E.Murray

Took the '68 on its first drive and had a bizarre thing happen. The wiper door opened and closed itself a few times. After paying attention, it opens when I let off the throttle and closes once I get back on it. Seems like high engine vacuum opens it and low vacuum closes it. Is it a bad actuator?

Easy Mike

Check the in-line white plastic filter and the metal valve on the vacuum supply line. Either can leak.

Kevin68

Maybe, but I'd look for a leak in one of the lines or connections first. Could also be a bad vacuum relay or check valve. As a first check and because it happens fast, rev the engine to build up vacuum, then shut it off and listen for a hiss.

C3 Stroker

Had the same thing happening with mine.......found the problem here.....https://www.corvetteforum.com/forums...post1597514644

E.Murray

Interesting. I wouldn't think just a leak somewhere in the system would cause it to both open and close (since both are vacuum-operated). Every single hose on the car is new, as are most of the vacuum-operated things. But I'll quadruple-check them and see if I can hunt it down. Thanks.

Dave J

My money would be on the wiper door relay. The difference in vacuum between your two scenarios would make a marginal relay do that. I've seen it on several other cars.

E.Murray

I replaced the relay Saturday and still had the issue on a short test drive - high vacuum opens it, low closes it. I still don't understand how a leak somewhere would cause this. It that really possible or is everybody just jumping to that conclusion? A new actuator isn't cheap and I hate to spend the money if that's not the problem, but I don't see any other possibilities. It's not like the system is all that complex, right?

Dave J

PM sent

theandies

Do yourself a favor and go buy a mity-vac if you don't already have one. You can test individual components which will save you time and money.
Have you changed the check valve at the vacuum source? Should be a silver component on the source line (typically on a fitting behind the carb between the distributor) that has one input fitting going towards the manifold and two coming out.
What happens when Idle or part throttle you're pulling more vacuum then when you stomp on it or do a quick off idle acceleration. If the check valve is bad you lose vacuum in those conditions and you door or headlights pop-up then go down as you let off (vacuum building back up). The check valve isolates the vacuum system from the manifold in these situations to keep vacuum in the system.

EDIT - Do a search - I've been on this forum since shortly after it started and I can say in the C3 section wiper door and headlight opening/closing/weird stuff is the single most talked about topic. There are tons and tons of posts on this subject and a lot of great information. The problem with these symptoms is there are different things that can cause what your seeing. Study the system and know how it functions will help a lot in figuring out whats wrong.

E.Murray

After a conversation with Dave, I'm going to test the components individually with my Mityvac. Only way to be sure. As far as the check valve, that's good to know. The one I'm using is of "unknown" condition. Safe to say that this one will be solved this weekend! Then it's only the really expensive and ugly things to worry about...