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Old 01-02-2013, 12:32 AM   #1
Scooby Specialist
Member#: 311781
Join Date: Feb 2012
Location: Canada
2003 WRX w STI V8

Default Could a 10-15% leakdown and low compression cause a slight hesitation?

Hey Guys,

So my motor needs a new set of rings and a hone. Hopefully I can get away with that. Currently they are 99.75, worst case I go to 100mm if need be.

I do have a question, I've always had a slight hesitation on my built shortblock and was wondering if it was because of the high leak down and compression being low.

Cylinder 1 = 117
Cylinder 2 = 117
Cylinder 3 = 105
Cylinder 4 = 105

Cylinder 1: 5%
Cylinder 3: 12%
Haven't done the remaining cylinders but I assume the worst.

CP 8:2:1 Forged Pistons
Manley Turbo Tuff I Beam Rods
Nitrated Crank
MAP H11 head Studs
New Gasket/Seal kit
Rebuilt heads
FIC 1100cc injectors

The hesitation is off boost at 2-3k rpm. If I go into slight boost its a dream to drive. A/F are a solid 14.7 while this hesitation occurs. So it always baffled me and I always tried to tune it out. Its a 2004 STI swap, no air leaks (smoke tested), Fuel trim under 2%. So I'm leaning towards the bad motor build.

Also, might as well ask. Cylinder 4 sparkplug has a slight white residue, compared to the other cylinders that are brownish. I haven't checked the leak down on that cylinder. Usually people have issues with cylinder 1 and 3. Could be the injector being lower in cc, I'll get those cleaned out and retested (bought used). It could be the injector for all I know.

Any thoughts would be awesome! If I missed any crucial information, please ask. I'll edit the first post.

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