CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Humming van

i just recently got a 1983 dodge B-150 van with a V-6 Motor when its idling you can hear a loud hum coming from the engine compartment.but when you start driving it goes away.but soon as you come to a stop it starts humming again i took it to the shop the mechanic found a few vacuum leaks.and repaired them all but could not find where the hum comes from.even after he did the repairs it still hums and it is very very irritating to hear. i still think it has a leak somewhere because when ever i turn on my A/C it blows out threw the vents just fine but soon as you start to accelerate the air stops coming out of the vents but if you let off the gas pedal fully the air comes back on which is a killer in this Oklahoma heat

Have you lifted the hood and listened for the source?
There are tools, such as a “mechanics’ stethescope”, a length of metal rod, or even a funnel turned large end out, that can help locate the source. There are even sophisticated pieces of equipment that are basically unidirectional mikes or even piezoelectric linear accelerometers, that can help.

But it start by listening with the hood up.

If the mode changes in vent system when accelerating there’s a vacuum leak in the vent system. One component in the vent system vacuum circuit is the vacuum reservior. This holds a reserve of vacuum to the vent system so when accelerating the mode doesn’t change in the vent system.

This vacuum reservior is located under the hood and looks like a black plastic ball. If the reservoir is cracked, the mode in the vent system will change when accelerating and could be the source of the hum when idling when the engine vacuum is the highest.

Tester

My Family and friends have all looked at every vacuum hose and line we can see we have listened in just about every way you can to try and find the sound sitting and driving. we found the vacuum canister it looks like an old black coffee can it does not have any visible cracks or holes the humming is driving me crazy but there nothing i can do its my only transportation i am in a wheelchair and need my van so i really need to try and find this Mystery hum before i go nuts lol

thanks for everyone’s help and suggestions please keep them coming i will try them all until i get this fixed

heres a picture of the motor sorry its from a cell phone

p 00011

My choice for a tool to help me locate such a noise is a length of garden hose. Don’t try to use 50 foot. bit three to five foot should be good for most situations.

I think Tester nailed it and add that it is probably a leak in the blend door actuator diaphragm.