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This is a discussion on Drive by wire? within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Oh boy... I'm not sure how to comment on the above post. The ECU doesn't "learn octane" before you're out ...

  1. #46
    UnBanned Sinister's Avatar
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    Oh boy... I'm not sure how to comment on the above post.


    The ECU doesn't "learn octane" before you're out of the driveway. It's got a IAM which slowly increases timing based on load until it reaches a knock, and then retards.

    The ECU doesn't "learn" during full boost.. at that point you are in an open loop map, and the ECU is running specifically off a MAP and major sensors.. it doesn't actually learn anything at that point. So if your car is specifically revving up to burn off excess fuel, then it's programmed into the map to do so... But because this is not a Drive By Wire car, then this is not possible..

    On a Drive By Wire car... there is a throttle position sensor that determines how far down your pressing the accelerator pedal... this determines how far to open the actual throttle. This can be intervened by the computer, because the computer controls the whole process. But on a Drive By Cable (or Drive By Throttle as it's also known) (02-05 WRX) the throttle position is DIRECTLY related to the cable being moved by the accelerator pedal.


    So, unfortunately, even though your thinking sounds legitimate.. it's not

    I still maintain my reasoning as described before.
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  3. #47
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    Quote Originally Posted by 1x2 View Post
    I started shifting under load and the ECU relearned to burn the extra fuel (=overrev condition) it didn't matter what rpms I shifted at.
    I want to specifically point this post out....


    And then I want to re-post my initial post into this conversation...

    Quote Originally Posted by Sinister
    It's not that you're letting off the gas and it's rising... your letting off the gas at the same time as the clutch is being disengaged.. the turbo is still spooling, the engine still has momentum, and you just disengaged all load from the engine. Of course the engine is going to rev up a couple hundred rpms.

    And then i want to ask you if you see what I'm saying about why you're "over-revving" while under load, but not very much while you are not under load
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  4. #48
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    Oh boy... I'm not sure how to comment on the above post.
    That seems a little over the top. Nonetheless...

    My bad for tossing in the exaggeration "before I leave the driveway". It could have been worse- I was thinking in terms of even more exaggerated imagery . I was merely trying to head off the obvious warnings about resetting the ECU which seems to drive other threads off track.

    Originally Posted by Sinister
    It's not that you're letting off the gas and it's rising... your letting off the gas at the same time as the clutch is being disengaged.. the turbo is still spooling, the engine still has momentum, and you just disengaged all load from the engine. Of course the engine is going to rev up a couple hundred rpms.
    I like this; please explain the engine's logic to fire the spark plugs so that the rpms rise, especially under this circumstance. Also, can you help with an explanation as to how the plugs fire when the car's decelerating, like before a downshift, and also when using the engine to hold the car back/retard vehicle speed when rolling down hill. How do they know when to fire?

    I have another turbocharged car with an ECU (which is irrelevant to this particular argument) and it drives like a normally aspirated car in terms of the revs dropping during a normal upshift, in or out of boost. FWIW, other posters in other threads also deny same in other of their turbocharged cars- there's another recent thread around here about that.

    Even more specifically, my rex has had the revs spike 500rpm when under heavy load during a 2-3 gear upshift and I'm NOT in boost.

    I appreciate your having stayed with the thread.

    The ECU doesn't "learn" during full boost.. at that point you are in an open loop map, and the ECU is running specifically off a MAP and major sensors...it doesn't actually learn anything at that point.
    No argument; I didn't say it was "learning" at that point.

    So if your car is specifically revving up to burn off excess fuel, then it's programmed into the map to do so... But because this is not a Drive By Wire car, then this is not possible..
    Why would the car have to be drive-by-wire to accomplish this? Isn't that what computers are for? It does make sense to me that if you believe your above statement, that it's impossible if not drive-by-wire, then it also makes sense that you'd blame poor shifting technique, that the OP and I (at least) are holding down the gas pedal too long, since when I take my foot off the pedal, the throttle plate shuts the air off. So going back to the questions I just asked, how do the revs rise with the throttle plate closed?

    The biggest pita about this is that you can't see this happening, but that's internet life...

    Thanks,
    1x2
    Last edited by 1x2; 06-08-2009 at 02:44 PM.

  5. #49
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    Quote Originally Posted by 1x2 View Post
    I like this; please explain the engine's logic to fire the spark plugs so that the rpms rise, especially under this circumstance. Also, can you help with an explanation as to how the plugs fire when the car's decelerating, like before a downshift, and also when using the engine to hold the car back/retard vehicle speed when rolling down hill. How do they know when to fire?
    Plugs fire per stroke. Whether the engine is accelerating, idling, decelerating, etc... there are ALWAYS spark plugs firing. Every single time a piston compresses air and gasoline in the combustion chamber, there needs to be a spark.



    Quote Originally Posted by 1x2 View Post
    Even more specifically, my rex has had the revs spike 500rpm when under heavy load during a 2-3 gear upshift and I'm NOT in boost.

    This comes back to my explanation that when you push on a wall, and then the wall falls through... your hand follows. If an engine has quite a bit of load on it.. then you release it.. it will rev up because it cannot compensate for one instant having resistance against the load, and then the next instant it loses that load.

    Doesn't matter if it's a turbocharged 4 cylinder, or a naturally aspirated v10... load produces boost, and that's why it seems that in high RPMs and high boost it happens more.. There is always load when you are accelerating, driving up hill at a constant rate of speed, or engine braking while going down hill.

    There's a thought... engine brake going down hill, then pop in the clutch... the engine should spike RPMs if my logic is correct... right? I have noticed this happen before on my old F150 inline 6 while engine braking.



    Quote Originally Posted by 1x2 View Post
    Why would the car have to be drive-by-wire to accomplish this? Isn't that what computers are for?
    The computer controls the throttle in a Drive By Wire.. and in a Drive By Cable, the computer does not control the throttle.. instead it reacts to it. Thus the disadvantage.


    Quote Originally Posted by 1x2 View Post
    how do the revs rise with the throttle plate closed?
    First off I'd like you to understand that when a throttle plate is closed.. it's never actually closed. If the throttle plate actually closed, then it would be IMPOSSIBLE to idle. When the throttle plate is at 0%, it is still partially open.

    Secondly... it doesn't have to do with the throttle plate.. it has to do with the engine having inertia, load, resistance, etc.. and then in the blink of an eye losing all of that load and resistance, and so that potential energy is turned into kinetic energy and the engine moves faster for a couple of milliseconds, then it recovers, spools down, all while you engage the next gear, and it gets it's load back.

    It's just like if you engage the clutch by dropping it... it'll bog the engine. Because you're mating two things that are moving at very different speeds... Then you disengage the clutch at a very rapid speed, and the engine doesn't have anything that is causing resistance. Does this sort of make sense?


    Quote Originally Posted by 1x2 View Post
    The biggest pita about this is that you can't see this happening, but that's internet life...
    It happens to me as well... so I researched it when I had first gotten the vehicle to make sure I was fine... 40k miles later, it still does it. It actually got slightly worse because I have a lightweight flywheel which reduces the rotational inertia of the crank shaft, and so the engine doesn't have as much inertia as stock to keep it from accelerating without load.



    Quote Originally Posted by Sinister
    Oh boy... I'm not sure how to comment on the above post.
    Quote Originally Posted by 1x2 View Post
    That seems a little over the top.
    (when I said I'm not sure how to comment... I was serious... I didn't want to REALLY get into it.. but I guess we already did! I wasn't being a smart ass)


    If I was confusing, or didn't answer one of the questions in the manner that you agree with.. please refute or rephrase!

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  6. #50
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    This comes back to my explanation that when you push on a wall, and then the wall falls through... your hand follows. If an engine has quite a bit of load on it.. then you release it.. it will rev up because it cannot compensate for one instant having resistance against the load, and then the next instant it loses that load.
    Then why is the rex the first car I've owned that exhibits this "behavior"?
    Secondly, why did resetting the ECU fix it, not once, but twice, (happily) on the same day, under similar circumstances?

    On the spark plugs firing subject, I was hoping you'd have something to write about timing advance under (what I'd like to call, for brevity's sake) your "load release" theory, that allows the revs to go up, instead of just bogging the engine, since the throttle plate is closed.

    Yes, I understand that the plate's not totally closed, but to a lesser extent than you, I didn't want to have to bring up the idle air stuff, also. I understand that short of reprinting technical manuals here, we need to allow for some shorthand. I'm with you.

    I'm just getting a ton of work done, today, are you?

    1x2

  7. #51
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    Sinister,

    To (try to be) clear:

    One could argue that if, while driving the WRX, I keep the revs up and the (relative) load down, I wouldn't see a rev spike anyway, under any circumstances. But that's not what's been happening over the last 5+ years, and not what happened this weekend.

    After the first reset, and after the ECU relearned (which I promoted, on purpose), it did not matter what the load was on the motor, it always spiked, at least a little.

    But after the second reset, and driving with an eye on the boost gauge, I never experienced a rev spike. I attribute this to my driving style, which kept the engine out of the condition from which the ECU would have to take "learning action".

    There's just nothing else to attribute the difference to (assuming proper testing replication).

    I don't think this is at odds with your "load release" theory; only that there's more than one way to produce a rev spike- and my test points to the ECU being involved, for my shifting style.

    1x2

    P.S. Lots of posters on other threads, knowingly or unknowingly, have opined that it's an "emissions thing". I've thought for some time that I was just viewing the problem from the "wrong" perspective; that if I changed my driving style and/or my shifting timing, that I'd get the same result. I tried, but the rev spike did not go away until the test, this weekend.

    P.P.S. This is my 9th standard-shift car over x years. If it was the only turbo'd std-shift car I owned at present, I could be accused of bad memory, but it is not.
    Last edited by 1x2; 06-08-2009 at 03:57 PM.

  8. #52
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    Quote Originally Posted by 1x2 View Post
    That seems a little over the top. Nonetheless...


    Originally Posted by Sinister
    I like this; please explain the engine's logic to fire the spark plugs so that the rpms rise, especially under this circumstance. Also, can you help with an explanation as to how the plugs fire when the car's decelerating, like before a downshift, and also when using the engine to hold the car back/retard vehicle speed when rolling down hill. How do they know when to fire?
    They don't fire.Also the injectors don't fire as well.Compression alone is used to engine brake.
    Quote Originally Posted by 1x2
    I have another turbocharged car with an ECU (which is irrelevant to this particular argument) and it drives like a normally aspirated car in terms of the revs dropping during a normal upshift, in or out of boost. FWIW, other posters in other threads also deny same in other of their turbocharged cars- there's another recent thread around here about that.
    Comparing two different cars is a moot point.Especially when you don't even know what year/make/model the other car is.Do you think comparing an 86 Buick GNX or a 89 Supra turbo to a 2005 WRX is the same?

    Even more specifically, my rex has had the revs spike 500rpm when under heavy load during a 2-3 gear upshift and I'm NOT in boost.
    Makes no sense.If your under "heavy load" then your boosting.Maybe your just using the wrong termanology.........


    Quote Originally Posted by 1x2
    Why would the car have to be drive-by-wire to accomplish this? Isn't that what computers are for? It does make sense to me that if you believe your above statement, that it's impossible if not drive-by-wire, then it also makes sense that you'd blame poor shifting technique, that the OP and I (at least) are holding down the gas pedal too long, since when I take my foot off the pedal, the throttle plate shuts the air off. So going back to the questions I just asked, how do the revs rise with the throttle plate closed?
    It doesn't have to be drive-by-wire for this to happen.If you have a drive by cable car than the ECU controls air via the IAC valve.If you have a drive by wire then the throttle plate is always cracked and controled by the ECU.They have no IAC valve.If the turbo is still spinning and producing boost all that pressurized air is not always relieved at once.Some of it will be routed either through the IAC valve or past the slightly opened throttle body.What make and model do you even have?
    Last edited by Donkey; 06-08-2009 at 03:56 PM.
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  9. #53
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    They don't fire.
    OK. These ECU-controlled engines are smarter than Sinister's distributor-equipped engines of old, that fired plugs simply because the points gap increased, didn't matter what else was happening, when the cam lobe pushed the points apart, the coil fired a charge into the distributor cap. How does the ECU-equipped engine know when I want to idle, if the plugs don't fire when I'm using the engine to brake downhill? So by extension, when I take my foot off the gas, do the plugs stop firing? When the car's sitting at a stoplight with my foot off the gas, do the plugs stop firing? In sum, how does the engine know when NOT to fire the plugs?

    From there, you could please explain how the revs increase (back to the OPs original question, 'what causes the rev spike') when I take my foot off the gas after I've been accelerating. By this, I mean, how do revs increase unless the timing is being increased? With my foot off the gas, what's the signal to increase the revs? Is it that every time the engine sees "too much" gas in the cylinders, that it increases the timing? Is the question not clear? What is the signal the ECU uses to increase the timing, since this is the only way that revs will increase (you can throw in cold starts in the winter)? Is my question clear, yet? Maybe the ECU doesn't increase the timing- perhaps it comes from somewhere else?

    Also the injectors don't fire as well.
    This part I already believe.
    Comparing two different cars is a moot point.Especially when you don't even know what year/make/model the other car is.
    Not according to Sinister. Did you miss that part of the thread?
    Do you think comparing an 86 Buick GNX or a 89 Supra turbo to a 2005 WRX is the same?
    Depends upon what component or process you're trying to compare.

    Makes no sense.If your under "heavy load" then your boosting.Maybe your just using the wrong termanology
    Is this a physics quiz? If I'm towing a trailer-mounted dragster up a hill on the highway with a n/a auto, the engine in the tow car could be under heavy load. Is it then under boost? Am I terminologically- challenged? Yeah, probably, but not here.

    1x2
    Last edited by 1x2; 06-09-2009 at 12:23 AM.

  10. #54
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    man, it's been a while since i looked at this thread. i completely understand sinister's reasoning with the lifting of the throttle at the same time as pressing the clutch but then again like 1x2 said, i have been driving a stick since i was 15 and have never had this problem. i think that maybe you are both right. i am positive after reading you guy's posts that you know more about how the car works with the ECU and how the sensors play a role than me but maybe if you drive the car in the "sweet spot" after resetting the ECU it will affect the spike. i haven't tried it so i can't say yes or no but 1x2 tried and said it worked so maybe it does to some extent. i am way too tired right meow to read and comprehend half the things you guys are saying so i am gonna hit the hay and re-read this thread in the morning.

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    i have re-read and still don't understand i think 1x2 is getting a smidge ticked off for some reason though. i know it can be frustrating trying to get your point across and/or trying to get a straight answer but Sinister has helped me before and i believe he is a great guy and just trying to help out and the same goes for Donkey. there is no need to get mad at people on a forum. especially when they are trying to help. it's like this thread is turning into youtube video responses or something. anyway, Sooby-Doo if you are still watching this thread that bpv should be delivered today. haven't heard from you but thanks again man.

  12. #56
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    Quote Originally Posted by chattownsubie View Post
    i have re-read and still don't understand i think 1x2 is getting a smidge ticked off for some reason though. i know it can be frustrating trying to get your point across and/or trying to get a straight answer but Sinister has helped me before and i believe he is a great guy and just trying to help out and the same goes for Donkey. there is no need to get mad at people on a forum. especially when they are trying to help. it's like this thread is turning into youtube video responses or something. anyway, Sooby-Doo if you are still watching this thread that bpv should be delivered today. haven't heard from you but thanks again man.
    Yeah sorry man...I'm still here

    Thanks for sending the BPV back...if you ever need anything else just let me know. I've got an ej205 longblock and an ej205 shortblock with just about everything that came on them sitting in my garage so more than likely I'll have an extra part if you need it
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  13. #57
    1x2
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    Sinister has helped me before and i believe he is a great guy and just trying to help out and the same goes for Donkey.
    A fine attitude, to be sure.

    My car now runs like a champ- I was (simply) trying not to be selfish about it, but to share it. I've already put in more than my $.02.

    1x2

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    no prob Shane. i may just take a whole engine next time so be ready...1x2 thanks for all the info. i am glad your car is running better and i have taken yours and Sinisters advice and am shifting when i am in more vaccum and trying to let off the gas a little earlier and my car seems to like it thus far so i am happy.

  15. #59
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    Quote Originally Posted by 1x2 View Post
    OK. These ECU-controlled engines are smarter than Sinister's distributor-equipped engines of old, that fired plugs simply because the points gap increased, didn't matter what else was happening, when the cam lobe pushed the points apart, the coil fired a charge into the distributor cap. How does the ECU-equipped engine know when I want to idle, if the plugs don't fire when I'm using the engine to brake downhill? So by extension, when I take my foot off the gas, do the plugs stop firing? When the car's sitting at a stoplight with my foot off the gas, do the plugs stop firing? In sum, how does the engine know when NOT to fire the plugs?
    Easy.The ECU references speed via the VSS.How fast are you going at a stoplight?The ECU also references TPS..................



    Quote Originally Posted by 1x2
    If I'm towing a trailer-mounted dragster up a hill on the highway with a n/a auto, the engine in the tow car could be under heavy load. Is it then under boost? Am I terminologically- challenged? Yeah, probably, but not here.

    1x2
    We are not talking about a normally aspirated car are we.We are specifically talking about USDM WRX's.
    Last edited by Donkey; 06-10-2009 at 11:55 AM.
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  16. #60
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    Unhappy swapping a 06 sti into a 2002

    Quote Originally Posted by Sooby-Doo View Post
    This is correct. That's why you only see '02-'05 wrx's converted to hybrids, everyone else just gets an ej257 longblock. If we swapped in an ej257 longblock we would have to convert the gas peddle, wiring harness, etc... in order to use DBW. = PITA!!

    DBW vs DBC is essentially "controlled" in the heads, hence the reason for making a hybrid in the first place....believe me, no one "wants" the ej205 heads...lol
    im doing a 06 sti swap on my 02 wrx wagon...im such a noob so bare with me, can someone tell me what else i need to do, to make this swap happen? I have the ecu,engine harness....im getting the gas pedal and wires but what else do i need?!

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