What makes the Turbo Kick-in on a 1.8T B5.5 AWM engine?

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Thread: What makes the Turbo Kick-in on a 1.8T B5.5 AWM engine?

  1. #1
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    What makes the Turbo Kick-in on a 1.8T B5.5 AWM engine?

    I like to find out when my Turbo comes in without having to wait for the noise (which it means is ON now). When I posted something on the same the aswers as I understand them point to it comes in period.
    I am sure that must be a trigger from some sensor or combination of sensors that determines that power requirements cannot be met under present non-Turbo operation and opens the :Wastegate valve so the Turbo starts to compress the air and allows fora "more fuel" at a stoichiometric conditions, meaning now more air +fuel have entered the cylinder and more power is generator.

    All I want to know which Sensor(s) are involved in the Kick-in of the Turbo to see while I am driver if I went into Turbo mode or I am still on Non-Turbo, just the volumetric filling of the cylinder by the atmospheric pressure.

    Can someone elaborate or point to that info?
    Thanks

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  3. #2
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    You're misunderstanding how the turbocharger works, but first, the terms "turbo", or "turbocharger", are shortened versions of the original name- turbo supercharger.

    It has at its essence only one moving assembly: two bladed disks on a common shaft. One disk (the turbine) is arranged to be spun by the hot exhaust gases from the engine, which due to the common shaft, spins another disk (the compressor), which does the compressing of the fresh air going into the intake manifold. There is no signal or trigger to make this happen; the more exhaust gas through the turbine, then the more air moved by the compressor. The so-called kick-in occurs when the intake manifold pressure becomes higher than it would be if only atmospheric pressure was available to fill the cylinders. You should also know that the wastegate does not open to start turbocharger boost, it only opens to limit the boost pressure. The wastegate is an exhaust by-pass around the turbine, which limits how much energy the turbine takes from the exhaust flow.

  4. #3
    Motel Room Moderator VAGguy's Avatar
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    To add, the Diverter valve also controls when boost is introduced into the intake.

    Vacuum from the motor at low throttle plate angle (almost closed) holds the spring loaded valve open in recirculate mode and will not let the turbo compress any air in the intake stream. Once the throttle is opened which causes the engine to lose vacuum, it lets the DV close under it's own spring pressure and the always-spinning-turbo then can create pressure within the intake piping. That's when it "kicks in". Older 1.8T was purely vacuum controlled, AUG/AWMs and the like used a solenoid valve to control how much vacuum was sent to the DV fine tuning the onset of boost to better match air/fuel delivery.
    Last edited by VAGguy; 05-16-2019 at 09:54 AM.
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  6. #4
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    Quote Originally Posted by VAGguy View Post
    To add, the Diverter valve also controls when boost is introduced into the intake.
    ... and when I recently replace DV after 18 years, the boost on my car shoot up to the sky.
    VAGguy and samOC like this.

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    Very Good explanation ylwagon, but yourself failed to realize that what kicks in the turbo is as you said: "The so-called-kick-in occurs when the intake manifold pressure becomes....."

    Which gives me the answer and to go and see where and how can I tap into that pressure to know when the manifold gives up its signal.
    Thank you.

    Now I need to figure out how to convert that into a LED that tells me the TURBO starts.

    By the way, in researching that I found something called the "one minute" rule T to ensure a healthy and long trouble free for the Turbo Unit.
    It can be found in a website, but if moderators think is appropriate I can copy it on a posting.

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    I like then to see I can jury-rig a micro switch to tell me when that diverter valve moved enough to get the impellers doing to boost.

    I like that better that trying to guess where in the computer produces a signal and tap into it. Otherwise I may create more damage as I often do.
    Thanks, will look on Bentley, but no hopes they give a clue.

  9. #7
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    Quote Originally Posted by PassatGLS-00 View Post
    Now I need to figure out how to convert that into a LED that tells me the TURBO starts.

    By the way, in researching that I found something called the "one minute" rule T to ensure a healthy and long trouble free for the Turbo Unit.
    You're going about this the hard way, in my opinion. Buy a "boost gauge" AKA manifold pressure gauge, which will be more useful to you than an LED indicator. There is a short hose between the fuel pressure regulator (FPR) and intake manifold which, when cut in the middle and a "T" fitting attached, provides a convenient way to make a connection with the gauge inside the cabin.

    "One minute rule". I assume you mean the idling of the engine for a minute before shut down, to cool the hot turbo. That was recommended for turbochargers without a cooled bearing housing, because when the engine stopped, the oil flow stopped, and heat-soak from the hot turbine wheel would overheat the shaft and could 'coke' the oil. This is less important with your Passat, since it does have a coolant arrangement, so even with the water pump stopped, there will be some flow due to the thermo-syphon effect. You can see the inlet and outlet coolant lines at the bearing housing.

    The diverter valve which VAGguy and Emry mentioned prevents turbo-surge, which can occur when a compressor's pressurized flow is suddenly shut off by the throttle. The diverter valve opens and sends the air back to the compressor inlet, allowing the turbo to dissipate energy without damage.

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    you can run a parallel circuit to the N75 valve which when "charge" is called for , allows turbine pressure which has kept "penny" valve open to close starting the boost cycle/sequence , it is a simple solenoid 12volt valve.
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  11. #9
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    OP, just remember that no matter what you do and how much boost is applied, the turbine inside the turbo will be spinning anytime the engine is running. The controls only affect the pressurized air path not whether or not the turbo is 'on'.
    cchief22 and dihedral like this.

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    Quote Originally Posted by cchief22 View Post
    you can run a parallel circuit to the N75 valve which when "charge" is called for , allows turbine pressure which has kept "penny" valve open to close starting the boost cycle/sequence , it is a simple solenoid 12volt valve.
    While the N75 valve is, indeed, just a simple 12 volt valve, the ECM modulates the power to the valve so that it acts more-or-less as an analog valve, i.e. it can be partway open as needed. If you connected a voltmeter you'd see the voltage change between 0 and ~12 volts. If you connected an oscilloscope, you'd see it's pulse width modulated, i.e. a pulse train of a few hundred hertz where the pulses get wider (longer "on" time) as the ECM output ramps up.

    Or, to put it in other terms, our cars have engine controls that were quite advanced when new. Not too different from what's in a 2019 model; worlds apart from any '70s car.
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    absolutely modulated ,wish I knew the frequency....am I wrong in assuming, that said ,a couple watt tailight bulb should vary in brightness( as the filiment would have residual "heat") as turbo is activated proportionate with ECM supply/requirements?
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    F.G. and as a sidebar to this, the same applies for the CCT's operation correct?

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    A small light bulb would certainly vary in brightness. I would use something very small--an LED and series resistor would be ideal--to avoid overloading the ECM output. It probably has plenty of capacity, but too large a load might cause a "short to B+" fault. An LED has the additional advantage of being linear; an incandescent lamp has a very low resistance when cold.

    And yes, the CCT definitely operates in the same fashion.

    The frequency is probably a few hundred Hertz. If you have a meter with frequency function (e.g. Fluke 87) you could just measure the frequency.

  16. #14
    Motel Room Moderator VAGguy's Avatar
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    Quote Originally Posted by PassatGLS-00 View Post
    Very Good explanation ylwagon, but yourself failed to realize that what kicks in the turbo is as you said: "The so-called-kick-in occurs when the intake manifold pressure becomes....."

    Which gives me the answer and to go and see where and how can I tap into that pressure to know when the manifold gives up its signal.
    Thank you.

    Now I need to figure out how to convert that into a LED that tells me the TURBO starts.

    By the way, in researching that I found something called the "one minute" rule T to ensure a healthy and long trouble free for the Turbo Unit.
    It can be found in a website, but if moderators think is appropriate I can copy it on a posting.
    Your insistence on having a "tell-tale" on when the turbo is working (aka building boost) makes me think you want it to be like the old Buick Grand National (don't know what year exactly). When boost would build, a light would illuminate in the cluster "turbo". It was a gimmick. It just illuminated when it hit a certain PSI manifold pressure.

    A boost gauge is much more informative as it shows not only when the turbo is making boost (raising manifold air pressure), but how much at what RPM and throttle position. It also shows how good your vacuum is and can sometimes tip off of a boost or vac leak.
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    ^ ^ ^ All true there.

    But, I had a random thought today: If OP truly wants a simple "Hey, it's on boost" idiot light (like the GN had), that wouldn't be hard to do - connect a Hobbs switch (of whatever pressure rating OP deems appropriate) to a manifold vacuum source, and wire a light to it. Of course, it's only *slightly* easier than installing an actual boost gauge (depending on where you decide to put the light.) And, it's more of a Build-a-Bear solution than just buying a boost gauge + mount.

  18. #16
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    Quote Originally Posted by cuppie View Post
    connect a Hobbs switch (of whatever pressure rating OP deems appropriate) to a manifold vacuum source, and wire a light to it.
    My turboed Datsun 510 had a water injection arrangement (anti-detonant injection - ADI)that I rigged up, which included a Hobbs switch, indicator light, and rheostat to adjust the injection pump voltage. I found that the Hobbs switch, which I mounted directly to a tapped hole in the manifold, would burn it's contacts due to the engine vibration. After mounting to the firewall instead, connected by a hose, the contacts were OK.

    But... I had a manifold pressure gauge straight in from of me, between the tach and speedo.

  19. #17
    Motel Room Moderator VAGguy's Avatar
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    Now that I have re-read the OP, we are looking for what signal or combination of signals triggers the ECU to activate the various turbo control valves/solenoids to allow boost to build.

    I'm looking at it this way. The ECU has a set map that under X load, X throttle position, X O2 reading, X AIT temp, X MAF reading, MAP reading, etc that it would call for X amount of boost to produce the programmed power delivery and stoichiometric efficiency. In short, it is a constantly variable set of signals by all the sensors that determine how much boost to create and when.

    Anyone, please feel free to correct me or add to the above.
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  20. #18
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    Not disagreeing with any of that, but the OP (if still watching the thread) was evidently not familiar with how a turbo system works. He thought that there is an ECU signal that 'turns on' the turbocharger, which he could use to make an LED light up: there isn't.
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  21. #19
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    Quote Originally Posted by ylwagon View Post
    Not disagreeing with any of that, but the OP (if still watching the thread) was evidently not familiar with how a turbo system works. He thought that there is an ECU signal that 'turns on' the turbocharger, which he could use to make an LED light up: there isn't.
    Yeah. I was trying to give them a little bit of room for interpretation.
    Unless the OP is not logged in and lurking, they haven't seen the majority of our replies. They haven't been on since 5/17
    ylwagon likes this.
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