Solved: Hard vacuum leak under DECELERATION

[STI_MECE]

Okay so no idle fluctuation, hesitation or anything. Driveability is great. But, I hear something on the drive side of the engine. Every time I am on the highway, and let off the throttle I hear a vacuum noise. To be more transparent about it, it sounds like air is being sucked through a hole and the whole is increasing in size since it's now making the noise at lower speed.ive tried taking videos of it because the noise frequency is so low it's hard for my phone mic to pick it up.

I've smoked it, I've replaced every damn hose in existence.
Nothing shows up.

My ideas of where the noise could be coming from. Either back of the valve cover on drive side around the moon plugs. Maybe there is a pocket of gunk somewhere that is drawing air in. Or it's the EVAP canister.

Help me get this annoying noise fixed!

A week ago it would only do it when I'm going above 60mph AND let off the throttle.

Now it's doing it at anything above 40 mph.

 

[wcjeep]

Evap smoke machine?

What is the condition of your vacuum lines? On a previous non Toyota vehicle I replaced every vacuum line due to age. On a diesel truck I used small zip ties at every vacuum connection to eliminate the leak. Today I'd probably use an evap smoke machine.

 

[brillo_76]

Did you try the carb cleaner trick in your engine compartment? Used to find vaccum leaks on cold engines that way. When you hit whatever leaking it mostly increases the idle. Carb cleaner is flammable and evaporates fast so if you do decide to do that. Be careful. :]

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[STI_MECE]

I made a home made smoke machine. Glass jar, baby oil, sock and a bicycle pump. Then I connect to the throttle body.

Then pump smoke into the engine. I saw no smoke come out anywhere.

I've ran this test before hand and replaced hoses where I did see smoke come out.

Like I said this is a HARD vacuum leak. My bike pump obviously can not build enough pressure to fine the leak.

There is more vacuum on the engine coasting at 60 mph than there is at idle.

This is really my last little annoying thing about this truck before its more or less back to normal.



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[pluton]

Look at and around the vacuum booster?

 

[HiLife]

Sound like the vacuum is on a switch, only coming on in a de acceleration state. I say the issue is somewhere around the fuel evap canister.

 

[STI_MECE]

I think I figured it out.

My oil cap doesn't have a rubber gasket around it

I noticed the part diagram this morning of it. I am amazed there isn't lol leaking out of it. But I sure as check hope that's it.

2 dollars at dealership get it tomorrow! Fingers crossed that's it.

Will have to wait till Thursday to test. Rebuilding rear brakes. Cylinders, pads, and drums. One side down.

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[brillo_76]

I think I figured it out.

My oil cap doesn't have a rubber gasket around it

I noticed the part diagram this morning of it. I am amazed there isn't lol leaking out of it. But I sure as check hope that's it.

2 dollars at dealership get it tomorrow! Fingers crossed that's it.

Will have to wait till Thursday to test. Rebuilding rear brakes. Cylinders, pads, and drums. One side down.

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I never seen the oil cap seal missing on any toyota before. That would be a new one. I can understand why you be scratching your head. Who wouldn't replace a rubber gasket on the plastic oil cap if lost. Also why would it be missing to begin with in the first place as I dont see how those fall off. Very interesting to say the least.

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[STI_MECE]

I never seen the oil cap seal missing on any toyota before. That would be a new one. I can understand why you be scratching your head. Who wouldn't replace a rubber gasket on the plastic oil cap if lost. Also why would it be missing to begin with in the first place as I dont see how those fall off. Very interesting to say the least.

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Well if you have seen my build thread you would understand something like this missing on my 4runner is totally possible.

The PO was absolutely incompetent and I am the idiot who took the bait. He even took a angle grinder to the front spindles so they wouldn't rub on the shocks. With this being my first runner. The only positive is I only got 2WD. So that is alot less stuff I would have had to fix! Lol maybe my next go around I'll get a 4x4.

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[brillo_76]

Well if you have seen my build thread you would understand something like this missing on my 4runner is totally possible.

The PO was absolutely incompetent and I am the idiot who took the bait. He even took a angle grinder to the front spindles so they wouldn't rub on the shocks. With this being my first runner. The only positive is I only got 2WD. So that is alot less stuff I would have had to fix! Lol maybe my next go around I'll get a 4x4.

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:/ Lots of Mr Goodwrenchs out there that really should leave things alone. :[ We have so many build threads on here its impossible to keep track of them all. I hope this solves it for you. . I go back to the 80's pickup mini pickups as a had several of those in the 90s. Never seen one even bad deterated or missing. Look at all.the fun your having

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[brillo_76]

:/ Lots of Mr Goodwrenchs out there that really should leave things alone. :[ We have so many build threads on here its impossible to keep track of them all. I hope this solves it for you. . I go back to the 80's pickup mini pickups as a had several of those in the 90s. Never seen one even bad deterated or missing. Look at all the fun your having

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[19963.4lsr5]

I think I figured it out.

My oil cap doesn't have a rubber gasket around it

I noticed the part diagram this morning of it. I am amazed there isn't lol leaking out of it. But I sure as check hope that's it.

2 dollars at dealership get it tomorrow! Fingers crossed that's it.

Will have to wait till Thursday to test. Rebuilding rear brakes. Cylinders, pads, and drums. One side down.

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If you have the factory oil cap the seal shrinks and gets hard as nails. It’s fun digging out. And aftermarket oil cap from say NAPA is a simple flat piece of rubber.


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[brillo_76]

If you have the factory oil cap the seal shrinks and gets hard as nails. It’s fun digging out. And aftermarket oil cap from say NAPA is a simple flat piece of rubber.


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Yes it gets very hard. So someone had to actually remove this gasket and just leave it off. :/ Like the OP states. He knee deep in this one and the PO was an extremely bad Mr Goodwrench... I just never saw anyone actually do that. It's one of these wow why would mess with that moments.

Also with bizarre things like that. I would wonder what else they messed up. I go find the build thread for this rig as now I am curious.

I would either get a used OEM from a junk yard or buy a new gasket / cap from Toyota.

The OP is in the case though. Soon all his work and fixing will pay off.





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[STI_MECE]

So the gasket is on and about 75% of the noise is gone now....wooooo

Its still there. The cap is on tight but I can still pick up the same noise.

And now when I push the brakes I can kind hear alittle tonal difference like there may be something around the booster area.

I think my upper intake manifold is an aftermarket one. I should have taken the picture of why I think that butttt I will be doing valve covers after the timing belt job so I'll fix that up next

I can turn the music up louder the noise now so it's good lol it drives great after swapped the TPS sensor.

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[STI_MECE]

It's back lol

So the oil gap gasket didn't solve the issue. Which now I think about it doesn't surprise me.

There is an aftermarket brake booster on my car. And because of the stupidity of PO. I know there is supposed to be a gasket between master cylinder and the brake booster interface.

So I backed off the master cylinder and sure enough.....no damn gasket. I looked real close and carefully tried to pick at the surface to make sure I wasn't missing the gasket but it's not there.

Maybe that is the issue? I'm gunna beg my dealership for another employee discount lol hopefully it no more than 5 bucks.

But maybe that might be because at high speeds sometimes my brakes are alittle soft. And when at low speeds 30 and below the brake pedal progression is normal.

If this doesn't solve the issue I'm going to buy the OEM check valve, hose, clamps and grommet and pray that stuff will fit in the aftermarket booster.

The price of the OEM booster is obscene.

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[LittleCaesar]

Hunts the yards for an OEM one. Usually are priced between $10 and $30. I would like to think that the missing gasket is your problem but this Toyota has a real hard time using most anything but OEM parts.

 

[brillo_76]

It's back lol

So the oil gap gasket didn't solve the issue. Which now I think about it doesn't surprise me.

There is an aftermarket brake booster on my car. And because of the stupidity of PO. I know there is supposed to be a gasket between master cylinder and the brake booster interface.

So I backed off the master cylinder and sure enough.....no damn gasket. I looked real close and carefully tried to pick at the surface to make sure I wasn't missing the gasket but it's not there.

Maybe that is the issue? I'm gunna beg my dealership for another employee discount lol hopefully it no more than 5 bucks.

But maybe that might be because at high speeds sometimes my brakes are alittle soft. And when at low speeds 30 and below the brake pedal progression is normal.

If this doesn't solve the issue I'm going to buy the OEM check valve, hose, clamps and grommet and pray that stuff will fit in the aftermarket booster.

The price of the OEM booster is obscene.

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Unreal.. Eventually, you will have everything fixed. Since the oil gasket is missing. You may find a few more interesting gaskets missing. :-(

 

[STI_MECE]

I'm at wits end I tried a gasket from O'Rileys just for shiggles. That's not it

I'm going to jack the rear end up next week and drive the car with the wheels spinning in the air.

That should do the trick to let me stick my head under the hood and see what is happening while the vehicle is at speed.


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[AntleredRuin]

FWIW, as long as it's meant for the 4Runner, an aftermarket brake booster won't matter. Obviously has to be in good working order, etc.
A guy who posted a few months ago had good luck with a $50 eBay special. I'm running a $300 Advanced Auto Remanned, no problem.
And with a lifetime warranty, better $300 than like $800 for an OEM.

If it does have an aftermarket intake manifold, and the guy was notorious for not using gaskets, I might check there. You could have a hell of a vacuum leak under the manifold.

 

[STI_MECE]

FWIW, as long as it's meant for the 4Runner, an aftermarket brake booster won't matter. Obviously has to be in good working order, etc.

A guy who posted a few months ago had good luck with a $50 eBay special. I'm running a $300 Advanced Auto Remanned, no problem.

And with a lifetime warranty, better $300 than like $800 for an OEM.



If it does have an aftermarket intake manifold, and the guy was notorious for not using gaskets, I might check there. You could have a hell of a vacuum leak under the manifold.

Yeah you raise a good point.

My booster DOES work and no obvious leaks. I just cling to it since it's the only thing I can do without ripping into the intake manifold. Lol
I am missing that bracket that pressed against the check valve. I'm gunna try and scope tht up at the junk yard.

I do have an oil leak I think it's coming from the half Moon on the driver side. But I could never see if anyone had a leak bad enough to have an audible leak coming out of there.

I'm trying to hold off on the valve covers for weeee bit. Starting my timing belt job tomorrow, I got a laundry list of stuff to do. Gunna take me at least a week to get it done.





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