Engine: Hissing sound

[plee4139]

The car started to run roughly and when I opened the hood I could hear a hissing sound. I checked all connections but couldn't find any visible problem. Then I went on to our forum and it seems to be an intake manifold leak. I don't know if there's a hole in the manifold or if it's a bad gasket, as it would have to be put on a hoist in order to see it. Is it okay to keep driving it until i can get it looked at?

[Bud]

Which engine do you have as the V8 engines don't very often have an intake manifold leak. The sixes can have gasket failures but it's usually on the exhaust ports of the gasket. If you suspect an intake leak, don't keep driving the car as an intake leak can cause the cylinder or cylinders that have the leak to run lean which isn't good. Bud

[Noxnabaker]

My dad had a crack in the inlet manifold on the -55 Commander & when axelerating the engine almost died, went into a gas station & saw the crack. Got it welded & it was alright.

[harry]

Try spraying oil or WD40 around the intake. The motor should run smoother for a minute or two.
That would indicate a leak.

[Skip Lackie]

Another way to check is with a propane torch. Turn it on slightly, don't light it. Move the nozzle slowly around the intake manifold and the base of the carb with the engine running and the air cleaner in place. If the engine speeds up, that's where the leak is -- the leak is sucking in the propane and burning it.

[GrumpyOne]

Spraying carburetor cleaner is also useful for detecting leaks...

[LarkTruck]

The car started to run roughly and when I opened the hood I could hear a hissing sound. I checked all connections but couldn't find any visible problem. Then I went on to our forum and it seems to be an intake manifold leak. I don't know if there's a hole in the manifold or if it's a bad gasket, as it would have to be put on a hoist in order to see it. Is it okay to keep driving it until i can get it looked at?

Isn't your engine a 289? Why on earth do you need to put it on a hoist to check an intake manifold leak? Was your engine installed upside down? Sorry, I couldn't resist that one. I agree with the carb cleaner or 2+2 method of checking.
JS

[Lou Van Anne]

Had the same problem with my 259 Champ.....turns out a hose on the carb had come lose.....reattached it.....no more problem.....

[52-fan]

A hissing loud enough to hear easily does sound like a hose has come off or is cracked. The diaphragm in the distributor vacuum advance could also have ruptured. Try blocking/capping any vacuum ports to the carburetor or intake and see if the engine runs okay. Then connect them one by one and see when the problem resurfaces.

[studegary]

Does your Hawk have power brakes? The hissing noise may be coming from the vacuum line or the booster.

As said, this is most likely a vacuum leak somewhere. If it is enough for you to hear it, do not run the car much at all until repaired due to the lean condition in one or more cylinders.

I can't think of anything that would cause this on your car that would require the car to be elevated in order to diagnose the problem.

Also, it may not be a connection, but could be a split in a vacuum hose.

[plee4139]

Fears of welding or having to replace an intake manifold or installing a brand-new gasket were not , praise the Lord of Your Choice, The unwanted hissing sound came from the opening in a small L-shaped tube on the top of the 289 block which was missing a cap, thus causing the sound. It looked like there should be some kind of rubber or metal tube connected to it, but evidently not. Anyway, my shop handed me a bill of $54 and change, and then I handed back a coupon for $50m from them, and the rest was a wash. Thanks for your informed input.

[StudeRich]

I am pretty sure it was not in the "BLOCK", ...no Vacuum there.
Most likely a brass fitting for a Power Brake System that had been removed and the hole in the INTAKE Manifold, left rear improperly plugged.

[Dwain G.]

Small 'L'-shaped tube? Sounds like the PCV port at the rear of the valley cover on a '63 V8.

[plee4139]

I am pretty sure it was not in the "BLOCK", ...no Vacuum there.
Most likely a brass fitting for a Power Brake System that had been removed and the hole in the INTAKE Manifold, left rear improperly plugged.

Yes, the power brake system had been removed before I got the car. the plug must have just fallen off. The bill came to $54, but I had been saving a $54 coupon the shop sent me due to expire at he end of the month, and the rest was a wash. I guess that eventually every squirrel gets his nut.

[showbizkid]

Moved to Tech Talk - please make sure you post in the correct board Thanks.