ESOF vacuum lines on 2008 F250 6.4 have deteriorated and I am in the process of replacing but during diagnosis I noticed that the pump cycles momentarily every few seconds (kicks on and off) even when the vac port is plugged at the pump (eliminating all lines as a potential leak). Does this mean that I have a defective/leaking pump assembly also? I suspect this behavior is not normal.

 

I would agree that the pump is probably shot. If it were me I would spray the pump with windex or something to see if I could figure out where the leak is.

 

Not sure what Windex would do but if it were me, I would hook a vacuum gauge to the pump port, let it build vacuum to shut off and monitor for leakdown. You current plug could be leaking, pump housing cracked etc. Just replaced all lines and upgraded the DeGas bottle. Not a bad job to run the lines unless you have to replace lines going to hubs, that takes a bit longer. Be sure you vac test the lines at the pump when done to make sure you don't have a leak when lines are done.