Engine/Transmission (1994 - 1998) Vacuum pump suction

[JC Buck]

My vacuum hoses have been broken since I purchased my truck 4 or 5 months ago. I've recently started replacing lines, mainly in an attempt to recover my vent selector. My question: How much suction should the vacuum pump produce? My dash vents now work intermittently and I'm trying to figure out whether I still have a leak somewhere or if my pump might be too weak. If I put my finger over the line coming off the vacuum pump I can feel suction but it certainly doesn't feel like the skin is about to be sucked from my finger tip. Does this sound about right?

As a side note, for other CA owners, I removed my egr crossover tube while inspecting the egr diaphragm and found a lot of flaking rust accumulated in the crossover tube where it connects to the diaphragm unit (presumably from condensation). My egr valve has not been opening because of the vacuum leak, and thank goodness.

 

[hsmith]

I have a vacuum gauge on mine, just because there was an extra space. Mine holds steady at 28 inches, but isn't an expensive gauge so could be off a bit. One thing you need to check is for oil contamination from the pump all the way to the selector switch as it can damage the rubber in the switch causing similar problems to yours.

 

[ata]

If your Vacuum pump pulls 14 to 28 inches it's within spec. Put a test guage at the pump and see what you have and then check at the control switch and see if you still have the same reading if not you have a leak.

 

[JC Buck]

Thanks for the help. The pump tested OK so now it's time to find the leak.

 

[SRehberg]

Hsmith brought up a good point as there was a recall with some '96's that left the factory before the inline check valves were std. equipment. I checked my vacuum lines after the recall and found oil residue clear up to the HVAC control and not quite to the servo motors. I blew brake cleaner through all the lines and as a cheap oil catcher, installed a inline metal gas fuel filter immediately after the check valve. It has been in service for some years and no oil has gotten by it. I need to replace it as I can't see the amount of contamination. Just my 2cts