4wd switch on the fly - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 2 (permalink) Old 02-08-2019, 03:17 AM Thread Starter
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4wd switch on the fly

When I select 4wd using the switch on the dash, with hubs unlocked, they engage and then disengage again within about a minute. The vacuum pump reaches its set pressure and switches off even though the 4wd has disengaged again. Any pointers would be much appreciated
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post #2 of 2 (permalink) Old 02-11-2019, 10:56 PM
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I suppose if there was a leak at the pump or reservoir the pump would keep running. Perhaps you have an issue with the solenoid on the inner fender passenger side near vacuum pump. I had an issue with mine on my 99 and replaced it with good results. I don’t recall how but I remember there being a way to test the solenoid with multimeter to see if it’s shot. The fact that they engage to me means there is no leak at the hubs.
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