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Boost Pressure Shunt......

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by Rory1980, Nov 6, 2012.

  1. Rory1980

    Rory1980 Active Member

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    Firstly My thanks to all involved on the EGR shunt which really seems to have made a difference on my W210 CDi.
    Carried out the shunt today and initial road tests are promising, before i had boost dropping away or not coming when needed, all thats gone now,
    The next long trip will give it the proper test.

    THE SHUNT - Apologies if this has been discussed before but if it has i have not seen it.

    I can see no reason this would not work on all the Mercedes CDI range indeed anything with variable turbo.

    Like many of you who did the EGR disable Mod i have now a bag of 99x 470 Ohm resistors and a bag of 99 x 1k ohm resistors as is the minimal purchase on Flea bay..

    While i was reving my car today by moving the Throttle position sensor under the bonnet by hand - i noticed the little Variable turbo actuator snapping open and closed as the revs build and drop off ... all the boost pipes swelling up with the force and then dropping off.

    When the engine reaches max boost the ECU tends to back off the boost by de - advancing the turbo vanes so to speak because there is 'no load'
    In an old school turbo system a Wastegate opened via a Diaphram forced against a spring under mechanically set boost levels and the boost was as they say - wasted- no longer spun an Impeller

    Variable turbos do not have this system so basically they drop boost levels by dumping the diaphram pressure resulting in gasses blowing closer to the inside of the turbine where the gases can only push to a certain rpm due to the radius etc. the further outside the center radius the hot gasses are directed the faster it spins and vice verse.

    This variable turbo actuator is controlled by a vacuum which is in turn controlled by an electronic diaphragm controlled by the ECU and its parameters.

    Manufacturers tend to leave a lot of room for error in engine management to cater for worst case scenario environment or servicing.
    It would not surprise me if Mercedes had backed off the boost the engine is capable of supporting to leave it more reliable.
    Of course too much boost is a fault - and too little also a fault.

    With this in mind i thought about what controls this variable turbo diaphram and i came upon the electronic boost sensor.

    The boost sensor is located before the intake manifold and after the intercooler, do not confuse it with the air inlet temp on the opposite side of the pipe which has only 2 wires. ( W210 2001 E220 cdi )


    This sensor is in very close proximity to the radiator fan - after hard driving this may come on at any moment ignition on or off so watch your fingers if any of you attempt this mod !!


    My E220cdi has 380,000 km on it so i don't really mind using it as a guinea pig. It already has a Tuning box fitted to the Fuel rail pressure sensor so is supposed to be 170 /180 hp over the 143 of origin, how true that is i don't know but it certainly snaps through the gears quickly.


    However it does not matter how much fuel you give a car- when the ECU decides boost is enough it cuts it and without air you have only smoke and the engine starts missing one of the three factors needed in combustion triangle of Fuel ,ignition ,air.

    With this boost sensor unplugged the car will refuse to rev past 3000- limp home presumably.

    on the boost sensor connections are three wires, a ground a +5v feed and a return.

    What if we tricked the ECU to thinking the boost was 'not adequate' ' max boost not yet reached' i was thinking, surely it would hold boost not only longer but always be giving slightly more where it used to back it off for safety reasons- Albeit delay the action of the vacuum actuator electronically yet it will still of course back off boost - just at a higher level of psi

    So while the solder iron was hot i snipped into the return reference sensor of the boost sensor and inserted my smallest resistor the 470 k ohms...
    and proceeded take the car for a test drive to see if a fault showed,

    the car stormed along on the main road trip where i have the benefit of a 10km straight it showed not faults up to 160kmh full throttle .

    At the end of this straight i pulled in - let the turbo cool and swapped the 470 ohm for a 1000ohm to see if i could trip a fault.

    Back the road full bore again and still no fault.
    on returning up the damp lanes to the house i floored it with the traction triangle still off and it swung the rear end right out like i have never experienced before except on snow :( !

    I think the engine has more snap - and pulls longer up the rev range in gear before running out of puff. towards 4k revs before i feel the ECU was already starting to retard the diaphram to 'cull' boost levels - not now.

    Yes its maybe half way to a remap, but i would deem it not really that 'crude' because it is a fixed resistor and progressive in that fact all way through the rev range torque load.

    One could probably install a resistor on air mass meter - boost level - throttle position and basically slightly modify every input by a fixed rate and arrive with a very potent and responsive engine still inside its 'throw fault' factory limits and this will be my next trial once the cats are cut out.

    Its just a bit of fun within factory limits and if the power is there why not take it as torque only ads to the driving pleasure.

    When i re opened the bonnet at home i heard crackling from the exhaust system like i have not heard before, as in in like a tuned petrol after a hard run car it had generated a whole lot of heat, maybe more than ever before.
    It is etc work for the turbo no doubt so a cool down period best respected as a decent quality of oil,

    This is where my tests ended as i have chimneys to install today.

    In reality a boost gauge would need to be put into the system and tucked under the wiper while the road test was carried out to see what the benefits are in gained Boost psi at acceleration and on the flat but to cut the story short my car feels more responsive and quicker and i imagine it can only help the MPG in what is already a legend of a car for efficiency.

    Photos of my mod are not really necessary but i can if requested
    Its as simple as a wire with a resistor soldered in it.

    Any inputs etc welcome - if anyone has more time please do a boost gauge test. i also will and report back findings. I don't know where the inlet can be Tee'd into to check pressure but all is possible.


    Happy modding
     
    Last edited: Nov 6, 2012
  2. alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    I have been running quite a high remap on my car for a bout a year now, I am running 22PSI MAX of boost, any more and the stock Merc boost pipes will blow their connections.

    The easier, read better, way would be to map out the limits or move them higher, although this is sometimes not possible with all ECU's

    I estimate I am making around 230 brake and 550nm :p
     
  3. Alex Crow

    Alex Crow Senior Member

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    Other than the increased pressure loads on the intake system, the turbo is the component under greatest stress here, along with exhaust vales to a degree.
    If Dieselman was replying to this thread, he would say watch the EGTs (exhaust gas temps) like a hawk, and don't let them get over ***degC.
    Except he would give a value instead of ***, but IIRC 800 degC max unpstream of vanes.

    So yes, do make sure the oil is always top quality synthetic, and is changed at shortened intervals.

    Beyond all that, I like your thinking, and play similar games myself when I get time (not for months now!).
     
    Last edited: Nov 9, 2012
  4. alexanderfoti

    alexanderfoti MBO Forum Supporter Authorised Forum Supporter

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    Indeed EGTs should be monitored very closesly.

    On my diesel bike I have an EGT probe and even that gets to 450 degress c and its not even turbod!
     
  5. stumo

    stumo Senior Member

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    You should really up the fuel again now, since you have all that extra air to play with. Then you will really see what she can do - er - before something lets go anyway.

    I went the other way on an old Nissan TD27 turbo vehicle I had. First I upped the boost, and that gave a really good power increase, but certain points like idle became a bit rough.

    Then after a while I upped the fuel a bit to match, and that really made a difference.

    In summary, you basically always have excess air in a Diesel, so there is not much benefit in adding even more excess air, unless you add more fuel to go with it.
     
  6. titian

    titian Member

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    update

    Rory, Do you have any further detail on your turbo-boost mod?
    Like actual pressures achieved pre & post mod, 0-100 (kph) times, fuel consumption figures?
    Have you tried any other values for the resistor or have you melted your turbo?
    I have a selection of resistors & sisterflex but I see no point in re-inventing the wheel if you've already done it!
     
  7. oigle

    oigle Senior Member

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    That only applies to older fuel injection setups. Modern common rail automatically increases the fuel as the airflow increases through the MAF - under heavy throttle of course. More boost/more airflow/more fuel.
     
  8. stumo

    stumo Senior Member

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    No not really. Fuel volume in a diesel is like the throttle butterfly in a petrol engine. It can't automatically increase fuel by itself based on air, because that is like stomping on the accelerator pedal. There is no concept of rich/lean in a diesel. Regardless of how fuel is delivered, the principle is the same.

    The ecu has a pre mapped base level of fuel it will deliver at a certain rpm vs pedal position. This is the same principle on both old skool mechanical pumps, and ecu controlled diesels. All other factors are just modifications to that base value.

    Manifold pressure/air doesn't come into it, because its all about fuel volume, air is always mapped (turbo actuation via rpm vs MAP) to be excess to requirements. The only time air comes into it is when MAP is too high, the ecu will back off fuel.

    To up the fuel in this case, you just shove a resistor into the fuel rail pressure sensor circuit, in the same was as was done with MAP.
     
  9. oigle

    oigle Senior Member

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    I partially agree with you but your own statement highlighted above is the issue. MAF is one of those factors that "modify" the base value. Otherwise, why have one? Try driving your ML with the MAF disconnected and see how much power you get. The air volume measured by the MAF is critical in determining the fuel quantity - at heavy/full throttle as I said earlier. The throttle position sensor is very critical in determining the fuel volume too.
    Yes, you can remap for varying amounts of fuel at certain throttle settings/revs but a resistor would increase the flow under all conditions and would just be a fuel waster. My remap upped the fuel to make initial throttle response better but left mid range cruise throttle the same. There is no need to play with the top end for more fuel as the extra flow through the MAF, caused by extra boost, looks after that.
    You are right re saying a diesel can't run lean, but they sure can run too rich - have you not seen diesels spewing black smoke? Excess unburnt fuel.
     
  10. stumo

    stumo Senior Member

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    The MAF is only used for emissions control on these, otherwise theres no point having both MAP and MAF. The CDI2 OM612 in the Oz sprinter doesn't have MAF, only MAP. It also doesn't have EGR, cats and manifold flaps. Unlike our CDI2 ML's. And unlike the US sprinter which has MAF and EGR.

    The fuel modification for MAP is a reduction only. Its there to protect the engine/drivetrain and mostly the turbo, because if the boost is too high vs the target from the separate closed loop turbo control, then something is wrong and torque is then limited.

    There is no reason for the ECU to increase fuel based on higher than normal MAP, because the ECU has been mapped so that at that revs, and that throttle, it injects that amount of fuel and hence always generates that pre-determined level of torque (or less, never more).

    Otherwise if it did inject more, your car would run much more torque when driven in cold climates for just one example, and people driving them in cold countries would be complaining of blown transmissions etc.
     
    Last edited: Nov 11, 2012
  11. oigle

    oigle Senior Member

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    I seem to have lost the plot here somewhere. I didn't know we were talking about Sprinters and their setup. Must have missed something. I was talking about engines such as the 270 or the 220 that the OP first wrote about. Different setups, different controls. Seems we are coming from different directions. No doubt you are right in what you say with Sprinters. Cheers.
     
  12. stumo

    stumo Senior Member

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    They are all OM611 and OM612 and CDI2. I was giving an example of the same MB engine and ECU with both EGR+MAF, and nonEGR+MAP only. What are you saying, now?
     
  13. oigle

    oigle Senior Member

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    My comments in post 9 were purely in relation to motors with MAF control, like the ML motor. When other sensors like MAP are used, the overall control is different as you said. I have no argument there.
    My point was and is that the MAF does have a major effect on the fuelling of any motor with a setup like in the ML, when being used at heavy throttle and that any increase in boost will result in an increase of airflow through the MAF and this will increase the amount of fuel injected. That was my original statement. I did not originally get specific in my choice of engine tech, other than to say "modern common rail diesel". I could have been more precise.
     
  14. stumo

    stumo Senior Member

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    And I'm saying there is no corresponding automatic increase in fuel just because there is more air, on any diesel.

    Fuel is throttle on a diesel, you simply can't have the control system arbitrarily deciding how much torque to produce based on air.

    It is based solely on pedal position vs rpm. The other corrections are there to keep that level of requested torque constant under other changes, or to back off the torque to protect the engine.
     
  15. oigle

    oigle Senior Member

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    Interesting comment.
    So you are saying that an engine at say 1200rpm on full throttle at zero boost will have the same fuel input per revolution as the same motor using full throttle at 3000rpm on 15psi boost? The only difference is the amount of air being "ingested" per revolution. If this were so, there would be no point in turbocharging. The extra air (oxygen) permits more fuel to be burnt, producing more power. There is no other reason for boosting an engine.
     
  16. stumo

    stumo Senior Member

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    No im not saying that at all. Im saying that a diesel engine at full throttle and, say, 1500rpm will have a pre-defined amount of fuel delivered, at that rpm and that throttle. Diesels always run with excess air. This is built into the calculation at the factory. The excess air is mapped separately by the closed loop tubo control. The base fuel map doesn't care how much excess air there is, because its excess, and hss no bearing on how much torque the engine is mapped to produce at that rpm and that throttle.

    There us no way in hell the control system is going to increase the fuel just because there is now more air than normal for whatever reason, because there is supposed to always be more air on a diesel.
     
    Last edited: Nov 11, 2012
  17. oigle

    oigle Senior Member

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    I'm afraid I am just going to have to disagree with you, mate. Sorry. What do you mean by the statement highlited above? A "closed loop turbo control"?
    Lets take another scenario.
    Take a given engine at 3000rpm under full throttle and full boost - it will be given a suitable amount of fuel for the circumstances.
    Take the same engine under the same conditions but (in theory) jam the turbo and prevent it boosting.
    Your theory says that the same amount of fuel is going to be injected. If so, why would it not perform similarly, given your theory of "always having excess air". Of course, without the boost, it will run like any normally aspirated diesel and not perform anywhere near the boosted motor. Why?
    You must understand that a turbo is only an air pump. It is there to provide more oxygen to allow the motor to efficiently burn more fuel and thus create more power. There is only one way for the ecu to know how much fuel it can burn and that is to measure the amount of oxygen it has at its disposal. What device can do this? MAF It is the only device that can do this as a turbo is not directly geared to the motor and boost levels can vary with outside influences - altitude, dirty air cleaner, blocked exhaust etc. There is no set guaranteed amount of oxygen available. A MAP can do a similar job but probably not quite as accurately.
     
  18. stumo

    stumo Senior Member

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    Let me answer it with a question then...

    If you take an NA diesel and slap a turbo on it, or take a OM612 and slap a giant turbo and bigger intercooler on it, will it automatically generate more power?

    The answer is no. It might give a bit more power due to more complete burn of the existing fuelling, but not significantly compared to how much more air is added.

    I think you are getting stuck in a petrol engine paradigm, where the ecu has to allow for the amount of oxygen or the engine will melt.

    I think you're also getting stuck on the excess air thing... it means the engine is mapped at the factory to always run with excess air, whether this be by MAP target, and/or base fuel.
     
    Last edited: Nov 11, 2012
  19. oigle

    oigle Senior Member

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    Strangely enough, the answer is YES. It would make quite a bit more power. There would be a cooler inlet charge which would be denser and the larger turbo would create less back pressure. Both of these things would increase the airflow through the engine and MAF, thus generating more fueling and power, even without more boost.
    Time for bed... maybe we might get some other opinions overnight!! Be interesting to get some other thoughts.
     
  20. stumo

    stumo Senior Member

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    Just to be clear, this is the bit we disagree on in bold.

    The ECU is mapped at the factory to produce a specific maximum torque at every rpm point at 100% pedal. That means a certain maximum fuel volume at each point. That fuel volume requires a specific amount of air to be mapped into the turbo control, to allow excess air for that amount of fuel, also mapped at the factory.

    So by whatever means, you have just added more excess air at that point. More excess air by its very nature is pointless, because it was already excess, ie surplus to requirements. I think this is the key point.

    Its only the fuel volume that determines torque, assuming the engine is operating normally with excess air. Max Torque (hence max fuel) is determined at the factory at every rpm point to protect the drivetrain and engine.

    Take the ml270 for example. It is rated 400Nm max, period. Its not rated 500Nm in iceland, and 300Nm in Darwin. Also, the manual trans ml270 is rated 380Nm - to protect the gearbox, ask yourself how that happens when everything else is the same as the auto trans model. The answer is fuel volume, set at the factory. A fuel volume that has a corresponding MAP target mapped for a level of excess air. No amount of excess-excess air will change that.

    Just a final point to hopefully clarify things... If MAP is lower than target, then fuel volume (and torque) will be lowered to always ensure excess air for the burn. By upping the MAP you will reduce this occurrance, which would give a sense of more power. But the normal maximum fuel (and torque) for that rpm point will never be exceeded by the ecu, otherwise transmissions would be exploding all over the world.

    I hope i have explained it clearer this time.
     
    Last edited: Nov 11, 2012

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