98 Navigator will not engage 4X4 front axle

[bhickmott]

Hi Guys

Any suggestions for my 98 Navigator that will not engage the front axle for 4 wheel drive in either A4WD, 4X4 or Low Range ?

The diaphram unit on the front axle works fine. If you connect vacuum to either side of the diaphram it will engage or disengage the the 4 front axle correctly. The problem is that vacuum does not shut off and is always applied to the disengage side of the diaphram. Traced the vacuum lines back to two electrically controlled vacuum solenoids on the firewall and found that 12 volts is always applied to the disengage solenoid regardless of where the switch on the dash is positioned (2WD, A4WD, 4X4, Low). The lights on the dash do change properly and you can hear relays clicking as you move the dash switch, but the disengage solenoid always receives 12 volts.

Does the power for the solenoids come directly from the Generic Electronic Module (GEM) ? Is there an easy way to diagnose ? Does anyone make a cheap replacement module ?

Bill Hickmott
617 803 4104

 

[bhickmott]

Problem turned out to be a defective vacuum solenoid. There are 2 solenoids mounted a common bracket on the firewall to the left of the power distribution area and right behind the battery. The right solenoid (E8AE-9H465-AA) controls the vacuum to the return side of axle engagement diaphram. The left solenoid (E8AE-9H465-BA) controls the vacuum to the activation side of the axle engagement diaphram. The right solenoid was stuck in the open position which allowed full vacuum to the return side of diaphram at all times. I took it out and applied WD40 with 100 psi of air coupled with a few good "raps" on the bench and it did begin to function again, but it still had a slight leak in the off position. The 4X4 now works fine even with the slight leak, but I have ordered a replacement solenoid ($44.00) to be sure.