Electric Vacuum Pump

[DMcV]

We had some snow a few days ago, went to use 4x4 and it wouldn't engage.
So today I did some research (online) to find it may be my electric Vacuum Pump.
Test = change heater settings to see if air would blow from dash or floor other than defrost vents. Results = would not stay on dash or floor, it would change back and forth on it's own. I checked all hoses and found only one on the passenger side split at the hub conection. Repaired that now found there is little to none vacuum at the hubs, pulled the hose at the vacuum pump and found very little vac pressure there. Now vac pump runs continually but will stop if I put a finger over the inlet (on the pump).
Question should the vacuum pressure at the pump and hubs be quite noticeable ??.... or does it relay on the accumulation tank to provide enough vacuum ?? Please help.... I don't want to go and by a new vac pump unless it's another problem.
Thank you in advance.
Dennis

 

[OLDBULL8]

1st thing I would do is get a vacuum gage and hook it to the pump suction and see how much vacuum it pulls, a perfect vacuum is 29Hg. Then hookup the line(s) check vacuum then. I think you have bad vac hose(s) somewhere, if the pump shuts off with your finger over the suction.

 

[Double-S-Diesel]

sounds like a bad hose, if the pump is shutting off.
usual culprit is the vac hub seloniod on the pass fender well

 

[DMcV]

Update

OK.... I bought a vac tester and found I have 17 Hg at the pump.
Seems low from what OLDBULL8 replied. From there on I tested the tank by taking off the hoses at the bottom of the solenoid, plugged the heater one and stuck the vac test into the other, tank built up vacuum to more than 15 Hg and I quit there because it was not hooked to the solenoid shut off.
I highley suspect it's the PVH (pulse vacuum hublock solenoid), as there is no vacuum after it at any hoses and it does not make any noise when switching from 2WD to 4WD (key on) .
Any other input would be appreciated.
Dennis

 

[OLDBULL8]

Repaired that now found there is little to none vacuum at the hubs, pulled the hose at the vacuum pump and found very little vac pressure there. Now vac pump runs continually but will stop if I put a finger over the inlet (on the pump

The vac pump stops with your finger over the inlet, that tells me the pump is good enough to trigger the shut off switch. It's possible that the O'ring(s) in the hub(s) are shot if the vacuum goes to 0 Hg.

Go here for the front hubs and more, says 2002 but it's the same for 2000 http://www.guzzle7pt3.com/maint.php

 

[DMcV]

On going problem

I have one more question........
If the FWD switch on the dash is 'off ' shouldn't the two hose conections on the bottom of the PVH (pulse vacuum hublock solenoid) not allow any air to passage ? To help make my question clearer , the vac pump keeps cycling, on & off, even when hoses to hubs are off & plugged, the hoses maintain vacuum and hold (other test) , so no leaks in hoses... But I can blow or suck air when I attach a hose to the bottom fittings of the PVH which seems to pass air eaisily in or out.... should it pass air ? This seems to be allowing vacuum to be lost. Help
This is a NEW PVH from the dealer.
Dennis

 

[Double-S-Diesel]

im not shure on ther pvh most I have a plugged off.
try this does the vac line to the hubs hold vac, you may have a hub seal that is leaking.
from what I know about the auto hubs they use so much for so long to lock, them so much for so long to unlock.

 

[DMcV]

Double-S-Diesel.........thanks for your post,

I have checked the PVH for function , and it does the pulse vacuum to ingage and disengage correctly. However, I have no way to check hubs to see if the hold vacuum to see if the seals are good or not. I have plugged off the hoses at the hub end and the PHV seems to be allowing air to pass , thus loosing vacuum even when the dash switch is 'off '.
So my concern is ..... is the dealer new PHV faulty or is it supposed to allow vacuum to leak ?
I guess I'm just lazy and want something that is supposed to work and it doesn't.
Dennis

 

[timpsd02]

Not sure if you fixed your problem yet. I had a similar problem with mine. I only lost vac when i engaged 4x4 on dash. I thought the problem was with the hubs or lines to the hubs. Turns out that the valve itself had a small crack that only lost vac in 4x4. replaced entire valve and worked fine.

 

[OLDBULL8]

Why don't you start a new thread. It gets confusing attaching a post to an old old thread.

Go into your post on Edit and copy it, then delete the double posts. Then start a new thread about your vac pump.

Welcome to the OB. Lots of info here.

 

[Donald 26]

Thank You oldbull8

As stated my fist post thanks for your help