High pitch whistle when cold on deceleration?

[bobthetj03]

Been going on for a while now, but when it's cold in the mornings, I get a high pitch whistle that I can modulate with the gas pedal, Seem louder on deceleration. After about 10 minutes in to my commute it goes away. I checked the vacuum lines going to the manifold and valve cover and they seem fine. I can't pinpoint where the whistle is coming from. Could it be a bad intake manifold gasket?

 

[Steel City 06]

Could be a vacuum leak in the brake booster. Do your RPMs go up slightly when you hit the brakes?

 

[03coloradowrangler]

my alternator whines or whistles when cold, once warmed up goes away. denso reman is in the mail.

i was able to pinpoint the noise with a tube, one side placed at my ear and the other near my alternator.

 

[Jerry Bransford]

Been going on for a while now, but when it's cold in the mornings, I get a high pitch whistle that I can modulate with the gas pedal, Seem louder on deceleration. After about 10 minutes in to my commute it goes away. I checked the vacuum lines going to the manifold and valve cover and they seem fine. I can't pinpoint where the whistle is coming from. Could it be a bad intake manifold gasket?

Vacuum leak for sure, vacuum increases when decelerating which would make any vacuum leak more noticeable. Start the engine then spray carb or TB cleaner at the various points where the vacuum could be leaking from. Vacuum line leading to the intake manifold/HVAC port on the firewall/vacuum reservoir under the battery, where the intake manifold seats against the head, or where the power brake booster's vacuum hose connects at both ends.

 

[bobthetj03]

I'll check those areas out, thanks. It's tough to isolate cause once I get to work the noise is gone, so I may need to let the jeep sit overnight and spray it when it's cold.

 

[CodaMan]

My did the exact same thing. It was a vacuum leak at the intake manifold. I tightened all the bolts and that stopped it for a couple months. It started back up so I replace the gasket. It's been quiet since.

 

[bobthetj03]

My did the exact same thing. It was a vacuum leak at the intake manifold. I tightened all the bolts and that stopped it for a couple months. It started back up so I replace the gasket. It's been quiet since.

I tried that. The last manifold bolt next to the fire wall seemed to be loose, so I tightened it and it went away for a short while, then came back, so I'm guessing I get to have fun removing the manifolds. I'll still try the spraying first just to make sure. Not looking forward to pulling the manifolds.

 

[CodaMan]

I tried that. The last manifold bolt next to the fire wall seemed to be loose, so I tightened it and it went away for a short while, then came back, so I'm guessing I get to have fun removing the manifolds. I'll still try the spraying first just to make sure. Not looking forward to pulling the manifolds.

I never had success spraying anything. The leak may have been in a bad location. One piece of advice though, if you're going to remove the manifolds remove or lower the fender. That 30 minutes it takes to remove that fender will save a lot of time and frustration.

 

[Nimbley]

It’s a vacuum leak. Vacuum is always highest on deceleration. Check the throttle body. They usually cause a whistle. Never use carb cleaner, you’ll get a fire. Use water to find the leak. Poke a small hole in a water bottle cap and squirt all the suspect places. When you hit the leak the engine will misfire. Much safer than carb cleaner or anything else that can cause a flash fire. Carb cleaner is not as accurate also. The fumes build up and will suck into the leak making it harder to pinpoint the leak.

 

[Nimbley]

Start the engine then spray carb or TB cleaner at the various points where the vacuum could be leaking from.

Agree about the vac leak but this is just bad advice. Seen too many fires this way. Always use water to find the leak. More accurate and less dangerous.

 

[Jerry Bransford]

Agree about the vac leak but this is just bad advice. Seen too many fires this way. Always use water to find the leak. More accurate and less dangerous.

I couldn't disagree more with your warning. What I described is a common and time honored method of finding vacuum leaks. Of course it's flammable but so are many of the products we use around engines. If you and your buddies can't do this without causing fires you all need to put your tools away and find something else to do with your time. Any well equipped shop should have a fire extinguisher but in 50+ years of using carb and throttle body cleaners around running engines I've never had a single fire or any other problem. A little common sense goes a long ways in not having problems.
But if you can't use it without causing fires don't use it. Just don't claim the procedure is too dangerous. It's widely used without problem. Though I will admit some people can't cut a board in half without injuring themselves. For that person I'd tell them to avoid anything that is more dangerous than watching someone else do the work.

The bottom line is if you can't use the recommended method without catching something on fire don't do it. Not everyone has that inability though.

https://www.oldcarsweekly.com/restoration/make-vacuum-leaks-hiss-tory

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

https://www.liveabout.com/engine-vacuum-leak-symptoms-4174856

 

[Nimbley]

It’s not a case of me and my buddies can’t use it correctly. In fact I find that comment insulting. I’m a professional with over 25 years experience. It’s always the guy that’s been doing it forever that is stubborn in his ways that causes the fire. And I’m sticking with that other point also. Water is always more accurate at finding leaks.

 

[Steel City 06]

Consider the DIY smoker to find leaks:

https://wranglertjforum.com/threads/cheap-engine-vacuum-leak-tester.19643/

 

[bobthetj03]

We had a smoke machine at work, so we smoke tested it. Smoke poured out of the throttle body shaft at both ends. Not sure how sealed that shaft is supposed to be, but it made the test inconclusive.

 

[Nimbley]

We had a smoke machine at work, so we smoke tested it. Smoke poured out of the throttle body shaft at both ends. Not sure how sealed that shaft is supposed to be, but it made the test inconclusive.

I’d call that pretty conclusive. Throttle shaft bushing are the source of your manifold vacuum leak. You can have the throttle body bushings replace and that should take care of your leak.

 

[bobthetj03]

Where would I source the shaft bushings? I thought they were roller bearings with a teflon seal on each side of the bearings?

 

[Nimbley]

I send it to the local machine shop. They re bore the holes and press in new bronze bushings. Not something you really want to attempt unless you have to proper tools. Should be about $50-60 if you pull the throttle body yourself and take it to a shop. Between carburetor rebuilds and throttle bodies I send in several a month.

Yes I said carburetors. Not many shops around anymore that’ll rebuild them but I still do quite a few. In this area of the country we still have a lot of older cars on the road.

 

[ballpark]

Mine did this and it was the idler pulley

 

[bobthetj03]

Mine did this and it was the idler pulley

I've had that happen and changed it along with the tensioner assy.,as well as the alternator when it started squealing.

 

[Mike_H]

Any Luck @bobthetj03? I noticed a whistle the last few times I drove, at idle when its cold. Thinking throttle body or IAC. This morning, the jeep didn't want to run without a couple of quick stabs at the accelerator pedal.