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Howling noise from intake

1K views 14 replies 4 participants last post by  LRDMOD 
#1 · (Edited)
Hey guys,

So I have an annoying problem. I recently rebuilt the top end of my 3.9, all went pretty smooth. A few tanks later I realized that my stepper motor was not working. So I replaced the motor and adjusted the base idle as per the RAVE manual.

To have the idle at a correct RPMs it has created a not so beautiful howling coming from the intake.

This sound only happens when the ICV hose is connected and below 1900 RPMS with engine at operating temp.

I can change the pitch when I squeeze the ICV hose as well. The old hose was pretty hard rubber that I thought was dry but is it supposed to be a harder rubber than lets say a coolant hose?

Thoughts? My radio can only go so loud!

Thanks!
 
#6 ·
The base idle adjustment should not be set to prevent stalling. It should be set as per the book. If If it is dying when you accelerate, something else is wrong and bumping up the base idle is just a band-aid.

That noise, sound more to me to be what I've heard from the ICV valve although louder than normal.
 
#8 ·
It sounds to me as though something else is wrong. You shouldn't have had to adjust that air bypass way out like that to get a strong idle. Any idea what your fuel pressure is ? Where is your timing set ?

My 94 lwb as an example idles strong @ sub 500 rpm and doesn't drop much if @ all when pulled into drive.
Do you have access to test book or rovergauge ? The icv can only handle so much and when you adjust that screw way out it maxes out the ICV valve's range/ability to compensate.
 
#10 ·
I dont know what my fuel pressure is, timing is 6 degrees RTDC.

I can have the idle at 500 strong, with no sound. Its just seems that the ICV cant compensate sometimes and the truck hesitates here and there. I thought the idle was just a little too low.

Unfortunately I do not, however it does seem that the ICV valve just can not compensate that hair.

I will bring the idle back down to 500 revs and see what the fuel pressure is at.
 
#15 ·
I solved the high pitch noise, thanks everyone for your help!

Turns out the hose I was using for the ICV valve was just different enough from a genuine hose. I attached a picture. Genuine is the top one, much harder rubber.

I think what was happening is that when the ICV valve was open the hose was collapsing, thus stalling the engine. When the idle was turned up less air was traveling through the hose so it wasnt stalling however it created the whistle.

I replaced the hose and readjusted the base idle to 525 rpms. Now I can hear again!
 

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