chasing another noise...

I've got a kind of "screechy" noise that I can't seem to locate. First, I thought it was supercharger belt noise since I had a lot of black dust. I have an idler pulley pulley setup and a KB with an 8lb lower and 3" upper... The idler was covered with black dust from the gatorback. I put a gates on to replace it and the noise was still with me...

I then replaced the serpentine belt with a gatorback and the noise is still there.

I removed the idler pulley setup and went back to stock pullies. The noise is still there.

The idler pullies don't make a difference when I swap them around.

The noise kind of sounds like a slightly slipping belt and is rhythmic. It is kind of screechy but no all that loud. The best way for me to hear it is get up to speed and let it shift into OD. Once there, moderate throttle pressures will make it sound. It seems as if I get a little more noise right when I tip in and right when I let off. It is not constant. It starts when the truck shifts into OD and rpms drop, but the load demand is still there.

It definitely is NOT detonation. I am running a full tank of 104 octane on my street program so that isn't it.

I can continue rotating out idler pullies and try the ones on the serp belt also and see if it is one of them...

I have rochester 50# injectors. Do they screech a little? Could it be the alternator? The P/S pump? "Cobra" water pump?

I have checked the color of the oil in my KB and it is still clear. I would assume that if a bearing was going on internally in the KB, it would blacken the oil, but I don't know...

Please give me some ideas here...

thx

ken

 

Ken,

Did you take the Supercharger belt off and drive it?

If not I would do that.

It is safe to do and will at least eliminate or pinpoint the KB.

Just a suggestion.

VINNIE

 

Ditto. I had a similar noise. It was almost like a stuttering noise. When I ran w/out the belt, I realized that the Gatorbelt that I had purchased a couple weeks before was now too long. I replaced it with a belt 1/2" shorter; and the problem was gone.

-Edward

 

Maybe a vacuum leak. I had a similar sound that only happened when the throttle body was part way open regardless of what speed and engine RPM.

Does the sound change pitch when the rpms change or vehicle speed changes? That will give you a clue as to if it is related to which rotating parts or not.

 

it doesn't seem to change pitch... just intensity. When I roll into it while in OD, boost climbs to about 10 or so and I can hear it. Right when I let off the rhythmic squeal/chatter seems to amplify just a bit but is then gone immediately.

It seems to almost HAVE to be something that is making noise because of load since it doesn't do it while just cruising. I have to get into it to hear it.

I'll try to find someone who can make a good quality sound recording of it and post it.

I'll remove the belt tonight and see if the sound is gone... that will narrow it down at least.

I have changed belts and I am tight enough for sure. I've tried with/without auxiliary idler setup with gatorback and ribbed gates and the sound remains the same, so it can't be belt related. The serpentine is a brand new gatorback which also did not change the sound whatsoever. I would think at this point, belts can be elimnated completely.