while you are moving, or do you have to be stopped? Mine will only engage while stopped, but it is engaging. Couldn't drive much at all with it because we have no snow and didn't feel like driving out of town to find a dirt road.

Thanks!
Denny

 

Hey Denny, I'm glad it was helpful.

My 4wd works now as it did in the past. I can shift on the fly to 4 hi. Obviously I can only shift into 4 lo from neutral. My A4WD still flashes no matter when I switch it. To me, it's not a big deal right now. I will continue to research it and take a closer look at it next spring when it's warmer. As for now, I have 4 Hi and that makes me smile.

Regarding your issue, from the research I've done, seems to indicate that your issue may be a speed sensor. Alloro seems pretty knowledgable about them so you may want to pick his nugget for info. He has a way of clarifying things nicely.

Good luck and let me know what you find. Happy Holidays

 

Great Thread, and thanks to everyone who post great replies.
My 98 Navigator will not engage either, and I will proceed with all of the above recommendations, EXCEPT.....my switch lights do NOT come on. Could it be simply the switch? If so, how would I check just the switch. can i take the wires on the back of the switch and jump them together to see if the 4wd kicks in?

Thanks in advance, Gabor

 

The lights are controlled by contacts within the shift motor, not the dash switch. Your problem lies with the shift motor, it's connector, or the wiring harness going to it.

 

Alorro, thanks for the quick response!!!
That makes alot of sense, I will proceed to crawl underneath, will post results later.

 

Thank you for this write up as well. I found out the hard way this week that my 4wd wasn't working. I will have to check this out since they are calling for more crap this week.

As for your A4WD light blinking, it might be a bad sensor in the transfer case. I had my 98 in for service and had them change both sensors out. The one sensor was bad so problem solved!

 

Hey Old Truck Nut,

I had a question regarding the A4wd sensor. When I changed the t/c motor I had to take wires from the old and transfer them to the new harness. I believe there were 7 in total coming out of the transfer case: 1 loan tan wire, a set of three off to the left and a set of 3 to the right just below the tan wire. I was curious if you knew are the two sets of 3 wires the sensors you speak of for the a4wd? I may try to get under there again in the spring. How much did it cost, if you don't mind? Thanks for your insight.

 

Thanks for the write-up boys. My 4WD failed me when I needed it most. We had a big blizzard here in SE Wisconsin a few days ago and my wife got stuck at the bottom of our slightly inclined street with her car in about 12-15 inches of snow, at midnight no-less. No plows out......they were waiting out the blizzard. I was going to attempt to pull her up the street and I couldn't even get my truck out of the driveway (large drifts) and I discovered I had no 4WD!

Anyway, I worked on the truck today. I had vacuum from both lines at my 4WD actuator, but no movement from the actuator. I ended up working it by hand and spraying the piston with WD-40 a bunch of times and eventually got it moving somewhat freely. I put things back together and she's engaging into 4WD fine now. If it happens again I will just buy a new actuator, but for now it's working fine.

Thanks again for taking the time to write things up...........very helpful.

 

Sorry for the slow reaponse, but the total cost was $406 (trans shop). That was for tranny & transfer case sevice, drain torque converter, and replace input & output sensors. He said he pulled the t-case motor the replace the sensors. When he tested it, it came up with code P1874 Sensor Power Circuit Failure.
Part # (according to the reciept)
7F293AB Sensor IN
7F293BA Sensor OUT

Hopefully this helps everyone out.

 

For the love of God man don't leave us hanging, what happened with your wife?

 

Oh, hell, he probably forgot about her

 

I didn't want to ramble on unless you guys were interested

The wife and I attempted to get the car up the street back to our house for a couple of hours. Ultimately it sat at the corner, blocking any other cars from coming through (we live in a culdesac). I decided to wait it out in the car until a plow came through, and my wife went to bed. I ended up falling asleep in the car, only to be woken by my neighbor pounding on the window at 4am. At 4:10 am or so the plow came through. We were able to get the car to the plowed area on the connecting street to our culdesac. From there I drove the car back to the hospital where my wife works, parked it in the parking garage, and walked home. I got to bed at 6:15am. My wife woke me up at 9am, thinking the car was still stuck at the bottom of the street. I proceeded to clear the drive (borrowed my neighbors snow blower) and got her back to work at 11am, and then drove myself to work.

It was an evening we won't forget anytime soon...........