Question: mystery vacuum leak, worse when I turn lights off

[tonyponykay]

when i turn the lights on, the minor vacuum leak that I am trying to narrow down, virtually dissapears, and my lights do come up and work fine.

then when i turn the lights off, ooo i gota rumble fumble vacuum leak that messes with the engine for a little while, till after a few minutes it settles down to the normal state which is: runs smooth with a small miss-like vacuum leak, as if on the old Quadrajet the bottom plugs were leaking gas into the intake, (there's a Holley on there now) I don't know if Holleys can leak like this, might need a float adjustment, haven't gotten deep into it yet.

But I am wondering what would cause the vacuum leak/rough idle when the lights are turnned off and (say after a tunnel). I was going to replace every vacuum filter and relay i could find but I thought I might ask and see if anybody has an idea that would save me the cash/work.

hnoes

thanks
tony;help

 

[73shark]

Maybe a leak on the "down" side of the headlite switch valve/hose??? Might check the hose diagram in the AIM.

 

[tonyponykay]

my aim (from ecklers) is new arrival last week, but pages are faded into bleary messes mostly hard to read, havent found many things in that AIM, one of them being that vacuum diagram. have a page number by chance?

 

[73shark]

First if your AIM is illegible, send it back and get a refund. There's plenty of good vendors out there that carry it. Corvette America even has it on CD.

In mine ('73), it's on pages 12C-7, 8, & 9.

 

[82ColEd]

You might want to try and run past this troubleshooting guide HERE

It made sense after a while (and after reading it 4 times. ).

Good luck with it, let us know how it goes..



-Stefan

 

[Mr. Chuck]

Your trouble shooting guide is well done, nice piece of work!!!

Regards:

 

[Mr. Chuck]

Assuming you have done a good visual inspection of the accessable vacuum lines at head lights and in the engine compartment and didn't find any loose or cracked lines. You may want to try the following method I have used: spray very small amount of starting fluid or carb cleaner on suspect vacuum connection, with engine running, changes in engine as a result of the intake of the spray, you can help zero in on the location of the leak. Use spray with one of those tubes to apply a small amount at the specific connection, around the head lamps vac lines and on the engine vac along the driver side fender well areas. Under the dash at the manual control or light switch require the old touch and feel method to locate.
Hope this helps.

 

[82ColEd]

Your trouble shooting guide is well done, nice piece of work!!!

Regards:

Assuming you meant my link, i cant take credit for that, thats from corvette-101.com, not me.. And yes, i thought it well done too.

Just found it helpfull when i was troubleshooting mine.



-Stefan

 

[Dunzvett81]

I have the exact same problem with my 81. When the lights go down the engine begins to idle rough for a few seconds then evens out again. I replaced the acctuators last year as the lights didn't work very well. Now the lights work pretty good with the left one always coming up a little slower. I replaced the filters and the lines are all in pretty good shape. The relays do have a leak and I think this is what maybe the problem is. (I hope) good luck with yours!

 

[tonyponykay]

getting on this soon, ripped out my air dam on parking curb

;helpwell, i was going to replace my rear spring this weekend, with monospring and work on this vacuum issue, but i parked at pep boys and the curb tore the heck out of my air dam under the front. :eyerolebash

So, I'm heading out to garage to get under there and see if any of it can be saved. The thing is, I think the curb ripped the holes open in the front section as well, so short of replacing the entire front nose of the car, I have to figure a way to repair those holes, the ones for the air dam and also the ones on each side that hold the rubber air foil to the edge of the lower part of the front. hnoes;help;help

anyway, I do think my vacuum leak is the relays, although I have tightened down the bowls on the holley carb and that, surprisingly made a nice difference. there's very small rumble bumble still, just a tiny vibration, but still, after turning lights off, yep, still got the big vacuum leak.. so I'm going to follow that trouble shooting guide and the tips you guys were kind enough to put here .. I'll hunt that booger down if its the last thing i do. (sound familiar?) :bash

thanks everybody

tony

 

[Whiteshadow89158]

Vacuum System

 

[73shark]

Might get some fender washer if the holes are ripped but still there. They are just a large washer w/ a small hole. Most hardware stores carry them.

 

[Dunzvett81]

Don't mean to hijack the thread. but no sense in opening a new one when my problem is basically the same. Here is the problem...
My lights operate pretty good, they pop up quick with the right one sometimes being a little slower and they both go down quick and together. However, when they go up or down (more so when going down)the engine vibirates and shakes a bit, can feel it in your seat they will eventually smooth out again. To me it sounds like there is a leak somewhere?
anyone have or had the same issue and any suggestions or remedies?? thanks

 

[LanceB]

tonyponykay that really sucks. Been there done that. My back end probably hangs out of the darn parking space I am so scared to pull up anymore!