How to vacuum test secondary throttle actuator system

[KJL]

I have the plenum removed and thought it would be a good time to check the secondary vacuum actuators. I have a hand vacuum pump I use to check things out on my 72. With plenum removed, where should pump be connected and what lines should be plugged? There are lines to a vacuum pump, sensor (mounted under plenum) and a line that goes to the plenum and connects to the solenoid (not sure what this is for other than solenoid activation?).

Thanks!!

[XfireZ51]

I would start by checking at the Diff MAP Sensor under the ECM. See if the line connecting to it holds vacuum.

[KJL]

I checked at the map sensor and it did not hold vacuum. Not sure if all lines need to be connected and solenoid to be energized for that to work.

[scottfab]

Originally Posted by KJL

I have the plenum removed and thought it would be a good time to check the secondary vacuum actuators. I have a hand vacuum pump I use to check things out on my 72. With plenum removed, where should pump be connected and what lines should be plugged? There are lines to a vacuum pump, sensor (mounted under plenum) and a line that goes to the plenum and connects to the solenoid (not sure what this is for other than solenoid activation?).

Thanks!!

I'd go straight to the hose on each actuator. Test one at a time for smooth non sticking action and no leak down. If you have problems here there's no real advantage to moving to other tests.

[RICHARD TILL]

Did you try to pull a vacuum on the sensor itself or on the line that attaches to the sensor? I have my plenum off now for an injector change and secondary repair. I needed alternator repair, injectors, one coil, vacuum pump and a sec. port throttle solenoid. Maybe it`ll roar back to life next week.

[KJL]

Good luck-
I suspect to test it correctly, I will need to rig up some tubing to connect to all of the vacuum sources and electronically activate the solenoid in order to see if the system functions properly. I may try to post this question in the Corvette Forum to see if I get any bites there as well.

[scottfab]

Originally Posted by KJL

Good luck-
I suspect to test it correctly, I will need to rig up some tubing to connect to all of the vacuum sources and electronically activate the solenoid in order to see if the system functions properly. I may try to post this question in the Corvette Forum to see if I get any bites there as well.

I'd go straight to the hose on each actuator. Test one at a time for smooth non sticking action and no leak down. If you have problems here there's no real advantage to moving to other tests.

[RICHARD TILL]

i checked my actuators by hooking a 6 foot vacuum hose to the vacuum pump on the car. i hooked an alternate power source to the pump and then pinched the line off until i could get it hooked to each of them. the pump ran for a second and then stopped. thats when i waited about 15 minutes to see if the pump restarted. it didn`t so i assumed i didn`t have a leakdown. there are two vacuum lines hooked to the secondary port throttle solenoid. they both unplug together. i took a small piece of copper tubing and stuck it in the hose from the pump. i stuck that line into the vacuum line going to the actuators. another 15 minute test and it passed. no leakdown and worked smoothly. my problem was vacuum leaking thru the solenoid. it can be tested by applying 5-6 volts.