Usual Fuel Pump Issue

[fjwickham]

Hello guys, my first ever post here.

Sure your all sick of these posts, but need some advice from the experts on what I suspect is a failing fuel pump, and what the best course of action is in my scenario.
Symptoms: 0088 Error code on scanner, hesitancy under load, limp mode (where turbo seems to be off) but can still drive ok just with no power, inconsistent acceleration, all this resets upon ignition restart.

Story: (49,000miles i30N Performance 2019), was having the usual spirited driving in my car, downshifted into 3rd in N mode, put foot down and was like the car suddenly lost half its HP, pulled into services, checked engine bay, no warning lights, no smells. Restarted Engine, and was good again, long story short this has been happening every time I go into N mode and want to have fun, I've stopped putting my foot down until I get this fixed. Thought at first it could have been a spark plug issue, as I called Hyundai UK, who told me my car was part of the re-call, and had the ECU Update and new pump installed about a year ago, so crazy if this new pump is failing already. Changed the sparkplugs today, and a fresh fuel load, and the issue is still here, leading me to believe alongside the code that it is indeed the infamous pump.

What do you guys think? Is there anything else worth checking first before I buy a new (Not Hyundai) fuel pump for about £350 and fit it myself. Thanks and hope it all made sense.

 

[Bu11eT]

is this only happening under full throttle?
keep in mind our car has two fuel pumps, a high pressure one (replaced during that recall) and a lower-pressure one. could be that the low pressure one is bad. But its easy to diagnose with a good tester. Just check the fuel pressures for low and high under full throttle

 

[fjwickham]

is this only happening under full throttle?
keep in mind our car has two fuel pumps, a high pressure one (replaced during that recall) and a lower-pressure one. could be that the low pressure one is bad. But its easy to diagnose with a good tester. Just check the fuel pressures for low and high under full throttle

Thanks for your reply mate, mostly under high throttle, but I have noticed it can happen, although less frequent under low throttle. Here is a quick update (In a nutshell im 90% sure its the HPFP and have ordered an upgrade)

The Diagnostic Evidence

1. Initial Baseline & Sensor Health Check (Key-ON, Engine-OFF)Result: 560 kPa (5.6 bar)What it proves: A faulty pressure sensor or broken wiring would report an impossibly high static value (e.g., 150+ bar) even with the engine off. Reading 5.6 bar matches the exact baseline pressure supplied by the low-pressure in-tank pump, proving your Fuel Rail Pressure Sensor and wiring harness are fully functional.

2. Load & Rev Test (Engine Running)Result: Cold idle at ~12,500–13,000 kPa (125–130 bar); Light 2,000 RPM revs spiking up to ~20,000 kPa (200 bar).What it proves: In neutral under zero engine load, the fuel rail pressure should never reach 200 bar. The internal mechanical spill control valve inside your HPFP is physically sticking shut/open under demand, forcing maximum pump displacement directly into the rail.

3. Physical & Visual InspectionResult: The fitted pump is the original pre-facelift housing (35320-2GTAH0 design) fitted with the clean, dry 2-pin electrical connector. The foam cover was deteriorating, but the essential rear metal heat shield remains intact.What it proves: There are no external fuel or electrical leaks causing signal distortion. This confirms the issue is purely an internal mechanical valve failure inside the pump housing itself. Why the Conclusion Is 100% CorrectThe ECU Failsafe Mechanics: When the internal valve sticks and pushes rail pressure to ~200 bar, the engine control unit detects a critical over-pressure event. To prevent blowing out fuel line seals or damaging injectors, the ECU immediately triggers P0088 and forces the car into a zero-bar boost "soft limp mode". Elimination of Other Variables:Spark blowout/misfires ruled out (new HKS plugs installed).Sensor/wiring fault ruled out (passed static voltage and dynamic response checks).Software update already applied (Service Campaign 40DC23 completed, yet the physical valve is still failing under heat cycles).