jsol72

Hey Guys,

I have done quite a few searches here, but nothing i am reading sounds quite the same. On cold starup i am getting what sounds like a "whirring or whistling" (think of a bomb dropping in a cartoon...sorry, thats what comes to mind) sound coming from the engine bay. The longest the sound has lasted is about 3 seconds. 1993 LT1 stock, 64000 miles. Thanks.

jaa1992

Its the AIR pump cycling. The pump was located in the driver side light well before I removed it on my 92

jsol72

Thank you. So i assume this is just normal operation?

pcolt94

Although it could be a air pump, it runs a lot longer than 3 seconds. It runs for approximately 2 minutes depending on several inputs the ECM. Engine temperature and time from start are some of the factors.

A bomb might sound more like the ABS pump cycling which is about 3 seconds at 4 MPH. But the sound is not from the engine, it comes from behind the driver seat in the ABS compartment.

Do you hear the sound when you first start driving, or when your outside the car with the hood up?

Other possible related things could be vacuum leaks, bad belt, alternator pulley or bearing, bad bearing in another accessory item.

jsol72

i can hear it with the hood down, by the time i get out of the car to try to investigate the sound is gone. It is only there for a very short amount of time. I may try to to take a video, or even an audio sample and post it.

jsol72

Should have added it does not do it while driving, only after start-up for a couple seconds.

R59

I have a 94 lt1 does the same thing as yours. Only when it's cold does it do it. Mine has been doing it for a long time, after it warms up it goes away. I think it's the belt tensioner but not sure.

tehcarguy

My 86 used to do this on a cold start. I figured out the PO used some very thick fuid in the power steering. Replaced it with the right fluid and sound went away.

jaa1992

Yep, want to check? when the car is cold, open the hood and have someone start up the engine. Listen to the AIR pump whine. The louder noise you hear may just be a bearing going in the pump and thats why it only lasts for a few seconds.

Or it could be whine from the power steering pump or AC compressor or belt pulleys. You have to have the hood open to see and hear.

captbob33

I have this same noise on my 96 LT1. Noise is coming from the left front, I'm thinking it's a bearing going bad in the AIR pump, Alternator, Power Stearing Pump, Belt Idler Pully, or the Belt Tensioner but can't isolate which one.
What's the best way to determine which item is making the noise?

0Paul Ruggeri

Try taking the belt off and starting the car. If the noise isn't there, then you know its something the belt turns.

captbob33

I've done that and yes the noise did go away. The problem I'm having now is trying to determine which component is squealing.

leesvet

Its the belt tensioner.
As they wear, the hard nylon/plastic bushing allows the swivel arm to start creeping out of the housing. Its damn hard to see, but it chirps like mad and will drive you nutz.

If you see the tensioner moving ANY...as the engine idles, as in bouncing around a bit, thats your squeek, chirp or whatever you wanna call it. The engine should idle with the belt moving around the tensioner like it was solid...no movement what so ever.

Next would be to spin each accessory by hand and feel for one thats the least bit rough or not silky smooth. Alt, water pump, even the PS pump.

GrnVette94

I found my bad idler pulley by using a long screw driver or pry bar like a tuning fork. Put the metal end on the bolt of the idler pulley while the car is running. The vibration/sound will travel up the bar. you can feel it and hear it if you put your ear next to the bar. As you move the bar from accessory to accessory you will know which one is bad.

leesvet

A safer way of doing the same thing is with a section of heater hose or3/8 hose of some sort...that hurts lots less if it gets caught by a belt or pulley and you can move around with the end held in your ear.

pcolt94

That’s what I was thinking also right out of the gate. The screwdriver works OK for finding a sticky fuel injector, nothing moving. They do make automotive stethoscope for finding noises. It's a lot safer near moving pulleys and belts. I use to use the head sets from airliners that operated like stethoscope before they had the electric headsets.

If you don’t remember those headsets, you have not been flying long enough.