Vacuum Lines

[snoopyloopysk8a]

What exactly do vacuum lines do?

[curtis73]

Many items about a car are vacuum operated. Things like power brakes use vacuum for power assist. Older cars (50s and 60s) often used vacuum to operate headlight covers, windshield washer pumps, windshield wipers, and even cowl induction hood scoops.

Since vacuum changes depending on how much right foot you have down, things like emissions equipment use vacuum to determine when to operate. The EGR valve recirculates exhaust to cool the combustion which has a benefit of reduced NOx emissions. The EGR valve only opens at part throttle, so it uses a vacuum signal to tell it when to open.

The charcoal canister collects fumes from the gas tank and uses a vacuum signal to know when to open up and suck those fumes into the engine.

Cars with computers use vacuum signal to determine how much load you are placing on the engine as one of the factors in determining how much fuel to inject.

Have you ever turned on your heat or A/C and heard a hissing in the dash? Many climate control systems use vacuum diaphragms to open and close doors in the heater to select inside/outside air, and to direct which duct gets the flow; vents, heater, or defrost.

[snoopyloopysk8a]

ahh, ok. thnx alot, man. can the car operate without them?

[public]

Yes. But leave the Brake Booster connected. No power brakes SUCKS big time. Besides, this does not use any power from the engine. On the older carburated motors you could cap off all of the vacuums except the distribuiter and run fine.

[curtis73]

For the most part, yes. Most engines from 1973-on are tuned with fuel and timing curves the reflect the use of emissions equipment; specifically EGR and Catalysts. Just disconnecting the EGR on a car can make it detonate very violently and shorten its life. You can tune most of that out by retarding the timing a touch at the cost of a few HP. If you have a newer car with EFI, you'll need at least the vacuum line or sensor for the computer to run things. Otherwise, if you can live without all those options, ditch them.

What year and make is the car? Unless there is a leak or a malfunction, the emissions equipment shouldn't account for more than a couple HP loss, even on early 70's cars. Like Public said, you can run only the necessary stuff as long as you cap them properly to prevent leaks, but depending on what year it is, some parts are vacuum operated while others aren't... like in the late 80's GM stopped using vacuum advance ignitions... stuff like that.

[snoopyloopysk8a]

1988 Honda Accord LX-i. I was wondering because I wanted to put a CAI on it.

[public]

Yeah, DIS rules. No more cap and rotor crap since, what 87?. And I also love the electronic EGR valves on GM cars. On the newer cars 1990 or so on up, leave things as designed.