Poor Vacuum on Older Chevy Pickup?

Question

On my 1992 K1500 Chevy Pickup my vacuum pressure seems to be a little low, I cant seem to find the leak, does anyone know where I can find a vacuum helper for it to help boost the pressure, I have my cruise control connected to the line and it just kicks on and off because of the pressure. BTW its a 5.7L 350 engine. Thanks for your help...

Answer 1

For starters you are looking for vacuum, not pressure.  They are the exact opposite of each other.  Next, the easiest way to find a vacuum leak is to disconnect one end of the vacuum lines, and introducing pressure to the system by using compressed air.  Be careful not to exceed 16 psi.  When you have pressurized the lines, spray them all with soapy water, and look for bubbles.  When you find a leak, keep inspecting all the lines, and the vacuum chamber.  If it is like MY K1500, it is right next to the fan shroud on the left (driver's) side of the truck.  Just because you found a leak doesn't mean you found them all.  Good luck.

Answer 2

Vacuum is pressure. It's just lower pressure than on the outside. Put a vacuum gauge on the intake and start taking off lines and plugging the ports to find the leak. You can also get a little hand vacuum pump with a built in gauge for $15 and put vacuum to each line to see if it holds. There are no vacuum assists, and you need to find the leak anyhow. Your engine could be running very lean if it's a bad leak.

Answer 3

Im having a thought as to the possability you hooked to a special ported line and were supose to hook to a non ported vacuum line. the live going to the brake booster is non ported, it needs a lot of vacuum presure to work well, the much smaller lines are often only slight vacuum for more sinsative sensors and such.  

Answer 4

  

   First of all, vacuum is the absence of pressure. So really there is no way to "boost" it artificially, only enhance it.  The usual means of doing this are, as you have attempted, to repair any way that outside,  or pressurized, air can dilute the vacuum.

   First though, why do you suspect low vacuum?  The cruise control can be malfunctioning for a variety of reasons and low or irregular vacuum will let itself be known in other, more noticeable ways; particularly in engine performance and, eventually, in probably an emissions code (such as a lean mixture on an O2 sensor). If you are intent on correcting this problem on your own and have a good reason to suspect a vacuum problem it would be well worth the relatively small investment on a vacuum gauge.  If you do in fact have a vacuum leak you are far better off repairing it than trying to hide the symptoms.

   Another worthwhile investment would be a manual from Haynes or the like which will not only help in diagnosing vacuum leaks but should also give some help with your cruise control problems.

   Good luck!

Answer 5

Vacuum is measured in inches of mercury. For this purpose an inexpensive vacuum tester will do just fine. Plug it in anywhere between the throttle body and intake valves. Search around a little and you'll find a nipple on the intake manifold. You can always make-up some reducing bushings and plug in at the power brake booster vacuum line. You should be getting a minimum of 12 inches of Mercury at idle.

Answer 6

I can give you some things to look for but if the engine is old and is wore out it won't build much vacuum, however if it has power brakes and a vacuum booster on the brakes my guess would be that you have a check valve bad on the booster, This is one issue to check. To do so start the rig let it run for a few seconds on the brake booster remove the clam with a pair of pliers by squeezing the tabs together slide it back past the plastic and pull the hose off with a twist, if you here a suction when you remove the hose then it's ok if no noise when you pull the line then it more than likely has a bad check valve and you can buy them at the auto parts store. Next with two people one starting it and one with his finger over the hole of the aforementioned hose start the engine (Be careful) If you feel suction while the engine is running then it is not likely you have engine problems you may have an intake leak or a broken tee somewhere on the engine, to test get a plastic spray bottle add some dish soap and water and while the engine is running spray it around the engine on vacuum hoses ONLY if the engine picks up speed then you are close to the leak keep going till you find it. This is assuming your engine runs good, and you can buy a hand vacuum pump at the auto stores to test hoses with that you may suspect of leakage.

Answer 7

start your truck and spray some starting fluid around all fittings and the intake gasket.

Answer 8

A quick and simple old school method of finding a vacuum leak it using 2+2 carb spray with the extended nozzle. Spray a short blast around areas that could be losing vacuum while the motor is at idle. When you hear the motor increase in rpm's, you have found the leak.

Also you can go to the junkyard a get a vacuum reserve tank off of a older vehicle. They are black plastic and are the size of a softball.