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Old 05-02-2002, 10:42 PM   #1
corbeil
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Default 200 rpm spike on fast shifts

After trading in my 2.5 rs for a new 02 wrx (turbo timer,redline oil in the tranny), I have noticed a 200 rpm spike when the clutch pedal is depressed .Do all wrx's do this ? Is the ecu doing this ? It never happened with the rs.
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Old 05-02-2002, 10:54 PM   #2
WAlude
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Mine does it... is this because the BOV goes back into the intake track?
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Old 05-02-2002, 10:58 PM   #3
corbeil
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Possibly...I know it only happens on fast shifts.
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Old 05-02-2002, 11:25 PM   #4
StevieD
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Mine does it in 3rd all the time
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Old 05-02-2002, 11:32 PM   #5
BamBooI
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I think its because the turbo is still spooling a little bit. I get it too. I think if you do a search its been covered before though.
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Old 05-02-2002, 11:42 PM   #6
eric m.
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mine does it too. i think it's normal.
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Old 05-03-2002, 12:58 AM   #7
treybomb
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mine too....

possibly because the stock BOV isn't sensitive enough (i.e. doesn't have a low enough threshold) to release WOT boost pressure when the throttle is released for the shift?

it seems, however, that the "rpm spike" on fash shifts has diminished as I put more miles on the car... during the break-in period it annoyed the hell outta me, but now I don't even notice it. Either I've learned to control the engine a little better through the clutch, or for some reason now that it's more "worn in" it doesn't spike as much

- T
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Old 05-03-2002, 02:13 AM   #8
Weedy
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I'm not sure, although I have heard that it it because the stock flywheel is so heavy. It has so much rotating mass that after you disengage the clutch, it takes a little time for it to slow down. I don't really see how this is possible, although that is what I remember being discussed.
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Old 05-03-2002, 09:23 AM   #9
bvl
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This behavior seems to be ECU intervention to me.

Probably a bit of a blip from the ECU in an effort to slow the shift down.

Its not the FW....as the FW is interertial, so it would not spike the RPM as you see, rather it would simply stay where it is, or fall in time delta depending on the amount of inertia it has going for it (which is related to weight...)

BOV could only effect the RPM of the turbine: its not adding fuel/spark or playing with a throttle cable. Don't see how its going to boink RPM 2-300 RPM
when you lilft hard off the throttle

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Old 05-03-2002, 10:11 AM   #10
WRX-Hellfire
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I thought it was designed that way by subaru to help with emissions. The extra rpms were to help burn off the excess fuel since it runs so rich stock.
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Old 05-03-2002, 12:40 PM   #11
blackrex
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Hellfire's right it is for emissions.
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Old 05-03-2002, 12:57 PM   #12
mtb_dude
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I though it was because the BOV vents to the intake and therefore even after you let up on the throttle, the intake is still partially pressurized for a moment. Does anyone with a atmoshphere vent BOV see this spike?
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Old 05-03-2002, 01:49 PM   #13
angus
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the ecu definitely controls this. emissions. my rpm's stick SO late after i let off it's aggravating. i thought someone somewhere was working on a fix for this?
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Old 05-03-2002, 03:16 PM   #14
TerenceT
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Quote:
Originally posted by Angus
the ecu definitely controls this. emissions. my rpm's stick SO late after i let off it's aggravating. i thought someone somewhere was working on a fix for this?
same feeling
sometimes actualy dangerous if you are trying to let the engine brake

Yes, it's for emissions per Heilfire's explanation
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