my four wheel drive is working intermittenly. i heard to test the vacuum system you can cycle the vents and if there was a leak it would stay on defrost.??? the vents are working properly. i can hear the vacuum pupm working on the passenger fender well. however the 4wheel drive seems to work off and on. this morning it didnt then i drove for 15 miles and it worked. i have the hubs in auto. the indicator light comes on and off on the dash when i cycle the switch. anyone have ideas, is my 4x4 solenoid in question.??

 

Most likely a vacuum leak...It could be anywhere downstream of the PVH solenoid...ie: lines, inner axle seal, outer locking hub o-ring. Your best course of action is to borrow or buy a hand held vacuum pump like a MityVac. Then start tracking the leak down.

 

How are you determining whether or not the 4X4 is working? Is it just by the dash light, or are you losing traction in the front?

 

I have the exact same issue in my 03 F250. Started happening a couple months ago. 4x4 would work intermittently, losing traction in the front.

I've been running with my hubs manually locked for the time being and have no more 4x4 issues so I believe it to be a vacuum leak. I plan to track it down this summer.

 

Got mine fixed! Crappy Dorman o-ring.

I locally sourced some -152 Buna-n o-rings....$2.51 for both Swapped them with the Dorman....4x4 again baby!

I measured the diameter of the new o-ring, .102, right as it should be, against the Dorman that's been in for a year. .092. I knew something was up when the locking hub was pretty easy to remove from the hub. When I installed the new, I had to tap them in with a dead blow.

 

Interesting what you will find when playing around with these trucks and the aftermarket, isn't it?

 

But come on man....how hard should that be? It's an o-ring for crying out loud. But I suppose if you make a product with 10% less (or more) material, you can get some profitability.

 

How much could that save them, 100 dollars per 100,000 units?

It's just stupid.

 

The MityVac has been a rather expensive but useful investment for me. It can be used for a slew of things

 

The ginormous picture of the one I bought was around $30 on sale @ Harbor Freight.....took almost 2 weeks for it to arrive though.