To test the vacuum pump, turn on the ignition but do not start the engine. The pump should run, slow down and stop. If it does this, you do not have any leaks and the vacuum pump is O.K. If it runs and continues to run, then pull the vacuum line off the pump. Put your finger over the inlet on the pump and if the pump stops, you have a vacuum leak that you need to find but the pump is O.K. If putting your finger over the inlet does not stop the pump, there may be cracks in the housing, or other problems with the pump that this article does not covers. If the pump does not run even with the inlet hose disconnected, you have the problem that I had. First, I swapped pumps with my son's ZR1 to make sure that his pump ran on my car and my pump did not run on his car (everyone should have two ZR1's as it makes fixing problems easier and if you don't, make friends with someone else who has one). This is necessary to check that you are getting power to the motor. You could use a volt-ohm meter but I like to see it actually work.

My pump would not run and new ones were going from $220 up. I figured I had nothing to lose by trying to fix mine, since it did not work. An ohm meter check on the two connections showed that the circuit had a discontinuity somewhere. I pried up the top (good design - repairable - it is a snap-in rubber seal). When I checked the continuity, I found that I was having trouble on the board under the goo. I probed through the goo with a needle and while messing around I got continuity but did not have to fix anything as it fixed itself. I put the vacuum pump back on the car but it still did not work so I had to take it off again. I grabbed the plastic housing enclosing the motor and pulled. (It is a snap-on, too! Gee whiz, is GM finally making things easy to repair? I doubt it; it must just cost less to make this way). Well, the motor casing was crimped on. (There goes the GM Mr. Nice Guy theory, they used to use bolts not crimps.) Afterthought! I should have grabbed the hardened steel shaft that sticks out and turned it with pliers as they will not mar the hardened shaft and it may have got it unstuck enough to wear in. The points were OK!

I tried making something that would pull the crimp out but could not get anything strong enough in there. I noticed that the crimps formed an inclined plane and so I put the vacuum pump in a wooden vice and got out my channel locks. I twisted the motor casing back and forth until it was able to turn past the slots. Don't crush it- if it starts to crush, move your channel locks a quarter turn to get over the magnets; you do not have to squeeze hard. The case will then come up. There is a spring steel washer that fell but caught on the magnetic core. The hardened steel shaft has a bushing on it that I twisted and moved up and down the shaft to clean the crust off of the shaft. The center shaft I rotated to make sure that it turned freely. Put the spring steel washer back on the shaft and put the case on. It is kind of tight so I did not have to crimp it to test it. I put it back in the car and it ran fine but I still had a bad vacuum leak to fix.