Engine/Transmission (1994 - 1998) Vacuum Reading

[CBrabec]

Does anyone know what the correct amount of pressure I should be reading from the vacuum pump if I put a guage to it? The reason I am asking is because I have a vacuum leak somewhere but can't figure out where to start. First off, it all started when the "BRAKE" light stayed on and I was having troubles stopping (I had all new brakes done about 2 months ago and a new master cylinder was put on when I bought the truck 3 months ago) and then my blower is stuck on the defrost mode even if I turn the dial to lets say the floor. A friend told me to see if my cruise control works which could be another sign of a vacuum leak and the cruise works just fine. I checked all the lines I could find and nothing looks like it came loose or is damaged. The only places I havn't checked yet are under the drives battery and under the dash. I am a newbie to these 12V's so my learning process is just beginning. Any suggestions or help would be greatly appreciated.



Chris

 

[DWeaver]

I do not know what the pump should be pulling on vacuum.

I will suggest that the line between the pump and brake booster should be the place to start testing for leaks.

The few I have worked on usually had the line to the cruise control cracked, sounds like yours is good. Then I would move onto the front axle lines that run to the t-case and the front axle.

Sorry I could not help more.

 

[NIsaacs]

Vacuum varies with elevation, Nebraska is low mostly, so I would say you should have 24 + inches. It is rare for the pump to quit. It is almost always a leak. Check real good around the cowl where the vacuum lines connect. I think the one for the heater runs real close to the exhaust, might be melted.



Nick

 

[mwilson]

If you still have cruise and 4WD then you may have a bad actuator on the heater itself or a bad control head.



You really need a hand held vacuum source to check this out. Also rotate the knob through all positions and see if you might have only lost the panel air. I lost an actuator last winter and thought that I only had defrost. Come to find out I had defrost and floor air, no panel air.

Actuator had a hole in the diaphragm. The one that is responsible for panel air stands on end and the oil from the vacuum pump just lays on that rubber and will after time rot it out.



Mike.

 

[MLee]

22 to 24 inches of vacuum. Do a search your problem sounds like it mine be in the heater controls if thats all you have from the switches.

 

[Missouri Mule]

The vacuum line that goes in the thru the fire wall on the passenger side is close to the the exahuast manifold as was stated earlier. Even if it is not melted it would be a good idea to reroute it ( I ran it over the heater hoses).



I doubt it is a pinced line since it effects the brakes also. When I had trouble with my control selector and it got stuck on defrost vent because of a pinched line under the dash (defrost happens to be the default mode if something happens to vacuum system).



You mite want to check out the vacuum check valve on the brake booster (you should have one on the vacuum pump also).

 

[hsmith]

Or, could be oil contamination from the vacuum pump causing the control, servos, to malfunction. Mine did not come with a check valve at the pump but it was added later.

 

[CBrabec]

Thanks guys for all the advise, I hope to tear into the truck over the weekend to see what I can find.