Chasing a vacuum leak (1 Viewer)

[mwebfj60]

I've been searching for a 1 inch vacuum leak about a week...slowly checking all the normal culprits...finally went to pull the valve cover to check valve lash thinking maybe it was causing 19 1/2 and the PCV pulled out really easy. I had wiggled it around while the motor was running to see if there was any change a few days ago and nothing. Just got this thing about 3 months ago from the local Toyota dealer. Put the old one back in (I'm a bit of a parts hoarder) and back to 20 1/2.

 

[4Cruisers]

Put the old one back in (I'm a bit of a parts hoarder) and back to 20 1/2.

View attachment 1537458

Aren't we all?

 

[Landpimp]

I think there are 2 styles of PVC grommets, one is better than the other maybe....I had both types, think I used the one you show.

I may be wrong and the other was for my 82 fj40...but that should be the same as a 60.

 

[OSS]

The leak was likely at the hose to PCV junction at the top of the valve or the sticking PCV valve itself...not the grommet.

The PCV valve can be completely removed from the side cover fitting (& grommet) with its top PCV hose attached and it won't reduce the manifold vacuum at all. The only vacuum leak that can occur down near the PCV valve is the hose connection at the top of the valve or the PCV valve itself.

That's why it doesn't matter if the PCV grommet is loose or hard as a rock with poor fit. It's the valve itself (and the hose connections above it) that control the vacuum.

 

[mwebfj60]

@OSS Why do you have to come in and rain on my parade with all these facts and logic! I had always thought there was still vacuum pulling through the PCV at idle. Thanks for the heads up. Now when I get home I have to put the gauge back on and pull the PCV to settle it in my mind.
On a side note, I did have the HIC valve out when I pulled the air cleaner to check it and the HAI diaghragm while working my way to the valves. Both checked good. I also tightened the hose clamps on both sides of the PCV T and on the PCV valve. So maybe this sealed up the leak.

Thanks!

 

[OSS]

Ha!

Since this is a Vacuum Leak thread, I'll throw this info out for others who might stumble upon it during search-

These are the factory 'normal' small metered vacuum leaks that were designed into the 2F vacuum hose extravaganza that should always be present on a stock, smog legal engine:

1. PCV system
2. EVAP system while driving (not at idle)
3. EGR system while driving (not at idle)
4. HAC system at any altitude
5. Choke Opener system
6. HIC valve. Small leak when cool, bigger leak when hot.

The sum total of these were accounted for by Toyota in the sizing of the carburetor jets. When all is right & working as it should, over 20 inHg of vacuum should exist in the manifold at idle on a warmed up engine (but not blazing hot) at sea level.

Also running a hot engine without the big cool air intake duct connected to the air cleaner housing neck (have seen lots of pics on mud of engine compartments missing this duct) will increase the temperature of the air getting sucked into the air cleaner which will open the HIC valve farther, which will create a slightly lower manifold vacuum reading.

Sneaky vacuum leaks that shouldn't exist can also be found in the old VCVs for the distributor venting & EVAP at pipe S on the valve. Also almost all old EGR valves leak a little bit even when closed and its rare to find one that seals perfectly tight.

And of course the usual culprit of manifold mayhem.

....but I think you've got all those accounted for.

 

[mwebfj60]

The leak was likely at the hose to PCV junction at the top of the valve or the sticking PCV valve itself...not the grommet.

The PCV valve can be completely removed from the side cover fitting (& grommet) with its top PCV hose attached and it won't reduce the manifold vacuum at all. The only vacuum leak that can occur down near the PCV valve is the hose connection at the top of the valve or the PCV valve itself.

That's why it doesn't matter if the PCV grommet is loose or hard as a rock with poor fit. It's the valve itself (and the hose connections above it) that control the vacuum.

Good call. Pulled the PCV valve out at idle and it only dropped vacuum by a little over a 1/4".

 

[mwebfj60]

I think there are 2 styles of PVC grommets, one is better than the other maybe....I had both types, think I used the one you show.

I may be wrong and the other was for my 82 fj40...but that should be the same as a 60.

The old OEM one was different than this OEM one. Should have taken a side by side. This newer one was a lot softer than the older one when it was new.

 

[mwebfj60]

@OSS , I have a different understanding of a couple of the systems...
The choke opener shouldn't be a vac leak as long as the diaghragm is good. Gas filter to BVSV to diaghragm.

The HAC stops being a vacuum leak at altitude, again, as long as the secondary diaghragm holds vac. That's the function of the T in the system. Once that vacuum port on the HAC closes, the vacuum builds up in the line to pull the diaghragm. The check valve is there to maintain vacuum when the motor is shut off so timing is advanced for startup. Once altitude is dropped, the vacuum port on HAC opens to atmosphere to release the vacuum.
The HIC should be a passthrough for vacuum to pull the HAI diaghragm when engine is cool. When engine is hot, the vacuum side from the PCV T is closed and the HAI diaghragm side is open to atmosphere/air cleaner to let the cool air intake operate. The HAI flap pulls up by vacuum applied to the HAI diaghragm.

Edit...The HIC does open the vacuum side to the air cleaner when hot.

Take me back to school bud.

 

[OSS]

Not sure about school, but I'll settle for some entertainment---

Some vacuum systems on the 2F use small continuous vacuum bleed lines in the routing to allow the release of vacuum when the state of that system changes (on/off).

These designed vacuum bleeds are small, and should be there, but they all add up.

1. Choke Opener-
That little mysterious white plastic doo dad inserted in the middle vacuum hose leading up to the air cleaner breather pipe is a bleed off orifice (doo hickey might be a better word) for the vacuum supply to the CO. You can see it in the schematic of the CO circled in red. It's a tiny leak, but continuous. Its purpose is to assure that the CO doesn't get stuck open, preventing the choke from working if some sort of weird obstruction occurred in the vacuum line going to the CO after it was actuated. If that unlikely event happened, the choke would be inoperable and a person could conceivably not be able to start the engine on a cold morning. They would be stuck up in the mountains, unable to leave & would eventually starve to death after they ate each other after drawing straws.

So that little plastic doo hickey with its tiny vacuum leak could save someone's life.

On to the next one:
2. HIC Valve.

On a stock 2F with all emissions equipment installed & working properly, the HIC valve is always in a state of movement on a non hot day, (below 92°F) constantly opening & partially closing, modulating between states of too hot & too cool, trying to keep the air temperature going into the air cleaner housing at a comfy 81°-91° temperature. This valve controls both the hot idle compensation by allowing some extra air into the manifold (vac leak) at hot idle -and- the HAI (hot air intake) flapper valve located on the air cleaner neck.

The air getting sucked past the exhaust manifold is mighty hot going up through the HAI valve so once the HIC valve gets some of that blazing heat, it closes back down, which then released the HAI flapper valve. This all happens kinda in slow motion since the HAI valve is slow to change to temperature.

The only way the HIC valve can close the HAI flapper is to be able to bleed off vacuum to it. And so it does. There's a small designed vac bleed off going through that valve while the engine is running. Without the vac bleed, the HAI flapper would get pulled and then stay open as long as the engine was running. The engine would probably overheat & blow a head gasket & leave the passengers of the car stranded in the wilderness where they would runout of food & eat each other after drawing straws.


Familiar drawings to us, posted here for others to refer to.

On to the last one
3. HAC System
This system too uses a continuous vacuum bleed off to release the outer vacuum actuator on the distributor. A little air (vacuum) is constantly being pulled through the bottom port of the HAC valve at any altitude. At low altitude it's a small designed parasitic vacuum leak going straight into the intake manifold, at altitude, a lot more air gets sucked up through the bottom of the valve into the carb to lean out the mixture. It's a vacuum leak too. Just an intended one for altitude.

The schematic in the FSM doesn't show this, but the testing section in the emissions FSM reveals it. If you check an old filter in the bottom of the HAC valve, you'll see that it's pretty dirty even if you never go to altitude. That's because a bit of air (vacuum) is always flowing through it.
If this designed continuous small vacuum bleed wasn't present in the HAC system, the HAC vacuum advancer on the dissy would get pulled at 4000 feet and wouldn't let go until the engine was shut off.
This could lead to the death of the passengers in the car...

Because....

When the passengers in the car drove down from the mountains from their glorious thanksgiving holiday with family & friends, the HAC vacuum advancer wouldn't disengage as they descended into Death Valley. The engine spark advance would be much too far advanced (6°) for that elevation below sea level and the engine would detonate severely. But since they had the radio turned up so high, they couldn't hear the pinging and the engine then would overheat and blow a head gasket... leaving them out in the wilderness in the middle of Death Valley with no food or water or cell phones. So once again, after a few days, these poor people would run out of food & eat each other after drawing straws.

But this time - they tasted like turkey!

Here's some minutiae I drummed up from my retired screen name.

High Altitude Comp (HAC) Valve

1987 FJ60 High Altitude Compensator (HAC) Routing

 

[mwebfj60]

Good stuff,
Now we know what the little doohickey is. Makes sense if the BVSV failed and stuck closed while vacuum was on the CO.

When the HIC valve opens to atmosphere, it isn't opening the vacuum side to atmosphere just the HAI diaghragm side to release the vacuum and drop the flapper back down. The vacuum side is closed and that port holds vacuum at that time. Technically you could call the cycling a vacuum leak as it has to suck the air back out of the 20" of tubing each time it cycles but the vacuum port itself should never be open to atmosphere unless the HIC valve is bad.

Good call on the HAC, I never thought of the 3 ports at altitude being a vacuum leak but technically the primary slow is a ported vacuum. The primary and secondary plumbing in above the venturis no but the primary slow yes. That doesn't have anything to do with releasing the vacuum from the advancer though. The only way that happens is when the bellows contract and open the vacuum port back to atmosphere so it can bleed off.

Now that you mention it, a turkey dinner sounds pretty good right now.

Thanks for the knowledge OSS.

 

[OSS]

The HAC plumbing is deceptive (sneaky engineers). Take a look at the HAC vacuum flow diagram below.

1. The vacuum source starts at the gas filter fitting in the intake manifold. That's the beginning.
2. Then it goes by a check valve.
3. Then it has connection to the vacuum advancer on the distributor
4. Then, finally it ends up inside the HAC valve.

There is always a vacuum potential connected to the distributor advancer when the engine is running. The only reason the distributor vacuum advancer doesn't get pulled at low altitude is because the vacuum is constantly being bled off (released) inside the HAC valve, creating a small vacuum leak from the bottom of the valve through that dangling hose.

The first drawing shows the circuit at altitude with the advancer pulled. The only way to release the advancer is to constantly bleed the vacuum.

As to how significant that vacuum leak is, I've never tested it. It's probably barely detectable with a vacuum gauge connected to the manifold at idle. Don't know. It would be easy enough to plug the bottom of the HAC valve at low altitude w engine idling & see if manifold vacuum increased a tad. I'd be interested to know if it was detectable with a MityVac.

 

[Spike Strip]

Good info, OSs -

I always thought the little plastic thing for the CO was just a check valve -- where did you read that it's a vacuum bleed ?

Admittedly, I never looked very closely at it.

 

[OSS]

Sorry @mwebfj60 to trample all over your thread. I've learned good stuff from your posts in the past. It just seems that this thread looks like a good place to put this stuff.

To answer spike's question, vacuum restrictors are not well documented except for the tiny black triangles ▸ ◂ marked on the vacuum schematic and by very close examination of the drawings in the emissions FSM. I've circled them in red in the drawing below. Check-valves are green.

There is a vacuum restrictor built into port P of the EGR modulator to slow down the actuation of the vacuum pulling the EGR valve. You can see it referenced on the schematic and barely make it out in the drawing.

Another vacuum restrictor ▸ ◂ is at the HAC port in the carb to reduce the flow of air getting sucked in the carb at altitude. And that white plastic CO restrictor thingy near the air cleaner is one too. You can blow air through it (barely) on either end.

Toyota calls the white plastic CO thingy a "standard part" but all the check valves that are really check valves (one way valves) are called 'check valves' by name and are labeled as check valves on the schematic.

This is definitely vacuum minutiae that 60 owners normally never need to know about, but if a person were mucking around with the spaghetti nightmare under the hood, yanking hoses willy nilly, these little vacuum details could maybe be important.

 

[mwebfj60]

This is good tech and will come in handy soon as it looks like Kalifornia is going to be the permanent residence and I'm going to have to re-smog and re-recurve in the fairly near future. I'm sure I'll be hitting you up for more of this minutia.

 

[Spike Strip]

So you think those things are just 'restrictors'? and have no 'one-way' function? Asking cuz I'm seeing if there's anything available aftermarket or from other Toyota applications since those doohickys are disco'd.

 

[mwebfj60]

The HAC leaks right at 1/4" of vacuum at low altitude.

 

[OSS]

So you think

I'm (pretty) sure that white doohickey used for the CO inline w the vac hose leading up to one of the three air cleaner pipes isn't a one way check valve. It would be easy to find out for sure though--- remove it & blow air through both sides. If the resistance is the same both ways, then it's a restrictor. If the air flow is different, like a big plastic VTV, then I'll eat my iPhone .. with tobasco.

 

[OSS]

The HAC leaks right at 1/4" of vacuum at low altitude.

Since you're testing (ha!) how far does the vacuum drop when the AC idle up hose is pulled? (normally connected to the pipe jutting off the brake booster fitting).

That's considered a big vac leak. My engine doesn't sound happy if I pull that hose & let that fitting suck atmosphere.

 

[mwebfj60]

Since you're testing (ha!) how far does the vacuum drop when the AC idle up hose is pulled?

With the vac gauge on the gas filter it didn't register a change by pulling the AC idle up hose. With the gauge on the AC idle up port, pulling one of the lines off the gas filter dropped the vac by almost an inch.

I think I would need to run a T off the AC idle up to get a better reading on it and don't have a spare one.