croakar

Trying to chase down a vacuum leak. Pulled the line to the intake flap actuator and could not get any vacuum. I checked the line going from the solenoid (intake flap control?) to the manifold (the flappy) and the vacuum was good (I pulled the cap on the manifold and could see the flappy move ever time I pumped the mity vac). This led me to believe the solenoid (flap control) was bad. I pulled the hose going into the top of solenoid and tested the solenoid for vacuum. Zero reading. Do I have a bad solenoid?

P.S. All this was done with the no key in the ignition (not sure if that makes a difference)


Mike
88S4

Lizard928

The solenoid has 3 ports, vacuum, acc, and bleeder port.

Check that you have the ports correct. It is also the same as the boost valve on alot of GMs.

croakar

yes I see all the ports. Vacuum line is on two of them. I am trying to determine if there is supposed to be vaccum at the solenoid. When I pull the vacuum hose going into the solenoid from the check valve and try to create a vaccum at the solenoid I am not able to - trying to see if that is correct.

I tested the solenoid from the flappy valve side and it holds vacuum.

Lizard928

It should hold vacuum with the plug disconnected from 1 of the 3 ports.

dr bob

If you tested the solenoid from the flappy side and it holds vacuum, the flappy is connected to the wrong port.

With the solenoid de-energized, the flappy port should be open to atmosphere. The vacuum-source port should be closed with the solenoid de-energized, and open to the flappy port when energized.

The vacuum source hose runs to the back of the motor and then connects at a rubber cross fitting immediately to the right (in the car, right is right side of the car, passenger side on US cars...) of the brake booster at the firewall. From the booster, a tiny hose goes to a check valve, and the cross fitting is just after the check valve. From that fitting, hoses go to the HVAC system solenoid rack in the center console, and to the vacuum reservoir at the rear of the driver's side wheelwell (hidden by the plastic wheelhouse liner). It's unlkely that you will pull long enough on the MitiVac pump to lower the pressure in the reservoir a lot, if that was part of your diagnostic method. You should see system vacuum on the MitiVac gauge with it connected to that source hose and with the engine running.

croakar

You nailed it Doc - the hoses were on the the wrong ports. I put them on the right ones .... tried the mighty vac and behold we have vacuum right from the fitting near the check valve. The prior owner told me they had gone in and fixed the flappy they must have switched the hoses then.

Now need to trace the slow leak from the black line at the check valve going into the HVAC center console. I also have no vacuum on the white line heading from the heat valve into the center console.