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Ok, now I am getting really confused. You said earlier you tested the pull down for the headlight and found it leaking vacuum.
I realized that I had not blocked off the black/white hose to the wiper relay since removing it for testing. Once I clamped it I was able to pull vacuum but it slowly goes from 20.0 HG back to 0.0 HG after about 5 or 6 seconds.
When you start and run the engine, it makes diagnosing issues much more difficult. Do your tests with your vacuum gun, engine off. If the headlight pull down is indeed the culprit, you would see a noticeable difference when you test the control circuit with the pull down bypassed and when it's not. This is the test I'm most interested in.
Hi Dave, sorry for the confusion, I thought I had previously provided the test results for the separate wiper and headlight control circuits. But to be more up-to-date with readings I ran the tests again this morning.
Headlight Control Circuit – I couldn’t reach the “T” under the dash to separate the vacuum source to the headlight and wiper control circuits. So I isolated the headlight circuit for testing by clamping the black hose at the check valve under the hood that feeds vacuum through the firewall. I also “connected” the two hoses that attach to the by-pass the headlight manual override pull down switch/valve (I had already determined it was leaking and I have a new one coming from Willcox). I then disconnected the wiper control vacuum source hose at the solenoid to pull vacuum with my vacuum gun. Results: It took 15 minutes 35 seconds to drop from the initial 20.0” HG to 19.0” HG. I’m thinking that’s acceptable, No?
Wiper Control Circuit – Now knowing the results for the headlight circuit, if the wiper test results were worse I thought I’d be able to conclude that the wiper control circuit would be my problem area. So to conduct this test, and to be consistent with the previous test, I connected the two hoses going to the wiper manual override pull down switch/valve to by-pass it. I also reconnected the vacuum source hose back up to the wiper solenoid. I then applied vacuum to the black vacuum source hose at the check valve in the engine compartment. Results: It took 17:40 to drop from 20.0” HG to 19.0” HG. That also seemed okay to me.
Just for kicks I reran the wiper test with the “known good” vacuum manual override pull down switch installed. Results: It took 18:01 to drop from 20.0” HG to 19.0” HG. I guess it confirms that switch is working properly.
If what I’ve done makes sense, it appears my problem is not with either control circuits. Your thoughts?
You are correct. In a perfect corvette vacuum world, the vacuum system would hold vacuum for quite a while if it had no leaks.
I would say the leak is probably under the dash. You have corrected the open vent, and tested the top of the relays, so that leaves the dash components. If it were me, I would follow my suggestion to block off each side separately at the "T" 3 way between the check valve, headlight switch, and the solenoid. Then test each side. That will give you which side the leak is on. Wiper door side, probably the solenoid is dirty inside, preventing a good seal. Headlight side, probably the vacuum valve on top of the switch is the culprit. These can all be tested in the car if you need to.
You can follow Willcox's schematic below. The "T" is located behind the speedometer high under the dash. It's normally reachable lying on one's back. I have also accessed the hoses by reaching up under the dash and following the hose through the firewall.
If I was to cap off port C on the check valve, would that effectively eliminate the wipers from the vacuum system?
That would eliminate the control circuit to the wiper door system. However, it would also eliminate the control circuit to the headlights as both control circuits feed off the same "C" port.
That would eliminate the control circuit to the wiper door system. However, it would also eliminate the control circuit to the headlights as both control circuits feed off the same "C" port.
What exactly are you trying to accomplish?
I'm still in the process of figuring out all the vacuum hoses and I was thinking that it might make it easier if I just eliminated the wiper portion of the system as this car will most likely never be driven in the rain.
Ok, now I am getting really confused. You said earlier you tested the pull down for the headlight and found it leaking vacuum.
When you start and run the engine, it makes diagnosing issues much more difficult. Do your tests with your vacuum gun, engine off. If the headlight pull down is indeed the culprit, you would see a noticeable difference when you test the control circuit with the pull down bypassed and when it's not. This is the test I'm most interested in.
Dave, because you've been very helpful on my wiper issue, I wanted to provide you with an update. After going through all of steps you provided (thank you very much) I still couldn't pinpoint the problem. Although it did help me identify a number of parts that were replaced. So I started over thinking I missed something or did it incorrectly. I know you said not to use engine vacuum, but that was the only way I could find the final problem part, because it took so long for the vacuum to drop.
Long story short, I've got what I believe is a leaking seam in my vacuum tank. When the tank is bypassed the problem goes away. But after reviewing a thread on how to fix a leaking tank, I've determined that the process to get it out of the car to be worked on will take a ton of work, so I've put it off until this winter when the car will be in the garage resting through our usually very cold Michigan winters. Plus, I wanted to put it on the road this summer to enjoy it while I can.
Thanks again for all the help you've provided on this wiper issue, as well as the headlights!
