Funny Noise

When I turn off the ignition, as the motor comes to a complete stop from idle, I can hear a strange very brief whoosh of something like compressed air. Kinda like a loud wheeze, it's hard to put into words.

The 1980 long-block motor received a stock rebuild about ten years ago and only has a 2,000 - 3,000 miles on it. It was in storage more than 3 years until recently when re-installed after the rotisserie restoration. The original 273 Commando AFB was re-built ten years ago as well (I just slapped it back on this time without having doing any new work on it). I just drove it on the highway for the first time in 3 years (a ten-mile jaunt). It seems to idle a little rougher than I remember it, but I don't notice anything else amiss (I did replace the spark plugs before the drive). The distributor is a automotive chain store single point style replacement.

First photo shows engine installed after the rebuild ten years ago. Second photo shows same engine installed after being repainted to correct Commando color scheme. Third photo vehicle as purchased, last photo currently awaiting headliner and windows.

I think I would do a compression test, and maybe a leak down test if necessary.

"Rig" yourself a temporary way to kill the engine with a long cord, scrap wiring, extension cord, use your mind. "Rig" a switch inline with the ballast circuit so you can start the car, then take your temp switch and kill it. Now just do that several times, while listening from several positions, both sides of engine, leaning down near under wheels, etc. Might try it near the back of the car as well.

Trouble light? Remove bulb, put a penny/ washer/ coin in the bottom to short the socket, screw bulb back in. You now have a switch. Take alligator clip leads and wire the two plug prongs in series with ballast resistor.---Kill switch!!

"Something" that has worked well for me over the years is some sort of scrap of hose. Anything. Hold it to one ear and probe the other end to listen. this method is excellent EG for finding exhaust and sometimes vacuum leaks

How about brake booster?

A neighbor/shade tree mechanic listened to the engine shut-down and said the quick wheeze noise was coming from the carb/air filter and nothing to be concerned about. I am still going to start off by doing a compression test (when I get around to it).

I'll bet you, that when you hear that sound, the crank is just finished moving, and one piston is bouncing back off the bottom of a compression stroke, pumping air up into the intake, past an almost-closed intake valve.
It may be that your butterflies are a tad far open, or that your idle-speed is a tad high.

That must be it, good job in diagnosing the mystery.

I'm just guessing, and there's no money on the bet ...... lol.

I’m with AJ. Turn the engine over by hand, when you do you can hear a woosh as the valves opening on the compression stroke.. either intake or ext and will hear the air “moving”…

67Dart273 said:

Trouble light? Remove bulb, put a penny/ washer/ coin in the bottom to short the socket, screw bulb back in. You now have a switch. Take alligator clip leads and wire the two plug prongs in series with ballast resistor.---Kill switch!!

Click to expand...

Probably should include a reminder to remove the coin after using the kill switch