Weird knocking noise from top of engine?

[shahking1120]

Hey everyone,

I'm getting this annoying knock/tick noise from the engine bay, its been going for maybe 4-5 weeks now.

It almost for sure is happening at idle and startup, goes away sometimes but comes back 90 percent of the time.

I used to think it was a bad pulley, but after looking into it this morning, the sound is coming from the top, under the cover for the intake manifold.

Not sure if its present moving at higher speeds, my exhaust covers it up.

I've listed a youtube link below of my video.

No codes, no change in driving ability, very well maintained, Ive had the Tahoe since about 44k miles and now has 193k.


2011 Tahoe LT, afm disabled around 60k I believe.


Any help would be greatly appreciated.

 

[OR VietVet]

You need to get a mechanic's stethoscope and pin point that noise. It almost sounds like the a/c compressor clutch engaging and disengaging but like you said, it sounds higher up. Maybe even a tensioner or idler clacking. That stethoscope will pin it down.

 

[Foggy]

Sounds like you have a lifter and/or rocker arm failure on One Cylinder
Take off the valve covers and check !!! Especially before you wipe out the
camshaft and send metal all thru the engine

 

[shahking1120]

See, I was under the impression if its lifter/rocker arm issues, that it would be constant.

Its pretty intermittent, and along with the noise, I get small surges in idle, as if i was slightly revving the engine but constantly..

Please correct me if im wrong to assume so.

I unplugged the sensor under the engine cover on top and it went away for a while, but always comes back right when I plug the connector back in.

 

[OR VietVet]

See, I was under the impression if its lifter/rocker arm issues, that it would be constant.

Its pretty intermittent, and along with the noise, I get small surges in idle, as if i was slightly revving the engine but constantly..

Please correct me if im wrong to assume so.

I unplugged the sensor under the engine cover on top and it went away for a while, but always comes back right when I plug the connector back in.

Care to share which sensor you unplugged? When you say you unplugged the sensor and it went away for awhile, do you mean it went away and came back after awhile when it was unplugged or it went away till you plugged the sensor back in. Did you ever hear it when that sensor was unplugged?

 

[wjburken]

See, I was under the impression if its lifter/rocker arm issues, that it would be constant.

Its pretty intermittent, and along with the noise, I get small surges in idle, as if i was slightly revving the engine but constantly..

Please correct me if im wrong to assume so.

I unplugged the sensor under the engine cover on top and it went away for a while, but always comes back right when I plug the connector back in.

On an engine that is idling at 500 rpm, each lifter is engaged roughly 4 times a second. The sound in your video is happening at roughly once per second which is not in-line, in my mind, with a bad lifter or rocker, but it is a good idea to pop the valve covers and take a look.

Are you saying that if you unplug the MAP sensor, the sound goes away completely, but when you plug it back in, the sound comes back?

 

[shahking1120]

Care to share which sensor you unplugged? When you say you unplugged the sensor and it went away for awhile, do you mean it went away and came back after awhile when it was unplugged or it went away till you plugged the sensor back in. Did you ever hear it when that sensor was unplugged?

I believe it is the map sensor, the one hiding under the cosmetic panel on top of the engine.

If I unplugged it, it took awhile for the sound to come back, but as soon as i plugged it back in, the noise started immediately. So yes I did hear it when it was unplugged.

But im gonna go back out soon and confirm that last part.

 

[shahking1120]

On an engine that is idling at 500 rpm, each lifter is engaged roughly 4 times a second. The sound in your video is happening at roughly once per second which is not in-line, in my mind, with a bad lifter or rocker, but it is a good idea to pop the valve covers and take a look.

Are you saying that if you unplug the MAP sensor, the sound goes away completely, but when you plug it back in, the sound comes back?

Thats what I was thinking, ill get around to the valve covers later this week or weekend.

It goes away when i unplug it if it was making the noise at that moment, but it will come back. But no matter what, when I plug it back in, the noise starts right away.

 

[OR VietVet]

So, just unplugging that sensor changes something in the communication with other components and that could be why the noise stops but still comes back even when it is still unplugged. That, IMO, does not indicate that the particular sensor you unplug is the source of the noise. I am assuming you are getting codes when you unplug. What are those codes?

By the way, that does look like the MAP sensor but it also looks like the bracket that is on top tha holds in to place has a missing hold down screw.

 

[iamdub]

Run it with the serpentine belt off and see if anything changes.