Specs
2002 ford f350 7.3l

Need some assistance with the ESOF not working. I did some pre testing and these are some of the results I have found.
Tester auto body now vacuum pump.

Connecting the tester to the vacuum pump these are results.
Takes 1.5 minutes for the vacuum pump to recycle
Gauge inHg
10 recycle
15 top
Connecting the tester to the inlet and back pressure tested the reservoir. Pumped the tester to
10inHg and this held for 7 minutes with no 4wd engaged. After the 4wd ESOF is engaged the pressure dropped rapidly and was unable to pump the pressure back to 10inHg or any other measurement.

So obviously there is a leak in the 4wd system, so I wanted to see if there are any suggestions?

Thanks

 

My hose fittings that thread into the knuckle were broken. The vacuum hoses were cracked & the seals were bad.

 

First thing would be to plug the lines where they go into the steering knuckle's and see if that fixes the leak. If it does then your leak is in the auto hubs or the big knuckle seal, if not then it is in the line's going down to the hubs...

 

Easiest thing to do is forget about the esof and just manually lock the hubs. That's what I do at least. Mine died in my 2006 F350 years ago.

 

That is the easiest but he still needs to find his Vac leak..

 

Did some further testing today. Put the vac tester in series with the pump and the reservoir. The vac pressure does rebuild and pulsates when driving. Starting point between 10-15 inHg in 2wd (hubs in auto) when I switch to 4high I can hear the defrost kick in and the vac pressure goes to 0 after 15-30 secs pressure rebuilds and the 4wd engages. However it does not stay engaged. I also determined if the HVAC is off the 4wd does operate better but at anytime when I switch between 2/4wd the vacuum pressure drops and takes up to 30 secs to rebuild? Is this possibly the way ford intend this to work? To further troubleshoot I left the truck in 4low when I got underneath it I took the front knuckle u-joints and could rotate the shaft (both left and right knuckles would turn. But the transfer case was locked in.

If it is the HVAC where the leak is happening does anyone know where the vac line comes in to? Is it the vent controls or the blower? Not enthusiast about pulling the dash apart to find out the hose to defrost is not the problem.

 

No. No, it's not.

Can you hold vacuum in the hubs? I have one hub that leaks. Been ignoring it for over a year now, but I really need to get it fixed...

 

Do a search for ESOF problems and start looking through the hundreds of threads.

 

That is the next step to test. Could be a couple of weeks as I am going out of town. I will update the blog after I test the hubs. If anyone else knows please update but what would be a good vacuum pressure in the hub be and should that hold for how long?

 

Its your seals leaking. Common to wear out.

 

if you haven't already figured your issue out, I though this video was pretty insightful back when I was first dealing with a leak on my 6.0...