Vacuum hose?

53ryder

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Working on my '87 5th Avenue. Yesterday discovered manifold vacuum pressure at 15 pounds of mercury. A tad low. Been suggested to me to replace soft vacuum hoses. Ok. So which brand of hose with an inner diameter of 3mm or 3/16" should I try? The outside dimension is 8mm or 5/16". Thoughts?
 

Aspen500

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Pretty much any hose a parts store has will be fine. There is REALLY good hose available, that even has a cloth braiding . Only place I'm aware of to get it is an Audi/VW dealer and it's what you would call pricey. Probably overkill for what you need though!

With 15" at idle, it kind of sounds like the timing chain may be loose (i.e. "stretched") and the cam timing is retarded, provided it's stock engine with a stock cam.

To get pick nitty, chains don't really stretch, the connection between the links wear. It isn't much per link but, ass them altogether and I've seen chains grow to where they seem to have an extra link when compared with the new one. Timing chains are a big problem these days, especially on engines like the GM EcoTech and the GM 3.6L V-6, most with less than 100K miles. He says, going off topic again.:oops:
 

BudW

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I generally do not measure the (inside) diameter of hoses. I determine how much of each size, then take examples of each to part stores. If your hoses are stretched or broken at the ends, then cut back a few inches and take the cut-off in with you.
Hoses are sold by the foot, so if you need say 30 inches (total) of one size hose, just order 3 foot. Most part stores usually will give you about 13-14 inches per foot sold.

Just remember it is easier to make a hose shorter, than it is to make a hose longer after cutting it too short.
Now mumbling incoherently about measuring twice and cutting once . . .
 

53ryder

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I'm thinking (under my hat of course) that if changing out the hoses doesn't do much (I won't be surprised if nothing much happens but I'm still going to swap them out anyways) then most likely the next thing to do is the timing chain.

The engine is stock as best I know.
 

Camtron

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A can of carb cleaner or Wd-40 can be useful for finding vacuum leaks. If you spray it on or close enough to the leak, it will cause a slight increase in rpm helping locate it. Could have multiple hoses leaking or hose/s and carb baseplate gasket ect... Just help cover the bases to limit trips to the auto parts store.
 

69-

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Pretty much first thing I do on a new old car is checking hoses. Thats the easiest part, takes a little time, one by one. Then, most likely nothing changes.

Inclueing fuel and vac hoses. Those things are not to stay say 40+ years. Just have them fit snugly and you'll probably be fine for the next 20+ years :)

Add some new shocks and your ride maybe alright already.

Unfortunately, my lady gives no permission to buy car number 6... Love to have like 3 projects at the same time...
 

BudW

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Really, most any kind of spray cans will do the job.
I like using carburetor cleaner for many jobs, but not for this (for it might remove or discolor the paint).
Brake cleaner, WD40 and maybe 1,000 other spray cans will do the job. Avoid spraying close to the top of carburetor when engine is running for that will give you a false result. When the spray aerosol reaches a vacuum leak (carburetor base gasket, vacuum hose, intake gasket, or whatever), the engine speed will noticeably go up (or down) then level out once spray stops. A repeat performance will help pinpoint the problem area.

Unfortunately, my lady gives no permission to buy car number 6... Love to have like 3 projects at the same time...
I have six vehicles - but the issue I have is my lady is very good about giving me more projects to work on before I can work on my own projects . . .
 

Ele115

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A propane torch will do just fine too. You obviously don't have to light it
 

Aspen500

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Propane is the preferred method. One downside to it is,,,,,,,the cooling fan air flow tends to blow it away. Almost need the fan blade off or some kind of dam to deflect the air flow. Of course, with any spray liquid that's flammable, be careful of the ignition system,,,,,,,,,,,just in case. Then again, it would reveal poor plug wire insulation. :eek: A non-flammable spray will help find leaks but a flammable one will make them more pronounced. Unlike propane, the liquid temporarily plugs minor leaks even if not flammable and if flammable, will be burned in the engine.
 

Ele115

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Pop the belt/s off for just a minute if you want. They are super easy. If you epectrics, pop the relay
 

53ryder

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So basically I'm checking to see if anything is leaking out by spraying WD-40 or carb cleaner or something and watching to see if anything is bubbling then? I get the fan making it hard to see what is going on.
 

BudW

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It won't bubble, per se. If the aerosol spray finds a vacuum leak with engine running, it will get sucked into the leak. The aerosol is flammable so it will cause the engine RPM to either raise up (noticeably) or lower down. The RPM will resume once spray has left the area of the leak.

The fan has a tendency to blow the flammable aerosol elsewhere, sometimes. I don't notice this to be a big concern, but it can be. Either way, perform the test outside. A spark somewhere could lead to fireworks.
Aerosol Flame.jpg


Bubbles would be present in the absence of vacuum (wait, is that a double negative?), like an aired tire with a nail in it. with a bit of soapy water, you can find the leak via bubbles. There will not be any bubbles with a vacuum leak.
 

AJ/FormS

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Yesterday discovered manifold vacuum pressure at 15
Lots of things can affect the measured idle-vacuum on a given engine. They can be divided into three major groups; mechanical, tune, and other.
>As to mechanical; most notable are;
valve lash,
ring seal,
cam-timing, and
exhaust back-pressure.
> as to the tune;
idle-speed, idle-timing, idle-load
AFR, fuel level,
oil level, coolant temp
one or more faulty plugs or plugwires, or a cracked/tracked cap
> as to other are;
a stuck-open EGR valve, a faulty PCV or it's hose,
a ruptured brake booster diaphragm,
leaky hoses or gaskets, electrical load,
and a major player is always the possibility of a faulty gauge.
 
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