I tried searching. My 4WD is not engaging and the light does not come on. How could I check/test the vac system on my truck? I have inspected here and there. Is there something else I should be checking?

Is the vac motor supposed to move if you try to turn it? I looked in the Haynes manual and it looks like it just slides in and should be able to rotate.

Where do I start?

 

Are you having problems with cruise or the vents when you change from say floor to panel?
If so, I would look at the main hose from the vac pump.
If not, I would look at the individual vac lines from the front diff all the way to the transfer case. This will include the firewall portion as well.

 

X2

i had them come off of the main line at the vacuum pump and at the T on the firewall

 

Im not sure if your truck has the same vacuum operated axle control that my 96 had. But all it takes is one time for a no- f.w.d. situation to happen when you really need it. It removed my vacuum system and put in a 4x4 cable operated system. $200. but, $2,000,000 worth of piece of mind knowing your going to have 4.w.d. Frank

 

I have looked everywhere for a cable system and no luck. One place (cant remember what it was) does not carry them. WhERE did you get yours???

Thanks

 

Wow. My vents act funny and my cruise has not worked since I have owned the truck. Where exactly is the vac pump? I will try my Haynes manual. Thanks

 

I broke my vac line [unknowingly] that ran to the firewall while changing my fuel filter. I bought a long plug, cut the end off, and made a nice rubber splice out of it. Check all around for breaks in any of the hard plastic lines running on the driver side of your engine. Definately a vac leak though...

 

The vacuum pump is between the power steering pump and the front of the motor. The vacuum pump bolts to the motor and is driven by a gear. Then drives the powersteering pump. Follow the rubber hose from the pump up to the firewall and beyond. More than likely you will find the rubber hose has dry rotted. I saw yesterday while tracking down my wait to start wire for my remote start that I need to replace my hoses as well before I have issues.

 

I found the t-connectors and such on the firewall. did not see anything disconnected but may try replacing some of the rubber parts.
Is there a good way to test for a leak or is it just by eye?

 

Pretty much have to just track it down from the vacuum source.
By the way, do you see spots of oil under your truck like your power steering pump is leaking? If so, it's probably the vac pump. If it gets bad enough, you will lose vacuum as well.

 

Always fun to work under a noisy cummins, but do you have VAC at the connector on the Transfer case? From there we'll know what direction to go.

 

I do not have spots but I have been frustrated with a "leaking" p/s pump. There is always oil on it that does not make it to the ground, just all over the undercarriage. Where is the oil coming from?? The p/s fluid level seems to stay at the same level. What is the next step I should take? By the way, thanks for all the help.

 

With the engine running pull off the two vaccum lines that attach to the back pass side of the front axle to check for vaccum. If there is vaccum, then your lines are ok. You then need to remove the cover on the back pass side of the front axle to check the "central axle disconnect" (I think thats' what it's called). There is a splined "tube" like device in there that slides back/forth to engauge/disengauge the front axles (4x4). Make sure this moves freely and if you want to check further, jack the front up and you should be able to slide it to engauge/disengauge. May want to add some gear oil if it's low as well. If this goes out your best best would be to install a manual engauge system as noted above. Hope this helps.

 

I too thought it was my PS pump. It is actually the vacuum pump. Click here.
The leak is actually engine oil getting past the bad seal in the vacuum pump. I recently did the repair on mine and it was a breeze. Click here for a short write up I did with a couple of pics.

 

The vacuum pump is on the drivers side of the engine, underneath the injection pump. The power steering pump and vacuum pump are on a common shaft. Here is what to look for under the hood, the PS pump is on the right, vac pump on the left: