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James, Ford Technician
Category: Ford
Satisfied Customers: 3630
Experience:  Ford Senior Master Tech, Ford gas and diesel expert, ASE Certified
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99 ford expedition 4wd not engaging think maybe the awd

Customer Question

Customer: 99 ford expedition 4wd not engaging think maybe the awd drive is not either
JA: Thanks. Can you give me any more details about your issue?
Customer: key on engine off if I switch from awd to 4wd vent blows fine, if I shut off key and turn key back on then vent defaults to defrot but if I start truck vent blows fine so I don't know if vacuum problem. When I look at vacuum lines from front axles they only go about 2 feet and go into a plug and there are wires out the other side so maybe those are mini vacuum switches/pumps? snowy day here and I could spin out easily and so don't think front is engaged anytime.
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Submitted: 1 year ago.
Category: Ford
Expert:  James replied 1 year ago.

Hello, if the vents are working fine while the engine is running it has good vacuum. On the front axle is a disconnect solenoid that uses vacuum to engage. The two small solenoids you see on the firewall engage and disengage the 4wd solenoid. If you follow the vacuum lines down to the engine they are known to rot and breAk in this area. Sometimes the solenoid on the axle breaks also from rocks. On a rare occasion the fork that engages 4wd can break and you need a new shift fork assembly.

Expert:  James replied 1 year ago.

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