Help with squeal/whine from engine AMC360

[90supra]

I am trying to determine the cause of an engine squeal/whine (depends what you want to call it). It first happened back in January/February but was not consistent enough or lasting long enough to allow me to trouble shoot. Fast forward to about a month and a half ago and it came back. I wrongfully assumed it was a accessory pulley causing the issue. Removed all belts and the noise is still there. Here are some videos:





It is the predomiant noise in the videos which is surprising as my jeep isn't very quite. The noise does seem to be throttle or load dependent and fades out above about 1/3 or half throttle. Things that have changed over the time from first noise to now:
oil pump mid-plate installed (original gears used)
spark plugs and wires.
oil changes
some vacuum lines replaced/removed (np208 swap)

I don't believe it is the stock motor from the Jeep. Previous owner said it was out of a 75 or 76 Cherokee. There is a Howell TBI, Edelbrock Performer intake, HEI, and Doug Thorley headers feeding into a 3" exhaust.

Hopefully someone can give me some direction to head in. Is the motor about to nuke itself? Should I hurry up and build the 401 to replace it? Is it something stupid and small? Any help is appreciated.

[68glad]

sounds like a vacuum leak.

[Tatsadasayago]

Definitely a vacuum leak.
You can localize the leak using two methods:
Get a length of hose, say 3/8", hold one end to your ear while moving the other end around the engine.
The other method is to use a spray liquid of some non-flammable type and squirt it around the intake and carb gaskets. When you plug the leak with the liquid, the squeal will stop momentarily.

I wager the leak is on the passenger side front of the carb. Why?
In the second video the sound changed as you moved left with the camera--and became more distinct when the upper hose and distributor were no longer blocking the sound.
The other giveaway is the sound going away when you open the throttle plates. Manifold vacuum drops and the squeal stops until vacuum comes back up.
Your carb appears to be a Holley 41xx series so check your vacuum ports for leaks and base plate for cracks.

Once, LONG ago, I encountered a similar sound at idle only and it turned out the be a smoked distributor bushing...but in this case I doubt it.

[90supra]

Definitely a vacuum leak.
You can localize the leak using two methods:

--SNIP--

Once, LONG ago, I encountered a similar sound at idle only and it turned out the be a smoked distributor bushing...but in this case I doubt it.

Thanks for the post. I hadn't noticed the change in sound lever until I was videoing for that. I will begin the search tonight, starting with manifold vacuum lines. Really wanted to get rid of the red tube any.

Also it is a Howell TBI setup on there, not that that effects the vacuum search much.

[Curly]

I'm not familiar with Howell TBI, but a quick google image search shows that it is a GM clone. Check your base gasket, GM had some trouble with the gasket blowing out (sucking in?) on some of their tbi set ups. I had one on an astro van that I chased for a while till some one told me to check the base gasket. Bingo! No more problems.
If you have access to scan data on the jeep, check your IAC counts. Mine were at 0, but I was too new to FI to realize that the PCM was trying to compensate for the extra air. Once I replaced the gasket, IAC counts went back to normal.

Curly

[Renodemona]

That's a completely normal sound for the TBI system working under IAC or Idle Air Control (normal low idle). The IAC might be a little long in the tooth so its sucking a bit of air. Replacement should be like $20-25, any GMC/Chevy TBI 350 IAC. Usually should go away when the throttle is advanced outside the idle range and the IAC is disabled as the butterflys open. If it is still whistling that bad at above say 1200 rpm, replace the IAC that should cure it. I'd also check the gasket around where it fits into the throttle body. Might be leaking a little bit of air from the housing if the gasket is dry and cracked away. Some of the noise is the injectors, try a fuel system cleaner or a rebuild kit for them depending on how many miles they have. Other than that, it sounds fine, just like any TBI system is supposed to. Just a little noisy, might be a combination of what I've described as well. Nothing to be overly worried about.

[FSJ Guy]

X2 what Renodemona said. The whistling is a little louder than what I'm used to, but it sure sounds like the IAC.

If you take off the air cleaner, you can put your finger over the IAC inlet on the top of the TBI unit and feel the air suction. I'd also try replacing the IAC, too. It is a "dumb" actuator, as in, there is no way for the computer to know if it really HAS moved or not. The computer just tells it to move and hopes (assumes!) that it does.

[Renodemona]

Older video, but TBI making same sound. Replaced my IAC after this, now less noisy.

https://www.youtube.com/watch?v=tilSHLfo0O8

[90supra]

Thanks for all the replys! I'm leaning towards IAC due to a lack of change when all the vacuums lines sprayed with soapy water as mentioned by Tatsadasayago and that the noise changed with the air cleaner removed. Maybe not changed but pitch different.

Unfortunately, a small oil leak turned into a miniature Niagra falls coming from underneath the Jeep. Looks to be timing cover to motor seam above the oil pump housing. AC and altenator were removed to find this. Plan is to remove everything, clean and reinstall with fresh gaskets. Will investigate timing chain condition once i'm in there.

Does anyone know a source for the oil pump pressure bypass spring? I have new pump gears and will probably install the bulltear relocation stuff this time but can't find the spring in those parts that I have.

[Tatsadasayago]

Another TBI sound like that I experienced was an injector that had small bits of dirt/rust/grit packed up at the injector pintle. I figured it out when I shined a timing light into the bores and could see a wedge shaped area in the fuel spray 'Umbrella' under the injector where gas wasn't flowing. When I cleaned the injectors the pattern was back to normal and the whistle was gone.

It's probably your IAC and it may only need to be pulled and cleaned since gunk does get built up at the tip.