Humming Noise Comming From Air Injection Pump?

[99 2dr]

Hello Again,
About every 5th time i start my truck there is a loud humming coming from the engine compartment. I cannot tell if the sound is coming form the Air injection valves on the exhaust manifolds or from the pump itself. I do know that when the pump turns off the humming stops. Has anyone else had this issue? The humming only lasts for about 20 sec and then goes away; when the pump turns off.
Thank you
Kyle

 

[SunlitComet]

it may be weak and need a few second when running to get rid of loose clearances internally causing a shift in the noise. Or the pump culd be frozen too.

 

[99 2dr]

I was thinking about un plugging the pump and running it for a few days just to make for sure that it is the air injection system. Is this going to cause any major problems other than just a check engine light?

 

[SunlitComet]

it might trigger a post a emmesions code or change performance but at least you might know if the pump is making the noise or not.

 

[99 2dr]

Sunlitcomet..... Can you please educate me on the operation of the air injection pump?..... Is it supposed to run all the time?.... Mine appears to run off and on...

 

[oldsalt]

It runs off and on 99. I can sometimes hear mine while at a light.

 

[SunlitComet]

From Alldata:

The electric motor Secondary Air Injection (AIR) system is used on the 5.7L to reduce Carbon Monoxide (CO) and Hydrocarbons (HC) .

The AIR system adds air (oxygen) to the exhaust manifold to continue oxidation after the exhaust gasses have left the combustion chamber. The heat from this reaction brings the catalytic converter up to operating temperature taster when the engine is cold. This system consists of an electric AIR pump, check valves, and necessary plumbing.


An electric motor AIR pump supplies filtered air from the air intake system to the AIR injection pipes.

The check valves, on the AIR injection pipes, prevent backflow of exhaust gasses in the AIR pump.

When the engine is started with a coolant temperature above approximately 15°C (45°F) or if the fuel system is in the Decel Mode, the VCM energizes the AIR relay. The AIR relay then energizes the AIR clutch, which directs air into the exhaust manifold ports.

The control module may turn the AIR pump OFF when any of the following conditions occur:

* The system is in the Closed Loop mode
* Any DTCs are set
* The system is in Power Enrichment mode for more than a short period of time
* Low manifold pressure (over run)
* Quick vacuum rise (rapid decel)

 

[99 2dr]

Thank you,
I am thinking that i just need to change the pump. Perhaps at 242,000 its just worn out. The only other thing i could think of was that the noise is being created by the air passing through the check valve, similar to blowing over a corona bottle.