71 454 vacumn leak rough idle

[Mike S.]

71 454 rough idle .#8and 5 cyl low rpm drop on cyl balance test.i can block off vacumn line going to vacumn tank smooths out .did smoke test on vacumn tank no leak. disconnected vacumn hose for headlamps and wiper at vacumn tank and smoke test all leaked out bottom of vacumn relay switch .with nothing on .i think relays are ok every thing works fine. do vacumn check valve between vacumn source and vacumn tank have any thing to do with it.

[Patrick H.]

Re: 71 454 vacumn leak rough idle

It's easy enough to check the valve to see if it works or not. And yes, it can affect the idle. It's also easy enough to bypass and see if that helps.

I'd also use a vacuum pump on the vacuum tank with all the extra openings blocked off. I wouldn't necessarily trust the smoke test. I'd also check the headlight canisters with a vacuum pump on front and back.

Patrick

[Mike S.]

Re: 71 454 vacumn leak rough idle

thanks

[Mike S.]

Re: 71 454 vacumn leak rough idle

could a vacuum over-ride valve for under dash or vacuum reserve valve.be the problem.

[Jack H.]

Override switches beneath the strg column...

were intended to FORCE the wiper door or the headlight buckets into their open position by venting vac to the respective control relay. That's the way these vac circuit normally worked when you pulled the HL switch to raise the headlights or hit the wiper switch to open the wiper door. Both the normal control switch as well as the manual override switches vented vacuum to their respective control relay.

So, what's the point? The point is the engine didn't stumble/fall at idle just because the headlights were turned on or the wipers were in operation when the car was new! Heck, you expected the car to be able to stop at a traffic signal with even both the headlights and WSW working.

Several catalog houses (Mid America, Corvette Central, Dr. Rebuild) have nice little phamphlets to explain the Shark vacuum system and give you troubleshooting techniques.

[Mike S.]

Re: thanks jack *NM*