SOLVED!!! Loud Screech from the 454!!!

[KendallP]

***EDIT***

Note 1: I believe all videos posted below are a must-view before comment...

Note 2: Belts reinstalled now since they nor the components they run are the culprit.



I picked up the Winnebago from the storage yard yesterday afternoon. Of course I warmed 'er up a bit and then off I went. About a mile or so down the road, I began to hear a bit of a whine. Within another mile or so it became a loud screech... almost a vibrating metal on metal sound.

My first instinct was vacuum because in my mind, the most interesting part of this phenomenon is that it completely disappears for an instant when I stomp on the gas. In that moment, RPMs are changed only slightly. This occurs without fail every time and often more pronounced than my video. See link below...

I removed all belts. Screech still there. Finished up around 10 last night.

Mexicowanderer recommended next I Vice Grip pinch the small hose coming out of the "protrusion" off of the smog pump. So this morning I got up and did that. Then starter 'er up. No noise. Great!

Then I removed the Vice Grips. Still no noise. Dang.

I wish I had starter 'er up first.

So now I'm left to wonder whether the pinch did something or if this only occurs when she's warmed up.

I plan to put 'er back together and warm 'er up with the water pump running again to see if the noise comes back. If so, then I will retry the pinch.

Any thoughts?

Note the noise disappearing for the instant I stomp on the gas...

https://www.youtube.com/watch?v=Rq5XvVMwMVc


New videos...

https://www.youtube.com/watch?v=ImTWQeb8jNE


Upon shutting 'er down after the video above, I noticed another sign. So I starter 'er up again for the following video. Silence until I gave her just a little gas. Then a few more pedal stomps and shudder' down (that's Jefferson State speak for, "Turned the ignition switch to the 'off' position."...

https://www.youtube.com/watch?v=klk4B7nHsjI
.

[KendallP]

Ductape wrote:
I had cam bearings fail on an engine once... sounded the same as a screeching accessory bearing or loose belt. Hope Mex is right.

Lord, me too.

My neighbor threw that possibility at me last evening. The ramifications were not lost on me.

But after that, my other neighbor, a pretty mechanical savvy lady listened to it and agreed that a cam bearing screech should not go silent the instant you stomp on the pedal, i.e. when vacuum is near zero.

Mex? Your thoughts?

[KendallP]

smkettner wrote:
Does the noise change more with engine RPM or with vehicle speed?
While parked or just in motion?
Does the engine shift much when you flog it? motor mounts?

Sorry can't see the video yet.

Yes. Change in pitch with RPMs

Either

No

[Ductape]

I had cam bearings fail on an engine once... sounded the same as a screeching accessory bearing or loose belt. Hope Mex is right.

[time2roll]

Does the noise change more with engine RPM or with vehicle speed?
While parked or just in motion?
Does the engine shift much when you flog it? motor mounts?

Sorry can't see the video yet.

[KendallP]

MEXICOWANDERER wrote:

I was forced to diagnose this krap when customers gave orders for a new alternator, and I knew the WHISTLE to be emanating from the Air Injection Reaction Pump. GM's had this setup for years - the AIR pump nestles just below the alternator. I always had Armando pull all the belts just as you did and found many a flaky water pump bushing, weeping power steering pump or hose and noisy AC clutch bearing.

Well... as I mentioned... my very first thought was vacuum. And I have always felt it was coming from somewhere near the front passenger's side of the engine, yes.

Given that the alternator was recently rebuilt, it was not unreasonable to also begin there.

And no. It was not really intermittent. I started 'er up yesterday afternoon, warmed her up a bit and drove. A mile later I began to hear a slight noise and within another mile... it was no longer slight. The rest of the day as I worked on 'er... the noise was always there with the engine running. Until silence this morning... the ONLY intermittent part was when I stomped on the gas each time.

And if performing the necessary acrobatics working in this doghouse to get belts off were a little easier... I might be a little happier about eliminating all of those possibilities when a vice grip pinch might have done it 5 man hours ago!

Still love ya', though, gramps. Always.

Funny thing is... my wife's 4Runner makes a very slight whistle that corresponds to RPMs. I felt it was likely some O2 sensor issue or something. Been years without further issue, so it remained low on my massive list. But I felt today's issue was somewhat akin to that... only MUCH louder

I will carry out your orders and report. Just wanted to get this posted to see if anyone else has ever encountered this issue. Sure wish I had taken you up on that recommendation to purchase a pair of chain-mail gloves right about now. I know, I know. Dang kids never listen and have to learn everything the hard way. Blah blah blah.

So the question remains...

If the A.I.R. pump is the issue, will it be ok to put 6 hours or so on her with a temporary fix?

[KendallP]

the bear II wrote:
Hard to turn Alternator
Bad Fan Clutch - hard to turn
Same for water pump
The above will cause a screech at low RPMs which may go away when you hit the throttle.

Oil Pan dented

Thanks, but key point missed: All belts off and noise still there.

Perhaps I'll update the OP to mention this earlier on.

[MEXICOWANDERER]

It's coming to haunt you...





It was intermittent to begin with. Why do you wonder that it does not appear and disappear on command of a pair of Vice Grips (or not)?

Reassemble and DRIVE THE RIG with this small hose PULLED OFF and a sheet metal screw blocking off the uncoupled hose.

I was forced to diagnose this krap when customers gave orders for a new alternator, and I knew the WHISTLE to be emanating from the Air Injection Reaction Pump. GM's had this setup for years - the AIR pump nestles just below the alternator. I always had Armando pull all the belts just as you did and found many a flaky water pump bushing, weeping power steering pump or hose and noisy AC clutch bearing.

[the_bear_II]

Hard to turn Alternator
Bad Fan Clutch - hard to turn
Same for water pump
The above will cause a screech at low RPMs which may go away when you hit the throttle.

Oil Pan dented