Stumblin Bumblin Z

[QB93Z]

Originally Posted by 1963korvette

Got home last night and was able to find pressure sensor easy enough. unfortunetly I spent the better part of 3 hours pouring over the shop manual trying to find out how to check to see if it was working right. can someone tell me. The book did say it would throw a code 56 I believe. I have no codes. Very fustrating.

You are right, I looked this morning and I could not find a way to test the Differential Vacuum Sensor. I remembered wrong, I thought I had tested it back when I was having the problem you are having.

When I was having a problem with similar symptoms to what you describe, the issue turned out to be multiple failures. The vacuum pump had failed and the check valve in the secondary vacuum lines had failed. I replaced the check valve and the pump. The replacement check valve failled immediately, so I had to do all the troubleshooting over again.

Get back to basics. With the Power Key off, does the car drive properly at full throttle (understanding that it will have less power)?

Next to the alternator, there should be a vacuum line that runs from the vacuum pump to under the plenum. There should be a disconnect fitting in that line. With the engine off, disconnect the line and connect a vacuum gage to the pump side and run the pump. Do you get a strong vacuum that holds when the pump stops?

Connect the MightyVac to the system side of the disconnect fitting and pull a vacuum. Does the vacuum hold?

Jim