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Old 01-14-2022, 03:00 PM   #1
yiiinjun
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Join Date: Aug 2016
Location: NJ
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2017 WRX

Default 2017 WRX Fuel Pump Duty Cycle 71.8%

2017 WRX currently on Cobb Stage 1 tune, only modification is cat-back exhaust.

I have been having severe hesitation/engine stutter on full thorrtle from 2500-4000 rmp, the car performs better at 5000+ rpm, but still with some degree of power loss. I was getting miss fires but no check enginer light.

Recently replaced all 4 plugs and coils, upstream O2, MAF and MAP sensor. Miss fires are gone but still having problems.

I noticed that my low pressure fuel pump has weird duty cycle. I have read some threads on the forum, it seems that fuel pump duty cycle should be switching between 33%, 66% and 99%. But on my car, my fuel pump is switching between 71.8%, 78.8% and 88.1%.

I suspected that I have a clogged fuel pump filter, and I have replaced the whole pump, but still getting the same duty cycle with the new pump. I first thoght that my injector/fuel lines may be clogged, but I think in that case I should be getting higher than normal injector duty cycle, but instead I think I am getting lower than expected injector ducy cycle, only around 0.3% on idle.

Do you guys think it could be my fuel pump controller or relay that has gone bad over time? The duty cycle seems like the control votage is offset by some degree. Thanks.
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Old 01-14-2022, 11:35 PM   #2
That_Boosted_Life
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Chapter/Region: Tri-State
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the 33,66, and 99 is the old ej. the 71.8%, 78.8% and 88.1% duty cycle you are experiencing is correct for the fa20 in the 15+ wrx.

Same for the injector duty cycle. i think the wrx injectors are only good for around 40-42% injector duty cycle. the direct injector duty cycle is different from port injection which is on older ej engines.

What problems are you still currently having now that the misfires are resolved?
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Old 01-14-2022, 11:35 PM   #3
That_Boosted_Life
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double posted

Last edited by That_Boosted_Life; 01-14-2022 at 11:36 PM. Reason: double post
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Old 01-15-2022, 01:45 AM   #4
tegxsi
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What is your HPFP pressure at WOT? AFR?
It probably best to log and post it
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Old 01-15-2022, 02:03 AM   #5
yiiinjun
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The car would accelerate on moderate throttle input, slowly. But if I go like 40% to WOT around 2500rmp to 4000rmp, the car will just give up accelerating, hesitates and shakes, it feels like the engine is choking, and if I hold the throttle and power through the rmp range, after I reach higher rmp, acceleration would become a more smooth, but with some degree of power loss.

I feel like if I keep doing that the ECU will end up in like some kind of limbo zone, it would run rough even with moderate throttle input, significant hesitation and jerkiness on acceleration.

Quote:
Originally Posted by That_Boosted_Life View Post
the 33,66, and 99 is the old ej. the 71.8%, 78.8% and 88.1% duty cycle you are experiencing is correct for the fa20 in the 15+ wrx.

Same for the injector duty cycle. i think the wrx injectors are only good for around 40-42% injector duty cycle. the direct injector duty cycle is different from port injection which is on older ej engines.

What problems are you still currently having now that the misfires are resolved?
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Old 01-15-2022, 02:06 AM   #6
yiiinjun
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I will post the data logs maybe tomorrow. Thanks guys.
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Old 01-19-2022, 02:26 PM   #7
AMBOTTUNED
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Need to post a log of severe hesitation/engine stutter
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