ESOF Diagnosis Help....

[tallyF350]

When I switch turn my 4x4 switch in the truck (ESOF) my defrost comes on, so after reading all the threads I went and got a vacuum pump.
I have checked:
both lines going from the HUB to the frame rail and they held 10lbs of vacuum.
I went under the hood and pulled the elbow apart near the vacuum canister and hooked the pump onto the line going down to the T near the passenger side of the engine, and it held 10lbs of vacuum. see pic

What do I check next?

And yes I know I can switch to Warn....

[ZMANN]

i would check the esof valve and see if it's commanding vac for the short duration after you select 4x4 .. they can leak internally

ps you have Warns LOL just OEM Warns

[tallyF350]

Originally Posted by ZMANN

i would check the esof valve and see if it's commanding vac for the short duration after you select 4x4 .. they can leak internally

ps you have Warns LOL just OEM Warns

LOL on the warn hub....Thanks for the input

Here is the valve..is there a way to test it? I tested all the lines around it and they all held vacuum. but i think the leak has to do with this as well....

[ZMANN]

i hooked the gauge up and flip the 4x4 switch while the truck is running and ran back to see if I had a reading on the side going to the hubs it will vary and only runs for about 1/2 a minute but you should see it hold a certain vac ,, like 10 ish IIRC

[tallyF350]

I think this is it. It won't hold a vac.....and the spongey thing inside the cover is dry rotted and shot....found one on eBay for $60...I will post the results...

[tallyF350]

Originally Posted by tallyF350

This was it!!! New one came in today, and it fixed the vacuum leak....

[ZMANN]

Nice ..............