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Old 09-12-2020, 03:45 AM   #1
Barles Charkley
Scooby Newbie
 
Member#: 516825
Join Date: Jul 2020
Chapter/Region: TXIC
Vehicle:
2011 Impreza WRX
White

Default "Pffft" + stumble under load

Hey guys,

I used the search function to no avail, or I found nothing specifically with this issue.

Car is 2011 WRX with 105k miles:
  • Invidia catless downpipe
  • Invidia N1 catback
  • Cobb SF intake
  • Accessport Stage 2+ SF OTS tune, low wastegate duty cycle

The car runs flawlessly with the exception of a "Pffft" noise and a stumble immediately after the noise, under a load. I have never been able to replicate the issue at idle. Seems to happen more when the engine is warming up. To give you an idea, I'll be at about 2.5k rpm on the highway and I'll get a sound like someone opening up a twist-off beer bottle coming from somewhere around the driver's side. This is the "Pffft" I was describing. Then immediately after, I get the slightest stumble and loss of power. There is no measurable time gap. The stumble happens at the very end of the "pfft." I feel a small driveline shock all the way through the car. It seems to be independent of engine speed or boost pressure. No check engine light or pending codes.

I am "mechanical" and have done lots of work on many cars, I just don't know where to start on these engines in particular, or if this is a common or known issue in the WRX community. Since the car is 10 years old, I suspect a loose fitting on the charge piping somewhere, but I thought I would consult the collective WRX hive mind first. I almost suspected a bad head gasket at first, but there is no external leak or coolant/oil and no mixing of coolant/oil, and temperature remains solid at slightly less than halfway on the gauge. Any help is greatly appreciated.
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Old 09-14-2020, 01:50 PM   #2
Barles Charkley
Scooby Newbie
 
Member#: 516825
Join Date: Jul 2020
Chapter/Region: TXIC
Vehicle:
2011 Impreza WRX
White

Default

Bueller?
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Old 09-14-2020, 02:40 PM   #3
BlackFighter
Scooby Specialist
 
Member#: 193940
Join Date: Nov 2008
Location: Philly
Vehicle:
2004 WRX STI Black
RalliSpec Shortblock

Default

Sounds like you are describing your A/C engaging. did you have AC running when you heard the sounds?

If not AC then it might be a boost leak.
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