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Thread: What does a particular VSV do? See excellent attached diagram.

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    What does a particular VSV do? See excellent attached diagram.

    So there is this VSV on the passenger side of the engine bolted to the side of the head that takes a vacuum from the intake manifold and switches that vacuum to the fuel pressure regulator. And this interesting attached diagram shows that there is a variation of the system where it is NOT present, see the box in the diagram that says W/O COOLER. So can someone please explain this to me? What cooler? I thought fuel pressure was regulated by the ECU maybe telling this VSV to switch on or off. Or does simple direct manifold vacuum control fuel pressure, and the VSV disables that when the cooler is in the system? Also, if the intake manifold has filtered air already, then why is there a filter (part #23265) needed? To keep the VSV from gumming up maybe? By the way, all these issues are because my 1987 van with 4YE does feel as zipping as my 1984 with a 3YE.

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    Re: What does a particular VSV do? See excellent attached diagram.

    It seems like my diagram gets shrunk when I post on the forum, sorry about that.

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    Re: What does a particular VSV do? See excellent attached diagram.

    Also, does anyone have the part number to the filter that threads into the intake plenum that connects to this vacuum line I am talking about? The diagram shows it as part number 23265 but why does it only show 5 digits I wonder...

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    Re: What does a particular VSV do? See excellent attached diagram.

    I'm not sure why............perhaps it's because it's a png file and the forum automatically converts to jpg? Regardless, I edited your post to display full size. That VSV (EFI VSV) is part of the system designed to combat hot soak. It would be easier to understand if you read through the "HOT SOAK" thread 1st, but I'll elaborate a bit here.

    Basically the van has a bit of a challenge when it comes to dissipating heat from the engine compartment. Now add a hot day, a steep hill and the problem becomes exasperated. As long as everything is in tip top shape and the van remains running, no problem. Now add an air conditioner (more heat) to the system, & heat related problems ensue. The particular problem the EFI VSV is there to combat is Heat Soak. As long as the van remains running heat soak issues are kept at bay, but when you shut the van off, the loss of venting (fan) & coolant circulation further complicate things. This extreme heat with no place to go soaks into the fuel rail causing the fuel to boil/vaporize (resulting in a vapor lock condition). The problem is realized when you try to restart the van. It's mostly annoying & embarrassing, but also takes a toll on starter life. The van will start & stall, requires excessive starter cranking, runs rough, and the exhaust stinks. This lasts about 1 - 2 minutes then goes away. This was a problem back in the 80's when Gasoline had higher boiling temps, but is even worse with today's gasoline.

    Okay, so here's where the EFI VSV (AKA Pressure-up VSV) comes into play. On each start up the ECU checks an engine temp switch (only on vans equipped with AC). If the switch is closed (happens at 230 deg F) it knows there's a potential heat soak issue. When a hot soak condition is detected the ECU activates the EFI VSV. When activated this VSV prevents manifold vacuum from reaching the FPR (Fuel Pressure Regulator). When vacuum is removed from the FPR the fuel pressure jumps from ~30psi to ~40psi. This increase of pressure reduces the potential for fuel boil (more pressure = higher boiling point). The ECU activates this VSV for only about 2 minutes, as this is enough time to offset the problem until restored coolant circulation & air ventilation can resume/reduce engine temperature. When the 2 minutes are up the ECU cuts power to the VSV, vacuum returns to the FPR, fuel pressure drops, and the ECU will not monitor the temperature switch again until the next time the van is started.

    So this was the plan, but perhaps they underestimated the effects of hot soak. A changing fuel market certainly hasn't helped matters. It wasn't long before Toyota realized this was a bigger problem than originally anticipated. They responded by replacing the 230 deg F temperature switch with a 140 deg switch, but they only did this on vans that came into the dealer with chronic hot soak issues. Most vans never got this new switch (which is now NLA). In the "hot soak" thread we discuss alternate methods to help combat this problem. Tim

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    Re: What does a particular VSV do? See excellent attached diagram.

    That filter is Toyota part #90917-11022. It's not there to prevent dirt from getting in the VSV it's there to keep things out of the intake manifold. Not sure why it's necessary unless they're anticipating a failure (like the FPR diaphragm or something).

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    Re: What does a particular VSV do? See excellent attached diagram.

    Quote Originally Posted by robgagnon View Post
    And this interesting attached diagram shows that there is a variation of the system where it is NOT present, see the box in the diagram that says W/O COOLER. So can someone please explain this to me? What cooler?
    "COOLER", in this case, refers to the A/C. So if your van did NOT come equipped with air conditioning, it has the "W/O COOLER" variation.

    Gwen
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    1989 4WD 5-speed DLX; 410K and an odd sense of humor ("Skylervan")

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    Re: What does a particular VSV do? See excellent attached diagram.

    That was a GREAT explanation Tim, I completely get it now. That also make me think I better hurry up and get that filter: the tip broke off and the filter has a bit of glop on it to plug the hole and the vacuum hose has a golf tee in it. This is how I got the thing, and my 1984 also has a similar fix (but it runs great). So therefor I am running too high a fuel pressure which would cause a too rich condition.

    Also: it seems to me that for a van that has heat soak issues chronically, one could introduce a push button switch connected to the fuel pump tester connector and if you had an issue and just activated the fuel pump for a bit of time, it would push to the too hot fuel down the line back into the tank, but I might not be thinking correctly.

    Thanks much.

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    Re: What does a particular VSV do? See excellent attached diagram.

    Having higher fuel pressure won't make it run rich as the ECU will compensate by cutting back the firing time of the injectors (it adjusts injectors based on the input from the O2 sensor). If however the O2 sensor had failed, the ECU would be in the "limp" mode (already rich), then yes, having no vacuum on the FPR would make it run richer. Your idea on activating the fuel pump before cranking might actually work, but IMO it's somewhat taboo to mess with these systems (potential safety issues). I prefer ventilation as a solution. Keeping the engine bay cooler will also prolong the life of your hoses & little plastic parts. Tim

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    In the diagram, what does the VSV and the diaphragm with the adjustment screw do?

    And when does it do it?

    I am talking about the "pair" of devices on the passenger side of the intake plenum.

    It would appear to me that the VSV is controlling a diaphragm operated valve which is also in essence a VSV, but rather than be a solenoid triggered valve it is a vacuum triggered valve. And that diaphragm valve has a larger hose on it suggesting that the need for a higher RPM boost was wanted by the designers. But when does the VSV activate and why, and is there any reason to ever adjust the screw on a diaphragm?

    Thanks!

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    Re: What does a particular VSV do? See excellent attached diagram.

    The diaphragm when activated increases engine idle speed. It can be activated via that VSV (which is activated with the AC compressor). The other way it's activated is via the power steering pump. There is a vacuum valve on the power steering pump called the "air control valve" (it's the one marked 17630 in the lower left corner of the diagram posted above).

    Example: Lets say you're in a parking lot at an idle. Now you start cranking the steering wheel. Steering the front wheels on a hard surface without the vehicle rolling takes a bit of energy (enough to stall the engine). Exerting such energy causes pressure in the pump to spike. This excess pressure opens the "power steering air control valve" which allows vacuum to flow from the manifold to the idle-up diaphragm. The diaphragm changes position and the result is increased idle speed (enough to compensate for the load and prevent engine stall). There is an adjustment screw (plastic bolt sticking out the side with a spring on it). This screw is used to set the idle speed while the diaphragm is in the "idle-up" mode (typically set while the AC compressor is running & the "idle-up" system is activated). Tim

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    Re: What does a particular VSV do? See excellent attached diagram.

    Let's call these VSVs by name:
    1) VSV fuel pressure regulator controller
    2) VSV RPM Increaser

    And then there is a 3rd VSV which is over by the air filter, and that I believe is commonly called the ISC VSV or Idle Speed Controller, which in your own words somewhere "increases RPM by about 100" as I recall.

    Then there is the 4th VSV which is part of the pair for VSV #2, and would call that an Vacuum Amplifier if I were naming it because it seems to provide a more hefty amount of air bypass than just the electric VSV can do, on account of the increased hose size.

    So is there ever been a reason to change the screw setting on this VSV #4? What are some of the effects of a bad VSV #2 or #4? Some people talk about too high an idle, in other threads. I would think a faulty diaphragm in #4 could cause all kinds of idle issues, or a stuck open VSV #2 could perhaps cause high idle.

    I am going to modify the vacuum diagram I posted above to remove all the part numbers and instead have descriptions of what the components do and it will be much easier to read. I just want to understand the system before I post anything wrong, and of course you can review the diagram for correctness.

    Thanks - Rob

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    Re: What does a particular VSV do? See excellent attached diagram.

    Tim,

    Per the electrical schematic for 1987, you have the following VSVs:

    - EFI VSV
    - ISC VSV
    - AC Idle Up VSV

    The AC VSV is clearly connected to the AC Amplifier (the computer for the AC). It is also connected to the EFI computer. There is no reason why both devices cannot drive the same VSV. I believe Tim said that the AC VSV operated for about 2 minutes upon start up, but I would not be surprised to learn that the AC Amplifier also activates the AC VSV when the AC compressor is engaged, otherwise you might stall out the engine. This is the same idea as increasing horsepower when the power steering is active, of course.

    The EFI VSV and the ISC VSV are controlled solely by the EFI computer.

    That's about as far as I can get without probing the ISC and EFI cables with LEDs leading to a place where I can actually see them might under what conditions. I could also disconnect the connectors and see how it degrades the performance.

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    Here is an annotated diagram

    Name:  Toyota Vacuum Diagram annotated.jpg
Views: 10461
Size:  93.3 KB

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    Re: What does a particular VSV do? See excellent attached diagram.

    The factory service manual refers to the VSV (top right in your diagram) as both the "EFI VSV" and/or the "Pressure-Up VSV" (depending where you look). I personally like the term "Pressure-Up VSV" because that's exactly what it does. The one shown lower right of the diagram is ISC VSV (Idle Speed Control Vacuum Switching Valve). This is also a good name. The one that controls to the diaphragm is simply called VSV but the AC section schematics refer to it as the "Idle-up VSV". That diaphragm is also referred to as "Idle-Up Diaphragm". After reviewing the AC schematics I think we should call this VSV "AC Idle-Up VSV" but continue calling the diaphragm "Idle-Up Diaphragm" (because it's also activated by the power steering pump).

    Since we're on the subject of Toyota changing terminology, I found several references to the 230 deg F temp switch that's part of the hot soak pressure-up system. Here are some of the names I found: "Idle-Up Temp Switch", "Water Temperature Sensor", and "Switch, Water Temp". I'm sure I could find more names for these things if I looked. I wish they would stick to single names as changing terminology only serves to confuse .

    Here's some snap shots I took from the manual. If you look closely, you can see each one has it's own characteristics (nipple configuration & length/shape of body). The diagram you posted shows enough detail to match these up.







    In addition, here's another interesting schematic I found that may help enlighten:


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    Latest Diagram

    Tim,
    Name on VSVs changed - suggest deleting previous diagram.Name:  Toyota Vacuum Diagram.jpg
Views: 12662
Size:  95.9 KB

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    Re: What does a particular VSV do? See excellent attached diagram.

    The part you have labeled "Temperature Valve" is better known as the BVSV (Bimetal Vacuum Switching Valve). It's also known as the "Oh crap I broke it Valve" because the plastic nipples get brittle and break off if you look at it wrong .

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    Vacuum switches and hose diagram

    Updated.
    Name:  Toyota Vacuum Diagram.jpg
Views: 12890
Size:  92.2 KB

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    Re: What does a particular VSV do? See excellent attached diagram.

    Excellent diagram! Could someone post a picture of the intake/head/block from the passenger side so I can see where all these hook into my intake, etc.? I have 2 of the vsv's mounted, but that diaphragm-21908c-I can't tell where it goes into the head or intake and if it uses air from the head.
    Thanks, Aaron.

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    Re: What does a particular VSV do? See excellent attached diagram.

    AC Idle-Up VSV


    Idle-Up Diaphragm

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    Re: What does a particular VSV do? See excellent attached diagram.

    Thanks so much. So neither of these would keep my van from starting it looks like .

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