2015 Audi S4 B8.5 (Stage 2+) Misfire/EPC/Low Fuel Pressure Woes – Looking for Help!!!
Hey everyone! I’m hoping to get some guidance on an issue I’ve been chasing with my 2015 Audi S4 B8.5 (DSG) that has 92,000 km on it. I bought the car in Summer 2024, and it’s a Stage 2+ build with a 034Motorsport tune (dual pulley, 034 carbon fiber intake, CTS catless test pipes, AWE Track exhaust, CTS heat exchanger, 034 High Pressure Fuel Pump upgrade, etc.). It’s capable of running E85, but I’ve only ever filled it with Shell premium (~11% ethanol here in Canada).
Important Note on Exhaust Changes
I only really started noticing these issues after doing some substantial exhaust work. The previous owner had catless test pipes, which smelled awful and ran very hot for my liking. So, I took the car to Hot Rod Scott’s, where they installed catalytic converters after my mid-pipes, added mufflers post-cats, and essentially converted me from the AWE Track setup to a more Touring-style AWE exhaust system. Almost immediately after these changes, the misfires and EPC issues began cropping up more frequently.
Symptoms & Timeline
October – First EPC & Misfire Event
Driving aggressively in manual mode on the highway. Did a poorly-timed downshift, went WOT, and suddenly got an EPC light. The car shook/rumbling under load.
Towed it to a Euro specialty shop; they found misfires and suspected coils. Spark plugs (two steps colder) looked fine. Replaced coils on affected cylinders, cleared codes, and all was good (for a while).
Second EPC & Misfire Event
Similar scenario: downshift + aggressive acceleration, EPC light, and misfires.
This time, an Audi-specific shop replaced all six coils with APR coils (stronger spark). Spark plugs still checked out fine. Ran fine afterward.
Battery Replacement
Let the car sit for a while; battery died. Installed a brand-new AGM battery (old one was ~10 years old).
Hoped a fresh battery would resolve any electrical/fueling/ignition issues.
March – Third EPC & Misfire Event
Car occasionally felt rough, no codes. Also had a strange park brake code (16985 [U0417] – Invalid Data Received from Park Brake Module), though it never shows on the dash.
On the highway in automatic mode (I’ve been avoiding manual because I thought my shifting was causing issues!), a moderate throttle input triggered the same EPC/misfire event.
Codes pulled (via 034 Bluetooth module):
6352 [P0303] – Cyl 3 Misfire
6351 [P0302] – Cyl 2 Misfire
6371 [P0300] – Random/Multiple Misfire
6183 [P310B] – Low Fuel Pressure Regulation, Fuel Pressure Outside Specification
7948 [P130A] – Hide Cylinder
16985 [U0417] – Invalid Data Received from Park Brake Module
Low Fuel Pressure Concern & Questions
Every time this issue recurs, I keep seeing the Low Fuel Pressure (P310B / 6183) code along with misfires. The car has the 034 High Pressure Fuel Pump piston upgrade, so I’m starting to wonder if there’s a problem with the low-pressure side (in-tank pump, fuel sensor, regulator, etc.) or perhaps something else in the fueling system that’s failing under load.
Could the exhaust modifications (adding cats, mufflers, changing flow characteristics) be affecting fueling or sensor readings?
Could the spark plugs (two steps colder) be a factor, especially at near sea level (Toronto)?
Is there a possibility the low-pressure pump or its control module is failing?
Has anyone else dealt with repeated misfire/EPC codes specifically tied to P310B or fueling issues on a Stage 2+ 3.0T?
Current Status
Coils: All six replaced with APR versions.
Spark Plugs: Two steps colder, but they appear healthy.
Battery: Replaced with a new AGM.
Exhaust: Cats added after mid-pipes, plus mufflers (converted from AWE Track to Touring style).
Despite all this, the car keeps misfiring under load and throwing EPC lights. Two different Audi-focused shops are stumped. Any advice or previous experience with a similar setup would be massively appreciated!
2015 S4 B8.5 | 92,000 km | 034 Stage 2+ | APR Coils | 2-step colder plugs | 034 HPFP | CTS HX | Catless test pipes (now catted mid-pipes) | AWE Touring Exhaust
If you’ve faced something similar—especially with the P310B “Low Fuel Pressure” code—please let me know what solved it for you. Thanks in advance for your help!
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