Drive by wire?
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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; i have found that often times when shifting from 2nd and 3rd that my rpms will still rise after i ...

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    Registered User chattownsubie's Avatar
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    Drive by wire?

    i have found that often times when shifting from 2nd and 3rd that my rpms will still rise after i have let off the gas for a second. especially from 3rd. i did a quick search and found that some others have experienced this too and think it may be the drive by wire? is there any way to fix it? could the dealer do anything about it or could i get a tune to help it? it's an 04 wrx cobb stage 2. don't know if the ap maybe adds to the slow reaction of the computer or not. any thoughts and has anyone else had this problem? it wouldn't be surge because the boost drops as soon as i lift but the rpms still climb for a sec. right? also, it happens part throttle and wot.

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    Registered User Sooby-Doo's Avatar
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    Quote Originally Posted by chattownsubie View Post
    i have found that often times when shifting from 2nd and 3rd that my rpms will still rise after i have let off the gas for a second. especially from 3rd. i did a quick search and found that some others have experienced this too and think it may be the drive by wire? is there any way to fix it? could the dealer do anything about it or could i get a tune to help it? it's an 04 wrx cobb stage 2. don't know if the ap maybe adds to the slow reaction of the computer or not. any thoughts and has anyone else had this problem? it wouldn't be surge because the boost drops as soon as i lift but the rpms still climb for a sec. right? also, it happens part throttle and wot.
    Just a thought because this was my issue a few years ago, your BPV or BOV is not functioning properly and therefore not releasing pressure, or at least not enough, at the correct time.

    With me it was that the cone buoy (lack of better term) inside my BOV was marked up and sticking and therefore not rising past the orifice all the way during shifts....same exact symptoms as you. For a while I could simply add a few drops of oil and it'd be fine for a few weeks until eventually I just needed to replace it.

    I personally would not run to redline until you get it straightened out. Over revving at 4500 is one thing, at 7250 it's a whole new ballgame.

    Good luck finding out what the deal is.
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    UnBanned Sinister's Avatar
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    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.

    It's even more noticed when you have an aftermarket flywheel that's lightened, or a lightened pulley.
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    DUB
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    I can't remember where I read this and if it's accurate, but, I think that is normal operation; it does it for emissions reasons.

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    Registered User chattownsubie's Avatar
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    first off sorry about the duplicate thread. i didn't think it went through the first time cause the server was busy. Sinister, i generally don't push in the clutch until after the tranny is disengaged, meaning i lift off the gas and simply pull the shifter out of gear then press the clutch and go into the next. it is a habit of mine which i have heard is good and bad. i put 50,000 miles on my cobra like this and have driven all my other cars with no problems but i may need some advice on this since i am new to the subaru deal. DUB, if that is true it is getting somewhat annoying. i will check out the BPV like Scooby-Doo suggested and i hope that is it because if it is i can make it go away. thanks for all the help and i will post what i find out tomorrow after inspecting the BPV.

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    Registered User Icysheet's Avatar
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    I was under the impression that only STi's have drive-by-wire. Maybe the 08's or 09's have it, but I'm pretty sure 02-07 have a regular throttle connection.

    The rise in RPM is just what sinister said.

    Try letting off the throttle a little early maybe so your engine isn't accelerating as much if it bothers you that the RPM jumps.
    2006 SGM STi Cobb Stage II

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    UnBanned Sinister's Avatar
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    Quote Originally Posted by chattownsubie View Post
    first off sorry about the duplicate thread. i didn't think it went through the first time cause the server was busy. Sinister, i generally don't push in the clutch until after the tranny is disengaged, meaning i lift off the gas and simply pull the shifter out of gear then press the clutch and go into the next. it is a habit of mine which i have heard is good and bad. i put 50,000 miles on my cobra like this and have driven all my other cars with no problems but i may need some advice on this since i am new to the subaru deal. DUB, if that is true it is getting somewhat annoying. i will check out the BPV like Scooby-Doo suggested and i hope that is it because if it is i can make it go away. thanks for all the help and i will post what i find out tomorrow after inspecting the BPV.
    Sometimes I do what you're referring to as well. It saves clutch life because the clutch face isn't receiving any friction. But that doesn't mean that the engine isn't losing load. Everytime you disengage the transmission, you go from a loaded engine to an unloaded engine. Whether or not you're accelerating or decelerating. It's like pushing a wall as hard as you can, then all of a sudden the wall gives way. Your hand will follow through the wall. It's the same with an engine. The engine size, engine balance, drivetrain, vehicle weight, and flywheel inertia all have to do with how prevalent this effect is... but it happens on ALL engines.

    Quote Originally Posted by Icysheet View Post
    I was under the impression that only STi's have drive-by-wire. Maybe the 08's or 09's have it, but I'm pretty sure 02-07 have a regular throttle connection.

    The rise in RPM is just what sinister said.

    Try letting off the throttle a little early maybe so your engine isn't accelerating as much if it bothers you that the RPM jumps.
    All turbocharged 2.5L subaru engines are drive by wire with a 32bit ECU from 2004+.
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    Registered User Icysheet's Avatar
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    Quote Originally Posted by Sinister View Post
    All turbocharged 2.5L subaru engines are drive by wire with a 32bit ECU from 2004+.
    Wasn't the first 2.5 liter wrx made in 2006? Isn't his a 2004 wrx, meaning it's a 2.0 liter and a manual throttle?
    2006 SGM STi Cobb Stage II

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    UnBanned Sinister's Avatar
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    Quote Originally Posted by Icysheet View Post
    Wasn't the first 2.5 liter wrx made in 2006? Isn't his a 2004 wrx, meaning it's a 2.0 liter and a manual throttle?
    That's correct. 2002-2005 WRXs are an EJ205 which has a "Drive By Cable" style throttle.

    2004+ STIs are "Drive By Wire" on the EJ257

    2006+ WRXs are "Drive By Wire" with a EJ255
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    Registered User Sooby-Doo's Avatar
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    Quote Originally Posted by Sinister View Post

    2002-2005 WRXs are an EJ205 which has a "Drive By Cable" style throttle.

    2004+ STIs are "Drive By Wire" on the EJ257

    2006+ WRXs are "Drive By Wire" with a EJ255
    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
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    Registered User chattownsubie's Avatar
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    yeah, i didn't read the replies and went out to look today and sure enough it is drive by really long winding tucked up and in every little nook wire. so i guess that is ruled out. i have a question about removing the bpv. i know there is a gasket there so when i take it off i am assuming i need a new one? also, once i do remove it, what exactly am i looking for. where is that thing Scooby-Doo was talking about. Sininster, it seems, though, that if there is any pressure on the drivetrain like if the rpm were still rising then the trans wouldn't disengage. but either way you have a point because it does disengage and it does keep climbing in rpm's. i just thought that it wouldn't come out of gear until there was no pressure on the drivetrain to move the car.

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    Registered User Sooby-Doo's Avatar
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    Quote Originally Posted by chattownsubie View Post
    yeah, i didn't read the replies and went out to look today and sure enough it is drive by really long winding tucked up and in every little nook wire. so i guess that is ruled out. i have a question about removing the bpv. i know there is a gasket there so when i take it off i am assuming i need a new one? also, once i do remove it, what exactly am i looking for. where is that thing Scooby-Doo was talking about. Sininster, it seems, though, that if there is any pressure on the drivetrain like if the rpm were still rising then the trans wouldn't disengage. but either way you have a point because it does disengage and it does keep climbing in rpm's. i just thought that it wouldn't come out of gear until there was no pressure on the drivetrain to move the car.
    The gasket is one of those "you should definitely use a new one if you can, but more than likely the old one will be OK." kind of things. I've reused the same one a few times over the course of 20k miles with no issues but the last time I had a new gasket on and 300 miles later got a new BOV and the new gasket leaked after I swapped it out....so it's kind of a crap shoot. They are cheap as heck (<$10) so if you can get to a dealership to get one...do it.

    Also, I have an aftermarket BOV so the buoy I mentioned won't be on a stock BPV. Easiest way to rule out the issue is to find a friend with a Subi, swap the BPV and make some test runs. If the issue still occurs, then the BPV was not your problem. If the problem disappears, well...viola!!

    Good luck...I'm curious to find out the end result so keep us informed.
    S&R Built 2.5/2.0 '03 Hybrid w/ PE1818
    Scott Siegel Tuned 308whp/320wtq
    Vogtland Club Spec Springs on KYB AGX's

    ******* I BOOST, therefore I AM! *******

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    Registered User chattownsubie's Avatar
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    yeah, there are only about 3 wrx's in chattanooga that i know of and i don't know any of the people so that may not happen. any idea how much a new one from the dealer would be? or would i be better w/ an aftermarket one that recirculates? i haven't lookes at em b/c i know it isn't needed for my car but if i could get one that doesn't vta for cheaper than the stock bpv then that would be cool.

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    Registered User Sooby-Doo's Avatar
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    Quote Originally Posted by chattownsubie View Post
    yeah, there are only about 3 wrx's in chattanooga that i know of and i don't know any of the people so that may not happen. any idea how much a new one from the dealer would be? or would i be better w/ an aftermarket one that recirculates? i haven't lookes at em b/c i know it isn't needed for my car but if i could get one that doesn't vta for cheaper than the stock bpv then that would be cool.
    Can I trust you?? hmmmm?

    lol...I have a BPV you are welcome to borrow to see if that's your issue. Use it for a week or so and then if that's the problem, shop around for your own...if that's not the problem, you will have saved $100+ dollars by not unnecessarily purchasing a part you don't need. Just mail it back to me when your done.

    PM me your address and I'll ship it out tomorrow for you.

    I'm going to be in TN for Bonnaroo in 2 weeks and have no problem hunting you down if I don't get it back
    S&R Built 2.5/2.0 '03 Hybrid w/ PE1818
    Scott Siegel Tuned 308whp/320wtq
    Vogtland Club Spec Springs on KYB AGX's

    ******* I BOOST, therefore I AM! *******

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    Registered User chattownsubie's Avatar
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    c'mon man. Bonaroo peeps don't hunt people down...but seriously i would really appreciate it if you would do that for me. i did find out today that it only does it when there is boost. if the gauge is reading vaccum the revs stop as soon as i lift off the gas. but if there is even a few pounds it keeps climbing. anyway, i will pm you my address Scooby-Doo and let you decide if you trust me.

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