2009 335xi - 29DC Injector Cutout on MHD Stage 1+ (only at 1/4 tank), Clunking Noise

n54.sneed · 06-03-2026, 12:56 AM

Hey guys, looking for some help diagnosing a couple of issues on my 2009 335xi. Here's the breakdown:

Car Details:
- 2009 BMW 335xi (N54, AWD/xDrive)
- ~120k miles
- FBO (full bolt-on)
- MHD Stage 1+ (stock map flash)

Timeline of Issues:

Old Problem #1 - Deceleration Clunk: Whenever I'd decelerate and come to a near stop, the car would make a clunking noise. In 2nd gear around 2500 RPM it would make a heavy clunk that would decrease in loudness/feeling in my foot but speed up as RPM went up.

Old Problem #2 - 2nd Gear Clunk Under Load: Same clunk in 2nd gear at ~2500 RPM that was more pronounced under load.

Recent Work Done:
- Replaced all 6 injectors with new Index 11 injectors (~1500 miles ago) - this seemed to fix both clunking issues and they became barely noticeable
- Replaced spark plugs (same time as injectors)
- Replaced fuel pressure regulator with an Amazon one (~500 miles ago, about a month back)

Current Problems:

1. Injector cutout on MHD - Whenever I get into heavy RPMs / throttle / boost, I get injector cutout. The weird thing is it only seems to happen at 1/4 tank or lower. Full tank and it runs fine.

2. Deceleration clunk has returned - The clunking noise when coming to a near stop is back, even though the injectors are new.

What I'm Thinking:
- The 1/4 tank injector cutout has me thinking LPFP or the cheap Amazon fuel pressure regulator could be struggling to feed the HPFP when fuel is low
- Not sure if the clunking is related to fuel issues or a separate drivetrain thing (guibo, driveshaft, diff mounts?)

Questions for the group:
1. Should I be data logging LPFP pressure and rail pressure to confirm HPFP vs LPFP issue?
2. Has anyone experienced injector cutout specifically at low fuel levels? Could the fuel sender / FPR be restricting flow?
3. For the clunking on decel / coming to a stop - should I be looking at the guibo, driveshaft center bearing, or rear diff bushings first on an xDrive?
4. Could the cheap Amazon FPR be causing both issues?

Any logs you'd want to see I can pull from MHD. Appreciate the help, guys.

06-03-2026, 12:56 AM	#1
n54.sneed Registered 0 Rep 1 Posts Drives: 2009 335i x-drive Join Date: Dec 2025 Location: Indianapolis iTrader: (0)	2009 335xi - 29DC Injector Cutout on MHD Stage 1+ (only at 1/4 tank), Clunking Noise Hey guys, looking for some help diagnosing a couple of issues on my 2009 335xi. Here's the breakdown: Car Details: - 2009 BMW 335xi (N54, AWD/xDrive) - ~120k miles - FBO (full bolt-on) - MHD Stage 1+ (stock map flash) Timeline of Issues: Old Problem #1 - Deceleration Clunk: Whenever I'd decelerate and come to a near stop, the car would make a clunking noise. In 2nd gear around 2500 RPM it would make a heavy clunk that would decrease in loudness/feeling in my foot but speed up as RPM went up. Old Problem #2 - 2nd Gear Clunk Under Load: Same clunk in 2nd gear at ~2500 RPM that was more pronounced under load. Recent Work Done: - Replaced all 6 injectors with new Index 11 injectors (~1500 miles ago) - this seemed to fix both clunking issues and they became barely noticeable - Replaced spark plugs (same time as injectors) - Replaced fuel pressure regulator with an Amazon one (~500 miles ago, about a month back) Current Problems: 1. Injector cutout on MHD - Whenever I get into heavy RPMs / throttle / boost, I get injector cutout. The weird thing is it only seems to happen at 1/4 tank or lower. Full tank and it runs fine. 2. Deceleration clunk has returned - The clunking noise when coming to a near stop is back, even though the injectors are new. What I'm Thinking: - The 1/4 tank injector cutout has me thinking LPFP or the cheap Amazon fuel pressure regulator could be struggling to feed the HPFP when fuel is low - Not sure if the clunking is related to fuel issues or a separate drivetrain thing (guibo, driveshaft, diff mounts?) Questions for the group: 1. Should I be data logging LPFP pressure and rail pressure to confirm HPFP vs LPFP issue? 2. Has anyone experienced injector cutout specifically at low fuel levels? Could the fuel sender / FPR be restricting flow? 3. For the clunking on decel / coming to a stop - should I be looking at the guibo, driveshaft center bearing, or rear diff bushings first on an xDrive? 4. Could the cheap Amazon FPR be causing both issues? Any logs you'd want to see I can pull from MHD. Appreciate the help, guys.
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