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Old 08-28-2010, 06:47 PM   #1
Bluefoton
Scooby Specialist
 
Member#: 141373
Join Date: Feb 2007
Chapter/Region: E. Canada
Location: Quebec, QC
Vehicle:
2008 2.5i-hatch -
now with a HID retrofit

Default hesitation at 3000-4000 rpm under WOT on hot days

Thought I'd check if anyone experienced it with NAs - basically a very tangible hestitation upon WOT acceleration at 3-4k rpm.

It occurs once in a blue moon, and seems to appear during intense heatsoak - I was just at an auto-x, and noticed it twice (almost a stumble once) at WOT after a sharp curve. To be anally specific, it only happened when the car was floored after braking (so a quick jump from max vacuum to full open throttle.) IATs at this point were exceeding 50C (125 F). Oil and coolant temp were ~ 200F.

Mods are headers and catback, along with a catch can. No tune. No CELs were triggered. Plugs in good condition. It also occured a few times on a red light-to-freeway accelearion on very hot days.

Opinions?
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Old 08-31-2010, 11:56 AM   #2
snoopyone8
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Member#: 42970
Join Date: Sep 2003
Chapter/Region: NESIC
Location: Connecticut USA
Vehicle:
1998 2.5RS BlkDmdPrl
2000 2.5RS SilverthornMet

Default

1)During auto-x's, if I dont have at least 1/2 tank, my fuel will cut-out going through right-handers. Stupid pick-up placement! Its pretty dramatic though, definitely a complete loss of power.

2)I also had a similar condition, just as you described, right before my knock sensor gave up the ghost. It was a slight hesitation at tip-in.

Hopefully this helps!
-adam
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Old 08-31-2010, 01:16 PM   #3
Bluefoton
Scooby Specialist
 
Member#: 141373
Join Date: Feb 2007
Chapter/Region: E. Canada
Location: Quebec, QC
Vehicle:
2008 2.5i-hatch -
now with a HID retrofit

Default

My tank was half-full. Thanks for the info, I wanted to go near empty next time, didn't know cornering would affect fuel supply.
Knock sensor, eh? Does it trigger a CEL, or what are the symptoms when it's gone?
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Old 08-31-2010, 02:49 PM   #4
snoopyone8
Scooby Newbie
 
Member#: 42970
Join Date: Sep 2003
Chapter/Region: NESIC
Location: Connecticut USA
Vehicle:
1998 2.5RS BlkDmdPrl
2000 2.5RS SilverthornMet

Default

Yeah, fuel pump pick up is on driver's right hand side of the tank...you can make (or buy) an anti-slosh box for it. I think scoobymods or ravensblade might have a DIY writeup on it.

The knock sensor does give a code when it finally gives up, but it seems like just before it goes (1-2 weeks of daily driving) it sends funny signals to the ECU without triggering a light and the engine just feels rough and DOP (possibly too far out of time?)

Good luck!,
-adam
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Old 08-31-2010, 04:17 PM   #5
formula91
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Member#: 102984
Join Date: Dec 2005
Chapter/Region: MWSOC
Location: Northbrook, IL
Vehicle:
2005 2.5RS 4EAT
Platinum Silver

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Quote:
Originally Posted by snoopyone8 View Post
1)During auto-x's, if I dont have at least 1/2 tank, my fuel will cut-out going through right-handers. Stupid pick-up placement! Its pretty dramatic though, definitely a complete loss of power.

2)I also had a similar condition, just as you described, right before my knock sensor gave up the ghost. It was a slight hesitation at tip-in.

Hopefully this helps!
-adam
I'm not sure this problem is as apparent on newer imprezas.
Recently a service bulletin was sent out for most GD imprezas where the fuel reserve one-way check valve would prevent fuel from feeding into the pump on hard right handers.

The service bulletin tells you to go remove this valve.
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